2:55 p.m.
On Tue, Oct 15, 2013 at 02:30:34PM +0800, Gao feng wrote:
Hi Toshiyuki-san,
Toshiuki and Gao,
On 10/15/2013 12:43 PM, Toshiyuki Okajima wrote:
> The backlog cannot be consumed when audit_log_start is running on auditd
> even if audit_log_start calls wait_for_auditd to consume it.
> The situation is a deadlock because only auditd can consume the backlog.
> If the other process needs to send the backlog, it can be also stopped
> by the deadlock.
>
> So, audit_log_start running on auditd should not stop.
>
> You can see the deadlock with the following reproducer:
> # auditctl -a exit,always -S all
> # reboot
Hmm, I see, There may be other code paths that auditd can call
audit_log_start except
audit_log_config_change. so it's better to handle this problem in audit_log_start.
but current task is only meaningful when gfp_mask & __GFP_WAIT is true.
so maybe the below patch is what you want.
I have been following this thread with interest. I like the general
evolution of this patch. The first patch was a bit too abrupt, dropping
too much, but this one makes much more sense. I would be tempted to
make the reserve even bigger.
I see that you should be using a kernel that has included commit
8ac1c8d5 (which made it into v3.12-rc3)
audit: fix endless wait in audit_log_start()
That was an obvious bug, but I was still concerned about the cause of
the initial wait. There are other fixes and ideas in the works that
should alleviate some of the pressure to make the service more usable.
https://lkml.org/lkml/2013/9/18/453
I have tested with and without this v3 patch and I don't see any
significant difference with the reproducer provided above. I'm also
testing with a reproducer of the endless wait bug (readahead-collector).
What are your expected results? What are your actual results in each
case? How are they different?
diff --git a/kernel/audit.c b/kernel/audit.c
index 7b0e23a..10b4545 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1095,7 +1095,9 @@ struct audit_buffer *audit_log_start(struct audit_context
struct audit_buffer *ab = NULL;
struct timespec t;
unsigned int uninitialized_var(serial);
- int reserve;
+ int reserve = 5; /* Allow atomic callers to go up to five
+ entries over the normal backlog limit */
+
unsigned long timeout_start = jiffies;
if (audit_initialized != AUDIT_INITIALIZED)
@@ -1104,11 +1106,12 @@ struct audit_buffer *audit_log_start(struct audit_contex
if (unlikely(audit_filter_type(type)))
return NULL;
- if (gfp_mask & __GFP_WAIT)
- reserve = 0;
- else
- reserve = 5; /* Allow atomic callers to go up to five
- entries over the normal backlog limit */
+ if (gfp_mask & __GFP_WAIT) {
+ if (audit_pid && audit_pid == current->pid)
+ gfp_mask &= ~__GFP_WAIT;
+ else
+ reserve = 0;
+ }
while (audit_backlog_limit
&& skb_queue_len(&audit_skb_queue) > audit_backlog_limit +
reserv
- RGB
--
Richard Guy Briggs <rbriggs(a)redhat.com>
Senior Software Engineer
Kernel Security
AMER ENG Base Operating Systems
Remote, Ottawa, Canada
Voice: +1.647.777.2635
Internal: (81) 32635
Alt: +1.613.693.0684x3545
12:55 a.m.
New subject: [BUG][PATCH] audit: audit_log_start running on auditd should not stop
On 10/24/2013 03:55 AM, Richard Guy Briggs wrote:
On Tue, Oct 15, 2013 at 02:30:34PM +0800, Gao feng wrote:
> Hi Toshiyuki-san,
Toshiuki and Gao,
> On 10/15/2013 12:43 PM, Toshiyuki Okajima wrote:
>> The backlog cannot be consumed when audit_log_start is running on auditd
>> even if audit_log_start calls wait_for_auditd to consume it.
>> The situation is a deadlock because only auditd can consume the backlog.
>> If the other process needs to send the backlog, it can be also stopped
>> by the deadlock.
>>
>> So, audit_log_start running on auditd should not stop.
>>
>> You can see the deadlock with the following reproducer:
>> # auditctl -a exit,always -S all
>> # reboot
> Hmm, I see, There may be other code paths that auditd can call audit_log_start
except
> audit_log_config_change. so it's better to handle this problem in
audit_log_start.
>
> but current task is only meaningful when gfp_mask & __GFP_WAIT is true.
> so maybe the below patch is what you want.
I have been following this thread with interest. I like the general
evolution of this patch. The first patch was a bit too abrupt, dropping
too much, but this one makes much more sense. I would be tempted to
make the reserve even bigger.
I see that you should be using a kernel that has included commit
8ac1c8d5 (which made it into v3.12-rc3)
audit: fix endless wait in audit_log_start()
That was an obvious bug,
include or not include?
The problem is, if the audit_backlog_limit is 3, but there are 5 tasks
calling audit_log_start, so 2 tasks will wait auditd to consume
audit_skb_queue. if before auditd consumes skbs, somebody want to kill
auditd, and auditd will set the audit_pid to zero, this will triger an
audit message. so auditd will wait for himself. and this waiting is endless,
since auditd cann't consume audit_skb_queue any more.
the commit 8ac1c8d5 prevent this problem happening. because if once a task is
blocked over the audit_backlog_wait_time. the audit_backlog_wait_time will
be set to zero(audit_backlog_wait_overflow which is zero). so the other tasks
will not wait anymore. but I'm confused if this is what we expected? these
audit messages will lost once any task is blocked over audit_backlog_wait_time.
So, AFAIK if commit 8ac1c8d5 exist, this patch is not necessary, but
we still do something to fix the problem commit 8ac1c8d5 brings.
but I was still concerned about the cause of
the initial wait. There are other fixes and ideas in the works that
should alleviate some of the pressure to make the service more usable.
https://lkml.org/lkml/2013/9/18/453
I have tested with and without this v3 patch and I don't see any
significant difference with the reproducer provided above. I'm also
testing with a reproducer of the endless wait bug (readahead-collector).
What are your expected results? What are your actual results in each
case? How are they different?
> diff --git a/kernel/audit.c b/kernel/audit.c
> index 7b0e23a..10b4545 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -1095,7 +1095,9 @@ struct audit_buffer *audit_log_start(struct audit_context
> struct audit_buffer *ab = NULL;
> struct timespec t;
> unsigned int uninitialized_var(serial);
> - int reserve;
> + int reserve = 5; /* Allow atomic callers to go up to five
> + entries over the normal backlog limit */
> +
> unsigned long timeout_start = jiffies;
>
> if (audit_initialized != AUDIT_INITIALIZED)
> @@ -1104,11 +1106,12 @@ struct audit_buffer *audit_log_start(struct audit_contex
> if (unlikely(audit_filter_type(type)))
> return NULL;
>
> - if (gfp_mask & __GFP_WAIT)
> - reserve = 0;
> - else
> - reserve = 5; /* Allow atomic callers to go up to five
> - entries over the normal backlog limit */
> + if (gfp_mask & __GFP_WAIT) {
> + if (audit_pid && audit_pid == current->pid)
> + gfp_mask &= ~__GFP_WAIT;
> + else
> + reserve = 0;
> + }
>
> while (audit_backlog_limit
> && skb_queue_len(&audit_skb_queue) >
audit_backlog_limit + reserv
- RGB
--
Richard Guy Briggs <rbriggs(a)redhat.com>
Senior Software Engineer
Kernel Security
AMER ENG Base Operating Systems
Remote, Ottawa, Canada
Voice: +1.647.777.2635
Internal: (81) 32635
Alt: +1.613.693.0684x3545
2:35 p.m.
New subject: [BUG][PATCH] audit: audit_log_start running on auditd should not stop
On Thu, Oct 24, 2013 at 01:55:37PM +0800, Gao feng wrote:
On 10/24/2013 03:55 AM, Richard Guy Briggs wrote:
> On Tue, Oct 15, 2013 at 02:30:34PM +0800, Gao feng wrote:
>> Hi Toshiyuki-san,
>
> Toshiuki and Gao,
>
>> On 10/15/2013 12:43 PM, Toshiyuki Okajima wrote:
>>> The backlog cannot be consumed when audit_log_start is running on auditd
>>> even if audit_log_start calls wait_for_auditd to consume it.
>>> The situation is a deadlock because only auditd can consume the backlog.
>>> If the other process needs to send the backlog, it can be also stopped
>>> by the deadlock.
>>>
>>> So, audit_log_start running on auditd should not stop.
>>>
>>> You can see the deadlock with the following reproducer:
>>> # auditctl -a exit,always -S all
>>> # reboot
>
>> Hmm, I see, There may be other code paths that auditd can call audit_log_start
except
>> audit_log_config_change. so it's better to handle this problem in
audit_log_start.
>>
>> but current task is only meaningful when gfp_mask & __GFP_WAIT is true.
>> so maybe the below patch is what you want.
>
> I have been following this thread with interest. I like the general
> evolution of this patch. The first patch was a bit too abrupt, dropping
> too much, but this one makes much more sense. I would be tempted to
> make the reserve even bigger.
>
> I see that you should be using a kernel that has included commit
> 8ac1c8d5 (which made it into v3.12-rc3)
> audit: fix endless wait in audit_log_start()
> That was an obvious bug,
include or not include?
You say you tested on v3.12-rc4, which does (should?) include this fix.
The problem is, if the audit_backlog_limit is 3, but there are 5
tasks
calling audit_log_start, so 2 tasks will wait auditd to consume
audit_skb_queue. if before auditd consumes skbs, somebody want to kill
auditd, and auditd will set the audit_pid to zero, this will triger an
audit message. so auditd will wait for himself. and this waiting is endless,
since auditd cann't consume audit_skb_queue any more.
the commit 8ac1c8d5 prevent this problem happening. because if once a task is
blocked over the audit_backlog_wait_time. the audit_backlog_wait_time will
be set to zero(audit_backlog_wait_overflow which is zero). so the other tasks
will not wait anymore. but I'm confused if this is what we expected? these
audit messages will lost once any task is blocked over audit_backlog_wait_time.
This is configurable. The default is this behaviour, so that if there
is a problem with the audit subsystem, it will give a reasonable chance
for auditd to catch up, then give up, make noise in the syslog (and
configured colsoles) and then continue. Other auditd configurations
allow the system to halt if this condition occurs.
There is another patch coming that will set that audit_backlog_wait_time
back to the original value once auditd has recovered. It is not
upstream yet.
So, AFAIK if commit 8ac1c8d5 exist, this patch is not necessary, but
we still do something to fix the problem commit 8ac1c8d5 brings.
This is the condition in which I am interested. Do you have a way to
clearly show this condition without your patch and a way to show it is
solved with your patch? I'm looking for a clear reproducer.
but I was still concerned about the cause of
> the initial wait. There are other fixes and ideas in the works that
> should alleviate some of the pressure to make the service more usable.
> https://lkml.org/lkml/2013/9/18/453
>
> I have tested with and without this v3 patch and I don't see any
> significant difference with the reproducer provided above. I'm also
> testing with a reproducer of the endless wait bug (readahead-collector).
>
> What are your expected results? What are your actual results in each
> case? How are they different?
>
>> diff --git a/kernel/audit.c b/kernel/audit.c
>> index 7b0e23a..10b4545 100644
>> --- a/kernel/audit.c
>> +++ b/kernel/audit.c
>> @@ -1095,7 +1095,9 @@ struct audit_buffer *audit_log_start(struct audit_context
>> struct audit_buffer *ab = NULL;
>> struct timespec t;
>> unsigned int uninitialized_var(serial);
>> - int reserve;
>> + int reserve = 5; /* Allow atomic callers to go up to five
>> + entries over the normal backlog limit */
>> +
>> unsigned long timeout_start = jiffies;
>>
>> if (audit_initialized != AUDIT_INITIALIZED)
>> @@ -1104,11 +1106,12 @@ struct audit_buffer *audit_log_start(struct
audit_contex
>> if (unlikely(audit_filter_type(type)))
>> return NULL;
>>
>> - if (gfp_mask & __GFP_WAIT)
>> - reserve = 0;
>> - else
>> - reserve = 5; /* Allow atomic callers to go up to five
>> - entries over the normal backlog limit */
>> + if (gfp_mask & __GFP_WAIT) {
>> + if (audit_pid && audit_pid == current->pid)
>> + gfp_mask &= ~__GFP_WAIT;
>> + else
>> + reserve = 0;
>> + }
>>
>> while (audit_backlog_limit
>> && skb_queue_len(&audit_skb_queue) >
audit_backlog_limit + reserv
>
> - RGB
- RGB
--
Richard Guy Briggs <rbriggs(a)redhat.com>
Senior Software Engineer
Kernel Security
AMER ENG Base Operating Systems
Remote, Ottawa, Canada
Voice: +1.647.777.2635
Internal: (81) 32635
Alt: +1.613.693.0684x3545
8:36 p.m.
New subject: [BUG][PATCH] audit: audit_log_start running on auditd should not stop
Hi.
Thanks for your interest.
(2013/10/24 4:55), Richard Guy Briggs wrote:
On Tue, Oct 15, 2013 at 02:30:34PM +0800, Gao feng wrote:
> Hi Toshiyuki-san,
Toshiuki and Gao,
> On 10/15/2013 12:43 PM, Toshiyuki Okajima wrote:
>> The backlog cannot be consumed when audit_log_start is running on auditd
>> even if audit_log_start calls wait_for_auditd to consume it.
>> The situation is a deadlock because only auditd can consume the backlog.
>> If the other process needs to send the backlog, it can be also stopped
>> by the deadlock.
>>
>> So, audit_log_start running on auditd should not stop.
>>
>> You can see the deadlock with the following reproducer:
>> # auditctl -a exit,always -S all
>> # reboot
> Hmm, I see, There may be other code paths that auditd can call audit_log_start
except
> audit_log_config_change. so it's better to handle this problem in
audit_log_start.
>
> but current task is only meaningful when gfp_mask & __GFP_WAIT is true.
> so maybe the below patch is what you want.
I have been following this thread with interest. I like the general
evolution of this patch. The first patch was a bit too abrupt, dropping
too much, but this one makes much more sense. I would be tempted to
make the reserve even bigger.
I see that you should be using a kernel that has included commit
8ac1c8d5 (which made it into v3.12-rc3)
audit: fix endless wait in audit_log_start()
That was an obvious bug, but I was still concerned about the cause of
the initial wait. There are other fixes and ideas in the works that
should alleviate some of the pressure to make the service more usable.
https://lkml.org/lkml/2013/9/18/453
I have tested with and without this v3 patch and I don't see any
significant difference with the reproducer provided above. I'm also
testing with a reproducer of the endless wait bug (readahead-collector).
What are your expected results? What are your actual results in each
case? How are they different?
OK. I try to describe.
1) I found that the system cannot reboot smoothly because auditd daemon can stop for 60
seconds.
2) As the result of my investigation of this problem, I found that audit_log_start
executed
on auditd called wait_for_auditd and stopped for "audit_backlog_wait_time".
Calling wait_for_auditd is to let auditd consume the backlog during this sleep.
However, when wait_for_auditd is called on auditd, the backlog cannot be consumed during
this time.
In addition, audit_log_start called by other processes can also stop while auditd is
stopping.
So, wait_for_auditd called on auditd is meaningless.
3) Therefore, I made the v3 patch that audit_log_start executed on auditd doesn't call
wait_for_auditd.
4) On my environment, I couldn't see the situation that auditd stopped for 60 seconds
by using
this patch.
5) So, I thought this problem could be fixed.
But after I received your comment, I encountered the other problem that auditd can stop
for
60 seconds when I tried this patch on the other environment installed
"systemd".
So, I think you encountered the other problem that was the same as mine.
The following situation was occurred:
zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
PID: 1 TASK: ffff88007c7d8000 CPU: 0 COMMAND: "systemd"
#0 [ffff88007c7758d8] __schedule at ffffffff815f231a
#1 [ffff88007c775950] schedule at ffffffff815f2a79
#2 [ffff88007c775960] schedule_timeout at ffffffff815f0f93
#3 [ffff88007c775a10] audit_log_start at ffffffff810d7d09
#4 [ffff88007c775ab0] audit_log_common_recv_msg at ffffffff810d8068
#5 [ffff88007c775b00] audit_receive_msg at ffffffff810d8ca0
#6 [ffff88007c775bb0] audit_receive at ffffffff810d8f98
#7 [ffff88007c775be0] netlink_unicast at ffffffff8150bf31
#8 [ffff88007c775c30] netlink_sendmsg at ffffffff8150c2b1
#9 [ffff88007c775cc0] sock_sendmsg at ffffffff814ca3fc
#10 [ffff88007c775e50] sys_sendto at ffffffff814ccd6d
#11 [ffff88007c775f80] system_call_fastpath at ffffffff815fc259
RIP: 00007fbee5653543 RSP: 00007fff23d684b8 RFLAGS: 00000246
RAX: 000000000000002c RBX: ffffffff815fc259 RCX: ffffffffffffffff
RDX: 0000000000000078 RSI: 00007fff23d5d8c0 RDI: 0000000000000003
RBP: 0000000000000003 R8: 00007fff23d5d8b0 R9: 000000000000000c
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000050
R13: 00007fff23d66380 R14: 000000000000046b R15: 0000000000000067
ORIG_RAX: 000000000000002c CS: 0033 SS: 002b
PID: 488 TASK: ffff880036edcbf0 CPU: 1 COMMAND: "auditd"
#0 [ffff88007ba93a98] __schedule at ffffffff815f231a
#1 [ffff88007ba93b10] schedule at ffffffff815f2a79
#2 [ffff88007ba93b20] schedule_preempt_disabled at ffffffff815f2d0e
#3 [ffff88007ba93b30] __mutex_lock_slowpath at ffffffff815f1903
#4 [ffff88007ba93b90] mutex_lock at ffffffff815f143a
#5 [ffff88007ba93bb0] audit_receive at ffffffff810d8f71
#6 [ffff88007ba93be0] netlink_unicast at ffffffff8150bf31
#7 [ffff88007ba93c30] netlink_sendmsg at ffffffff8150c2b1
#8 [ffff88007ba93cc0] sock_sendmsg at ffffffff814ca3fc
#9 [ffff88007ba93e50] sys_sendto at ffffffff814ccd6d
#10 [ffff88007ba93f80] system_call_fastpath at ffffffff815fc259
RIP: 00007fc256ff16f3 RSP: 00007fffff6b39d8 RFLAGS: 00010202
RAX: 000000000000002c RBX: ffffffff815fc259 RCX: 0000000000000000
RDX: 0000000000000030 RSI: 00007fffff6b3a00 RDI: 0000000000000003
RBP: 0000000000000003 R8: 00007fffff6b39f0 R9: 000000000000000c
R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000005
R13: 00007fffff6ba3f0 R14: 00000000000003e9 R15: 0000000000000020
ORIG_RAX: 000000000000002c CS: 0033 SS: 002b
systemd |auditd
-------------------------------------------+-----------------------------------
... |
-> audit_receive |...
-> mutex_lock(&audit_cmd_mutex) |-> audit_receive
... -> audit_log_start | -> mutex_lock(&audit_cmd_mutex)
-> wait_for_auditd | // wait for systemd
-> schedule_timeout(60*HZ) |
zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
V3 patch cannot fix the above problem. V3 patch only fixes the problem that
audit_log_start
on auditd stops for 60 seconds in vain. The other problem is that auditd stops for
about 60 seconds by the mutex lock which the other process gets.
If the other process is "systemd", changing V3 patch like the following fixes
the other problem.
(I confirm that the new v3 patch can fix the other problem which I encountered on
installed
"systemd" environment.)
zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
@@ -1104,11 +1105,12 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx,
gfp_t gfp_mask,
if (unlikely(audit_filter_type(type)))
return NULL;
- if (gfp_mask & __GFP_WAIT)
- reserve = 0;
- else
- reserve = 5; /* Allow atomic callers to go up to five
- entries over the normal backlog limit */
+ if (gfp_mask & __GFP_WAIT) {
+ if (audit_pid && (current->pid == 1 || audit_pid == current->pid))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ gfp_mask &= ~__GFP_WAIT;
+ else
+ reserve = 0;
+ }
zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
However, if the other process is not "systemd", another problem cannot be
corrected by a
simple correction.
At present, a drastic method to fix the other problem doesn't occur to me.
Regards,
Toshiyuki Okajima
> diff --git a/kernel/audit.c b/kernel/audit.c
> index 7b0e23a..10b4545 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -1095,7 +1095,9 @@ struct audit_buffer *audit_log_start(struct audit_context
> struct audit_buffer *ab = NULL;
> struct timespec t;
> unsigned int uninitialized_var(serial);
> - int reserve;
> + int reserve = 5; /* Allow atomic callers to go up to five
> + entries over the normal backlog limit */
> +
> unsigned long timeout_start = jiffies;
>
> if (audit_initialized != AUDIT_INITIALIZED)
> @@ -1104,11 +1106,12 @@ struct audit_buffer *audit_log_start(struct audit_contex
> if (unlikely(audit_filter_type(type)))
> return NULL;
>
> - if (gfp_mask & __GFP_WAIT)
> - reserve = 0;
> - else
> - reserve = 5; /* Allow atomic callers to go up to five
> - entries over the normal backlog limit */
> + if (gfp_mask & __GFP_WAIT) {
> + if (audit_pid && audit_pid == current->pid)
> + gfp_mask &= ~__GFP_WAIT;
> + else
> + reserve = 0;
> + }
>
> while (audit_backlog_limit
> && skb_queue_len(&audit_skb_queue) >
audit_backlog_limit + reserv
- RGB
--
Richard Guy Briggs <rbriggs(a)redhat.com>
Senior Software Engineer
Kernel Security
AMER ENG Base Operating Systems
Remote, Ottawa, Canada
Voice: +1.647.777.2635
Internal: (81) 32635
Alt: +1.613.693.0684x3545
10:12 a.m.
New subject: [BUG][PATCH] audit: audit_log_start running on auditd should not stop
On Fri, 2013-10-25 at 10:36 +0900, Toshiyuki Okajima wrote:
systemd |auditd
-------------------------------------------+-----------------------------------
... |
-> audit_receive |...
-> mutex_lock(&audit_cmd_mutex) |-> audit_receive
... -> audit_log_start | -> mutex_lock(&audit_cmd_mutex)
-> wait_for_auditd | // wait for systemd
-> schedule_timeout(60*HZ) |
Ugggh, definitely a problem. Adding a similar hack to systemd really
does not seem like an acceptable answer. It seems to me that in
audit_receive_msg()
case AUDIT_USER:
case AUDIT_FIRST_USER_MSG ... AUDIT_LAST_USER_MSG:
case AUDIT_FIRST_USER_MSG2 ... AUDIT_LAST_USER_MSG2:
we do not need to hold the audit_cmd_mutex. So a quick and dirty patch
should be to just drop the mutex there (and we need to verify there
aren't issues running the audit_filter_user() without the lock). That
will take care of systemd and anything USING audit. It still means that
you could race with something configuring audit and auditd shutting
down. Seems like a good quick and dirty 'fix' while we work on a better
fix...
To take care of that I think maybe we could drop the cmd_mutex every
time we call audit_log_start. That's not necessarily going to be
pretty. Maybe make a new switch at the top of the function which knows
which operations we are going to have to allocate an audit_buffer. Drop
the lock, allocate the buffer, then retake the lock to finish running
audit_receive_msg()....
Maybe that second option isn't so hard and we can go directly after that
instead of just dealing with userspace audit messages?
Thoughts?
4:20 a.m.
New subject: [BUG][PATCH] audit: audit_log_start running on auditd should not stop
Hi.
(2013/10/26 0:12), Eric Paris wrote:
On Fri, 2013-10-25 at 10:36 +0900, Toshiyuki Okajima wrote:
> systemd |auditd
> -------------------------------------------+-----------------------------------
> ... |
> -> audit_receive |...
> -> mutex_lock(&audit_cmd_mutex) |-> audit_receive
> ... -> audit_log_start | ->
mutex_lock(&audit_cmd_mutex)
> -> wait_for_auditd | // wait for systemd
> -> schedule_timeout(60*HZ) |
Ugggh, definitely a problem. Adding a similar hack to systemd
really
does not seem like an acceptable answer. It seems to me that in
I think so, too.
We should fix it against the various cases.
audit_receive_msg()
case AUDIT_USER:
case AUDIT_FIRST_USER_MSG ... AUDIT_LAST_USER_MSG:
case AUDIT_FIRST_USER_MSG2 ... AUDIT_LAST_USER_MSG2:
we do not need to hold the audit_cmd_mutex. So a quick and dirty patch
should be to just drop the mutex there (and we need to verify there
aren't issues running the audit_filter_user() without the lock). That
will take care of systemd and anything USING audit. It still means that
you could race with something configuring audit and auditd shutting
down. Seems like a good quick and dirty 'fix' while we work on a better
fix...
To take care of that I think maybe we could drop the cmd_mutex every
time we call audit_log_start. That's not necessarily going to be
pretty. Maybe make a new switch at the top of the function which knows
which operations we are going to have to allocate an audit_buffer. Drop
the lock, allocate the buffer, then retake the lock to finish running
audit_receive_msg()....
Maybe that second option isn't so hard and we can go directly
after that
instead of just dealing with userspace audit messages?
Thoughts?
Does it mean that we can also fix the problem only in the userspace?
Even if we fix userspace process (auditd, readahead-collector and systemd) only,
the problem would happen again if a new userspace audit process is implemented.
Therefore, I think we should fix only in the kernel.
Sorry, but I don't have clear method to fix it.
Regards,
Toshiyuki Okajima
8:45 p.m.
New subject: [PATCH 0/3] audit: remove audit_log_start() contention in AUDIT_USER type calls
There is a race condition between systemd and auditd:
systemd |auditd
-------------------------------------------+-----------------------------------
... |
-> audit_receive |...
-> mutex_lock(&audit_cmd_mutex) |-> audit_receive
... -> audit_log_start | -> mutex_lock(&audit_cmd_mutex)
-> wait_for_auditd | // wait for systemd
-> schedule_timeout(60*HZ) |
This fix will take care of systemd and anything USING audit. It still means
that we could race with something configuring audit and auditd shutting down.
The idea of dropping the lock at the top of audit_receive_msg() isn't as clean
as I had hoped, with AUDIT_ADD_RULE, AUDIT_TRIM, AUDIT_MAKE_EQUIV all
potentially allocating additional audit buffers indirectly through
trim_marked(). It may make sense to have trim_marked() send its queue through
a new thread.
Richard Guy Briggs (3):
selinux: call WARN_ONCE() instead of calling audit_log_start()
smack: call WARN_ONCE() instead of calling audit_log_start()
audit: drop audit_cmd_lock in AUDIT_USER family of cases
kernel/audit.c | 2 ++
security/selinux/ss/services.c | 12 ++++--------
security/smack/smack_lsm.c | 5 ++---
3 files changed, 8 insertions(+), 11 deletions(-)
1:15 a.m.
New subject: [RESEND][BUG][PATCH V3] audit: audit_log_start running on auditd should not stop
Hi.
Please apply this patch because the problem that audit_receive called by auditd
process is hung up by other process (systemd) which has already called it is fixed.
This patch fixes the problem that auditd hangs up by itself.
Thanks.
---
The backlog cannot be consumed when audit_log_start is running on auditd
even if audit_log_start calls wait_for_auditd to consume it.
The situation is the deadlock because only auditd can consume the backlog.
If the other process needs to send the backlog, it can be also stopped
by the deadlock.
So, audit_log_start running on auditd should not stop.
You can see the deadlock with the following reproducer:
# auditctl -a exit,always -S all
# reboot
Signed-off-by: Toshiyuki Okajima <toshi.okajima(a)jp.fujitsu.com>
Reviewed-by: gaofeng(a)cn.fujitsu.com
---
kernel/audit.c | 14 ++++++++------
1 files changed, 8 insertions(+), 6 deletions(-)
diff --git a/kernel/audit.c b/kernel/audit.c
index 7b0e23a..29cfc94 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1095,7 +1095,8 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx,
gfp_t gfp_mask,
struct audit_buffer *ab = NULL;
struct timespec t;
unsigned int uninitialized_var(serial);
- int reserve;
+ int reserve = 5; /* Allow atomic callers to go up to five
+ entries over the normal backlog limit */
unsigned long timeout_start = jiffies;
if (audit_initialized != AUDIT_INITIALIZED)
@@ -1104,11 +1105,12 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx,
gfp_t gfp_mask,
if (unlikely(audit_filter_type(type)))
return NULL;
- if (gfp_mask & __GFP_WAIT)
- reserve = 0;
- else
- reserve = 5; /* Allow atomic callers to go up to five
- entries over the normal backlog limit */
+ if (gfp_mask & __GFP_WAIT) {
+ if (audit_pid && audit_pid == current->pid)
+ gfp_mask &= ~__GFP_WAIT;
+ else
+ reserve = 0;
+ }
while (audit_backlog_limit
&& skb_queue_len(&audit_skb_queue) > audit_backlog_limit +
reserve) {
--
1.5.5.6
8:45 p.m.
New subject: [PATCH 1/3] selinux: call WARN_ONCE() instead of calling audit_log_start()
Two of the conditions in selinux_audit_rule_match() should never happen and
the third indicates a race that should be retried. Remove the calls to
audit_log() (which call audit_log_start()) and deal with the errors in the
caller, logging only once if the condition is met. Calling audit_log_start()
in this location makes buffer allocation and locking more complicated in the
calling tree (audit_filter_user()).
Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com>
---
security/selinux/ss/services.c | 12 ++++--------
1 files changed, 4 insertions(+), 8 deletions(-)
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index b4feecc..f4dda05 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -2938,25 +2938,21 @@ int selinux_audit_rule_match(u32 sid, u32 field, u32 op, void
*vrule,
struct selinux_audit_rule *rule = vrule;
int match = 0;
- if (!rule) {
- audit_log(actx, GFP_ATOMIC, AUDIT_SELINUX_ERR,
- "selinux_audit_rule_match: missing rule\n");
+ if (unlikely(!rule)) {
+ WARN_ONCE(1, "selinux_audit_rule_match: missing rule\n");
return -ENOENT;
}
read_lock(&policy_rwlock);
if (rule->au_seqno < latest_granting) {
- audit_log(actx, GFP_ATOMIC, AUDIT_SELINUX_ERR,
- "selinux_audit_rule_match: stale rule\n");
match = -ESTALE;
goto out;
}
ctxt = sidtab_search(&sidtab, sid);
- if (!ctxt) {
- audit_log(actx, GFP_ATOMIC, AUDIT_SELINUX_ERR,
- "selinux_audit_rule_match: unrecognized SID %d\n",
+ if (unlikely(!ctxt)) {
+ WARN_ONCE(1, "selinux_audit_rule_match: unrecognized SID %d\n",
sid);
match = -ENOENT;
goto out;
--
1.7.1
8:45 p.m.
New subject: [PATCH 2/3] smack: call WARN_ONCE() instead of calling audit_log_start()
Remove the call to audit_log() (which call audit_log_start()) and deal with
the errors in the caller, logging only once if the condition is met. Calling
audit_log_start() in this location makes buffer allocation and locking more
complicated in the calling tree (audit_filter_user()).
Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com>
---
security/smack/smack_lsm.c | 5 ++---
1 files changed, 2 insertions(+), 3 deletions(-)
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 8825375..185e2e7 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -3615,9 +3615,8 @@ static int smack_audit_rule_match(u32 secid, u32 field, u32 op, void
*vrule,
struct smack_known *skp;
char *rule = vrule;
- if (!rule) {
- audit_log(actx, GFP_ATOMIC, AUDIT_SELINUX_ERR,
- "Smack: missing rule\n");
+ if (unlikely(!rule)) {
+ WARN_ONCE(1, "Smack: missing rule\n");
return -ENOENT;
}
--
1.7.1
12:40 p.m.
New subject: [PATCH 2/3] smack: call WARN_ONCE() instead of calling audit_log_start()
On 12/4/2013 6:45 PM, Richard Guy Briggs wrote:
Remove the call to audit_log() (which call audit_log_start()) and
deal with
the errors in the caller, logging only once if the condition is met. Calling
audit_log_start() in this location makes buffer allocation and locking more
complicated in the calling tree (audit_filter_user()).
Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com>
I'm not opposed to this change, but have you actually tried it?
---
security/smack/smack_lsm.c | 5 ++---
1 files changed, 2 insertions(+), 3 deletions(-)
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 8825375..185e2e7 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -3615,9 +3615,8 @@ static int smack_audit_rule_match(u32 secid, u32 field, u32 op,
void *vrule,
struct smack_known *skp;
char *rule = vrule;
- if (!rule) {
- audit_log(actx, GFP_ATOMIC, AUDIT_SELINUX_ERR,
- "Smack: missing rule\n");
+ if (unlikely(!rule)) {
+ WARN_ONCE(1, "Smack: missing rule\n");
return -ENOENT;
}
4:17 p.m.
New subject: [PATCH 2/3] smack: call WARN_ONCE() instead of calling audit_log_start()
On Fri, Dec 06, 2013 at 10:40:56AM -0800, Casey Schaufler wrote:
On 12/4/2013 6:45 PM, Richard Guy Briggs wrote:
> Remove the call to audit_log() (which call audit_log_start()) and deal with
> the errors in the caller, logging only once if the condition is met. Calling
> audit_log_start() in this location makes buffer allocation and locking more
> complicated in the calling tree (audit_filter_user()).
>
> Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com>
I'm not opposed to this change, but have you actually tried it?
No, do you have concerns?
It is a projection based on the selinux_audit_match_rule() patch in the
same set.
> ---
> security/smack/smack_lsm.c | 5 ++---
> 1 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 8825375..185e2e7 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -3615,9 +3615,8 @@ static int smack_audit_rule_match(u32 secid, u32 field, u32
op, void *vrule,
> struct smack_known *skp;
> char *rule = vrule;
>
> - if (!rule) {
> - audit_log(actx, GFP_ATOMIC, AUDIT_SELINUX_ERR,
> - "Smack: missing rule\n");
> + if (unlikely(!rule)) {
> + WARN_ONCE(1, "Smack: missing rule\n");
> return -ENOENT;
> }
>
- RGB
--
Richard Guy Briggs <rbriggs(a)redhat.com>
Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat
Remote, Ottawa, Canada
Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545
8:45 p.m.
New subject: [PATCH 3/3] audit: drop audit_cmd_lock in AUDIT_USER family of cases
We do not need to hold the audit_cmd_mutex for this family of cases. The
possible exception to this is the call to audit_filter_user(), so drop the lock
immediately after. To help in fixing the race we are trying to avoid, make
sure that nothing called by audit_filter_user() calls audit_log_start(). In
particular, watch out for *_audit_rule_match().
This fix will take care of systemd and anything USING audit. It still means
that we could race with something configuring audit and auditd shutting down.
Signed-off-by: Richard Guy Briggs <rgb(a)tricolour.ca>
Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com>
---
kernel/audit.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)
diff --git a/kernel/audit.c b/kernel/audit.c
index 4689012..4cbc945 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -713,6 +713,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr
*nlh)
if (err)
break;
}
+ mutex_unlock(&audit_cmd_mutex);
audit_log_common_recv_msg(&ab, msg_type);
if (msg_type != AUDIT_USER_TTY)
audit_log_format(ab, " msg='%.1024s'",
@@ -729,6 +730,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr
*nlh)
}
audit_set_pid(ab, NETLINK_CB(skb).portid);
audit_log_end(ab);
+ mutex_lock(&audit_cmd_mutex);
}
break;
case AUDIT_ADD_RULE:
--
1.7.1
8:31 p.m.
New subject: [PATCH 3/3] audit: drop audit_cmd_lock in AUDIT_USER family of cases
On Wed, 4 Dec 2013 21:45:56 -0500
Richard Guy Briggs <rgb(a)redhat.com> wrote:
We do not need to hold the audit_cmd_mutex for this family of cases.
The
possible exception to this is the call to audit_filter_user(), so drop the lock
immediately after. To help in fixing the race we are trying to avoid, make
sure that nothing called by audit_filter_user() calls audit_log_start(). In
particular, watch out for *_audit_rule_match().
This fix will take care of systemd and anything USING audit. It still means
that we could race with something configuring audit and auditd shutting down.
Signed-off-by: Richard Guy Briggs <rgb(a)tricolour.ca>
Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com>
When I have tested a patch with my reproducer,
a hangup by this problem doesn't occur.
//// reproducer ////
# auditctl -a exit,always -S all
# reboot
/////////////////////////
So, this fix looks good to me.
Please add:
Reported-by: toshi.okajima(a)jp.fujitsu.com
Tested-by: toshi.okajima(a)jp.fujitsu.com
Thanks.
---
kernel/audit.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)
diff --git a/kernel/audit.c b/kernel/audit.c
index 4689012..4cbc945 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -713,6 +713,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr
*nlh)
if (err)
break;
}
+ mutex_unlock(&audit_cmd_mutex);
audit_log_common_recv_msg(&ab, msg_type);
if (msg_type != AUDIT_USER_TTY)
audit_log_format(ab, " msg='%.1024s'",
@@ -729,6 +730,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr
*nlh)
}
audit_set_pid(ab, NETLINK_CB(skb).portid);
audit_log_end(ab);
+ mutex_lock(&audit_cmd_mutex);
}
break;
case AUDIT_ADD_RULE:
--
1.7.1
--
Toshiyuki Okajima <toshi.okajima(a)jp.fujitsu.com>
4030
days inactive
4077
days old
linux-audit@lists.linux-audit.osci.io
13 comments
5 participants
participants (5)
-
Casey Schaufler -
Eric Paris -
Gao feng -
Richard Guy Briggs -
Toshiyuki Okajima