Re: [PATCH v2] audit: use proper refcount locking on audit_sock

On 2016-12-12 15:18, Paul Moore wrote: > On Mon, Dec 12, 2016 at 5:03 AM, Richard Guy Briggs <rgb(a)redhat.com&gt; wrote: > > Resetting audit_sock appears to be racy. > > > > audit_sock was being copied and dereferenced without using a refcount on > > the source sock. > > > > Bump the refcount on the underlying sock when we store a refrence in > > audit_sock and release it when we reset audit_sock. audit_sock > > modification needs the audit_cmd_mutex. > > > > See: https://lkml.org/lkml/2016/11/26/232 > > > > Thanks to Eric Dumazet <edumazet(a)google.com&gt; and Cong Wang > > <xiyou.wangcong(a)gmail.com&gt; on ideas how to fix it. > > > > Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com&gt; > > --- > > There has been a lot of change in the audit code that is about to go > > upstream to address audit queue issues. This patch is based on the > > source tree: git://git.infradead.org/users/pcmoore/audit#next > > --- > > kernel/audit.c | 34 ++++++++++++++++++++++++++++------ > > 1 files changed, 28 insertions(+), 6 deletions(-) > > diff --git a/kernel/audit.c b/kernel/audit.c > > index f20eee0..439f7f3 100644 > > --- a/kernel/audit.c > > +++ b/kernel/audit.c > > @@ -452,7 +452,9 @@ static void auditd_reset(void) > > struct sk_buff *skb; > > > > /* break the connection */ > > + sock_put(audit_sock); > > audit_pid = 0; > > + audit_nlk_portid = 0; > > audit_sock = NULL; > > > > /* flush all of the retry queue to the hold queue */ > > @@ -478,6 +480,12 @@ static int kauditd_send_unicast_skb(struct sk_buff *skb) > > if (rc >= 0) { > > consume_skb(skb); > > rc = 0; > > + } else { > > + if (rc & (-ENOMEM|-EPERM|-ECONNREFUSED)) { > > I dislike the way you wrote this because instead of simply looking at > this to see if it correct I need to sort out all the bits and find out > if there are other error codes that could run afoul of this check ... > make it simple, e.g. (rc == -ENOMEM || rc == -EPERM || ...). > Actually, since EPERM is 1, -EPERM (-1 in two's compliment is > 0xffffffff) is going to cause this to be true for pretty much any > value of rc, yes? Yes, you are correct. We need there a logical or on the results of each comparison to the return code rather than bit-wise or-ing the result codes together first to save a step. > > + mutex_lock(&audit_cmd_mutex); > > + auditd_reset(); > > + mutex_unlock(&audit_cmd_mutex); > > + } > > The code in audit#next handles netlink_unicast() errors in > kauditd_thread() and you are adding error handling code here in > kauditd_send_unicast_skb() ... that's messy. I don't care too much > where the auditd_reset() call is made, but let's only do it in one > function; FWIW, I originally put the error handling code in > kauditd_thread() because there was other error handling code that > needed to done in that scope so it resulted in cleaner code. Hmmm, I seem to remember it not returning the return code and I thought I had changed it to do so, but I see now that it was already there. Agreed, I needlessly duplicated that error handling. > Related, I see you are now considering ENOMEM to be a fatal condition, > that differs from the AUDITD_BAD macro in kauditd_thread(); this > difference needs to be reconciled. Also correct about -EPERM now that I check back to the intent of commit 32a1dbaece7e ("audit: try harder to send to auditd upon netlink failure") > Finally, you should update the comment header block for auditd_reset() > that it needs to be called with the audit_cmd_mutex held. Yup. > > @@ -1004,17 +1018,22 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh) > > return -EACCES; > > } > > if (audit_pid && new_pid && > > - audit_replace(requesting_pid) != -ECONNREFUSED) { > > + (audit_replace(requesting_pid) & (-ECONNREFUSED|-EPERM|-ENOMEM))) { > > Do we simply want to treat any error here as fatal, and not just > ECONN/EPERM/ENOMEM? If not, let's come up with a single macro to > handle the fatal netlink_unicast() return codes so we have some chance > to keep things consistent in the future. I'll work through this before I post another patch...

> paul moore - RGB