[RFC PATCH v3] audit: use proper refcount locking on audit_sock
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> and Cong Wang
<xiyou.wangcong(a)gmail.com> on ideas how to fix it.
Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com>
---
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 | 28 +++++++++++++++++++++++-----
1 files changed, 23 insertions(+), 5 deletions(-)
diff --git a/kernel/audit.c b/kernel/audit.c
index f20eee0..3bb4126 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -446,14 +446,19 @@ static void kauditd_retry_skb(struct sk_buff *skb)
* Description:
* Break the auditd/kauditd connection and move all the records in the retry
* queue into the hold queue in case auditd reconnects.
+ * The audit_cmd_mutex must be held when calling this function.
*/
static void auditd_reset(void)
{
struct sk_buff *skb;
/* break the connection */
+ if (audit_sock) {
+ sock_put(audit_sock);
+ audit_sock = NULL;
+ }
audit_pid = 0;
- audit_sock = NULL;
+ audit_nlk_portid = 0;
/* flush all of the retry queue to the hold queue */
while ((skb = skb_dequeue(&audit_retry_queue)))
@@ -579,7 +584,9 @@ static int kauditd_thread(void *dummy)
auditd = 0;
if (AUDITD_BAD(rc, reschedule)) {
+ mutex_lock(&audit_cmd_mutex);
auditd_reset();
+ mutex_unlock(&audit_cmd_mutex);
reschedule = 0;
}
} else
@@ -594,7 +601,9 @@ static int kauditd_thread(void *dummy)
auditd = 0;
if (AUDITD_BAD(rc, reschedule)) {
kauditd_hold_skb(skb);
+ mutex_lock(&audit_cmd_mutex);
auditd_reset();
+ mutex_unlock(&audit_cmd_mutex);
reschedule = 0;
} else
/* temporary problem (we hope), queue
@@ -623,7 +632,9 @@ quick_loop:
if (rc) {
auditd = 0;
if (AUDITD_BAD(rc, reschedule)) {
+ mutex_lock(&audit_cmd_mutex);
auditd_reset();
+ mutex_unlock(&audit_cmd_mutex);
reschedule = 0;
}
@@ -1010,11 +1021,16 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr
*nlh)
}
if (audit_enabled != AUDIT_OFF)
audit_log_config_change("audit_pid", new_pid, audit_pid, 1);
- audit_pid = new_pid;
- audit_nlk_portid = NETLINK_CB(skb).portid;
- audit_sock = skb->sk;
- if (!new_pid)
+ if (new_pid) {
+ if (audit_sock)
+ sock_put(audit_sock);
+ audit_pid = new_pid;
+ audit_nlk_portid = NETLINK_CB(skb).portid;
+ sock_hold(skb->sk);
+ audit_sock = skb->sk;
+ } else {
auditd_reset();
+ }
wake_up_interruptible(&kauditd_wait);
}
if (s.mask & AUDIT_STATUS_RATE_LIMIT) {
@@ -1283,8 +1299,10 @@ static void __net_exit audit_net_exit(struct net *net)
{
struct audit_net *aunet = net_generic(net, audit_net_id);
struct sock *sock = aunet->nlsk;
+ mutex_lock(&audit_cmd_mutex);
if (sock == audit_sock)
auditd_reset();
+ mutex_unlock(&audit_cmd_mutex);
RCU_INIT_POINTER(aunet->nlsk, NULL);
synchronize_net();
--
1.7.1