Messages in this thread Patch in this message | | | Date | Fri, 11 Oct 2013 17:33:11 +0800 | From | Gao feng <> | Subject | Re: [BUG][PATCH][RFC] audit: hang up in audit_log_start executed on auditd |
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On 10/11/2013 09:36 AM, Toshiyuki Okajima wrote: > Hi. > > The following reproducer causes auditd daemon hang up. > (But the hang up is released after the audit_backlog_wait_time passes.) > # auditctl -a exit,always -S all > # reboot > > > I reproduced the hangup on KVM, and then got a crash dump. > After I analyzed the dump, I found auditd daemon hung up in audit_log_start. > (I have confirmed it on linux-3.12-rc4.) > > Like this: > crash> bt 1426 > PID: 1426 TASK: ffff88007b63e040 CPU: 1 COMMAND: "auditd" > #0 [ffff88007cb93918] __schedule at ffffffff8155d980 > #1 [ffff88007cb939b0] schedule at ffffffff8155de99 > #2 [ffff88007cb939c0] schedule_timeout at ffffffff8155b840 > #3 [ffff88007cb93a60] audit_log_start at ffffffff810d3ce5 > #4 [ffff88007cb93b20] audit_log_config_change at ffffffff810d3ece > #5 [ffff88007cb93b60] audit_receive_msg at ffffffff810d4fd6 > #6 [ffff88007cb93c00] audit_receive at ffffffff810d5173 > #7 [ffff88007cb93c30] netlink_unicast at ffffffff814c5269 > #8 [ffff88007cb93c90] netlink_sendmsg at ffffffff814c6386 > #9 [ffff88007cb93d20] sock_sendmsg at ffffffff814813c0 > #10 [ffff88007cb93e30] SYSC_sendto at ffffffff81481524 > #11 [ffff88007cb93f70] sys_sendto at ffffffff8148157e > #12 [ffff88007cb93f80] system_call_fastpath at ffffffff81568052 > RIP: 00007f5c47f7fba3 RSP: 00007fffcf21a118 RFLAGS: 00010202 > RAX: 000000000000002c RBX: ffffffff81568052 RCX: 0000000000000000 > RDX: 0000000000000030 RSI: 00007fffcf21e7d0 RDI: 0000000000000003 > RBP: 00007fffcf21e7d0 R8: 00007fffcf21a130 R9: 000000000000000c > R10: 0000000000000000 R11: 0000000000000293 R12: ffffffff8148157e > R13: ffff88007cb93f78 R14: 0000000000000020 R15: 0000000000000030 > ORIG_RAX: 000000000000002c CS: 0033 SS: 002b > > > The reason is that auditd daemon itself cannot consume its backlog > while audit_log_start is calling schedule_timeout on auditd daemon. > So, that is a deadlock! > > Therefore, I think audit_log_start shouldn't handle auditd's backlog > when auditd daemon executes audit_log_start. > > For example, I made the following fix patch. > -------------------------------------------------------------- > auditd daemon can execute the audit_log_start, and then it can cause > a hang up because only auditd daemon can consume the backlog. > So, audit_log_start executed by auditd daemon should not handle the backlog > in case auditd daemon hangs up (while wait_for_auditd is calling). > > Signed-off-by: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com> > --- > kernel/audit.c | 3 +++ > 1 files changed, 3 insertions(+), 0 deletions(-) > > diff --git a/kernel/audit.c b/kernel/audit.c > index 7b0e23a..86c389e 100644 > --- a/kernel/audit.c > +++ b/kernel/audit.c > @@ -1098,6 +1098,9 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, gfp_t gfp_mask, > int reserve; > unsigned long timeout_start = jiffies; > > + if (audit_pid && (audit_pid == current->pid)) > + return NULL; > +
audit_log_start can be called in interrupt context, such as iptables AUDIT module, we can't use current here. please try the patch below.
diff --git a/kernel/audit.c b/kernel/audit.c index 7b0e23a..1f35f3d 100644 --- a/kernel/audit.c +++ b/kernel/audit.c @@ -270,9 +270,13 @@ static int audit_log_config_change(char *function_name, int new, int old, int allow_changes) { struct audit_buffer *ab; + gfp_t gfp_mask = GFP_KERNEL; int rc = 0;
- ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE); + if (audit_pid && audit_pid == current->pid) + gfp_mask = GFP_ATOMIC; + + ab = audit_log_start(NULL, gfp_mask, AUDIT_CONFIG_CHANGE); if (unlikely(!ab)) return rc; audit_log_format(ab, "%s=%d old=%d", function_name, new, old);
Thanks
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