linux-kernel - Re: [BUG][PATCH V3] audit: audit_log_start running on auditd should not stop

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Date:	Tue, 15 Oct 2013 17:41:02 +0800
From:	Gao feng <gaofeng@...fujitsu.com>
To:	Toshiyuki Okajima <toshi.okajima@...fujitsu.com>
CC:	viro@...iv.linux.org.uk, eparis@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG][PATCH V3] audit: audit_log_start running on auditd should
 not stop

On 10/15/2013 03:58 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 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@...fujitsu.com>
> Cc: gaofeng@...fujitsu.com
> ---
>  kernel/audit.c |   14 ++++++++------
>  1 files changed, 8 insertions(+), 6 deletions(-)
> 

Looks good to me, thanks!
Reviewed-by: Gao feng <gaofeng@...fujitsu.com>


> 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) {
> 

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