Re: [PATCH] audit: fix memleak in auditd_send_unicast_skb.

[Paul Moore]

On Tue, Jul 18, 2017 at 2:37 AM,  <shuwang@xxxxxxxxxx> wrote:
> From: Shu Wang <shuwang@xxxxxxxxxx>
>
> Found this issue by kmemleak report, auditd_send_unicast_skb
> did not free skb if rcu_dereference(auditd_conn) returns null.
>
> unreferenced object 0xffff88082568ce00 (size 256):
> comm "auditd", pid 1119, jiffies 4294708499
> backtrace:
> [<ffffffff8176166a>] kmemleak_alloc+0x4a/0xa0
> [<ffffffff8121820c>] kmem_cache_alloc_node+0xcc/0x210
> [<ffffffff8161b99d>] __alloc_skb+0x5d/0x290
> [<ffffffff8113c614>] audit_make_reply+0x54/0xd0
> [<ffffffff8113dfa7>] audit_receive_msg+0x967/0xd70
> ----------------
> (gdb) list *audit_receive_msg+0x967
> 0xffffffff8113dff7 is in audit_receive_msg (kernel/audit.c:1133).
> 1132    skb = audit_make_reply(0, AUDIT_REPLACE, 0,
>                                 0, &pvnr, sizeof(pvnr));
> ---------------
> [<ffffffff8113e402>] audit_receive+0x52/0xa0
> [<ffffffff8166c561>] netlink_unicast+0x181/0x240
> [<ffffffff8166c8e2>] netlink_sendmsg+0x2c2/0x3b0
> [<ffffffff816112e8>] sock_sendmsg+0x38/0x50
> [<ffffffff816117a2>] SYSC_sendto+0x102/0x190
> [<ffffffff81612f4e>] SyS_sendto+0xe/0x10
> [<ffffffff8176d337>] entry_SYSCALL_64_fastpath+0x1a/0xa5
> [<ffffffffffffffff>] 0xffffffffffffffff
>
> Signed-off-by: Shu Wang <shuwang@xxxxxxxxxx>
> ---
>  kernel/audit.c | 1 +
>  1 file changed, 1 insertion(+)

Hello and thank you for the problem report, it is appreciated.  This
was also reported by Masami Ichikawa who provided a patch with the
correct fix (your patch does not catch any error conditions from
netlink_unicast()).

* https://www.redhat.com/archives/linux-audit/2017-July/msg00073.html

> diff --git a/kernel/audit.c b/kernel/audit.c
> index 833267b..6dd5569 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -641,6 +641,7 @@ static int auditd_send_unicast_skb(struct sk_buff *skb)
>         ac = rcu_dereference(auditd_conn);
>         if (!ac) {
>                 rcu_read_unlock();
> +               kfree_skb(skb);
>                 rc = -ECONNREFUSED;
>                 goto err;
>         }
> --
> 2.5.0

-- 
paul moore
www.paul-moore.com