Re: [PATCH] audit: fix memleak in auditd_send_unicast_skb.
----- Original Message -----
From: "Paul Moore" <paul(a)paul-moore.com>
To: shuwang(a)redhat.com
Cc: "Eric Paris" <eparis(a)redhat.com>, linux-audit(a)redhat.com,
linux-kernel(a)vger.kernel.org, liwang(a)redhat.com,
chuhu(a)redhat.com
Sent: Tuesday, July 18, 2017 8:21:05 PM
Subject: Re: [PATCH] audit: fix memleak in auditd_send_unicast_skb.
On Tue, Jul 18, 2017 at 2:37 AM, <shuwang(a)redhat.com> wrote:
> From: Shu Wang <shuwang(a)redhat.com>
>
> 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(a)redhat.com>
> ---
> 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()).
netlink_unicast has it's error handling, and is responsible for
releasing skb. so the Masami Ichikawa's fix may cause double
free problems.
1274 int netlink_unicast(struct sock *ssk, struct sk_buff *skb,
1275 >--->--- u32 portid, int nonblock)
1276 {
......
1285 >---sk = netlink_getsockbyportid(ssk, portid);
1286 >---if (IS_ERR(sk)) {
1287 >--->---kfree_skb(skb);
1288 >--->---return PTR_ERR(sk);
1289 >---}
......
1293 >---if (sk_filter(sk, skb)) {
1294 >--->---err = skb->len;
1295 >--->---kfree_skb(skb);
1296 >--->---sock_put(sk);
1297 >--->---return err;
1298 >---}
* 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