Re: [PATCH net-next v3] af_unix: Fix use-after-free crashes

On Fri, 2011-09-09 at 08:51 +0200, Eric Dumazet wrote:

Le jeudi 08 septembre 2011 à 01:37 -0700, Tim Chen a écrit :

quoted

On Thu, 2011-09-08 at 15:21 +0200, Eric Dumazet wrote:

quoted

Le jeudi 08 septembre 2011 à 11:59 +0200, Sedat Dilek a écrit :

quoted

I have tested this fixup patch on i386.
Can we have a separate patch with corrected descriptive text?

Thanks to all involved people.

Here it is :

[PATCH net-next v3] af_unix: Fix use-after-free crashes

Commit 0856a30409 (Scm: Remove unnecessary pid & credential references
in Unix socket's send and receive path) introduced an use-after-free
bug.

We are allowed to steal the references to pid/cred only in the last skb
sent from unix_stream_sendmsg(), because first skbs might be consumed by
the receiver before we finish our sendmsg() call.

Remove scm_release() helper, since its cleaner to clear pid/cred fields
in unix_scm_to_skb() when we steal them.

Based on prior patches from Yan Zheng and Tim Chen

Signed-off-by: Eric Dumazet <redacted>
Reported-by: Jiri Slaby <redacted>
Tested-by: Sedat Dilek <redacted>
Tested-by: Valdis Kletnieks <redacted>
---

Thanks.

Acked-by: Tim Chen <redacted>

Now we have to fix a bug in unix_stream_recvmsg() as well.

Thanks for your careful review to catch the bugs.  Wish I had thought
about the stream msg case more in my original patch.

consume_skb() call actually releases pid/cred references, and we can use
them after their eventual freeing.

Keep also in mind that receiver can provides a too short user buffer,
and skb can be put back to head of sk_receive_queue

Tim, your 0856a304091b33 commit introduced a lot of bugs, I was right
asking a revert.

If we revert your patch, my litle patch (af_unix: dont send
SCM_CREDENTIALS by default) is enough to solve performance problems.

But the regression where we do send SCM_CREDENTIALS is not addressed,
right?  I don't mind reverting my patch if there's a better solution.

Tim