linux-kernel - Re: [PATCH net] rxrpc: Fix race between recvmsg and sendmsg on immediate call failure

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Date:   Thu, 30 Jul 2020 16:51:06 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     dhowells@...hat.com
Cc:     netdev@...r.kernel.org,
        syzbot+b54969381df354936d96@...kaller.appspotmail.com,
        marc.dionne@...istor.com, linux-afs@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] rxrpc: Fix race between recvmsg and sendmsg on
 immediate call failure

From: David Howells <dhowells@...hat.com>
Date: Wed, 29 Jul 2020 00:03:56 +0100

> There's a race between rxrpc_sendmsg setting up a call, but then failing to
> send anything on it due to an error, and recvmsg() seeing the call
> completion occur and trying to return the state to the user.
> 
> An assertion fails in rxrpc_recvmsg() because the call has already been
> released from the socket and is about to be released again as recvmsg deals
> with it.  (The recvmsg_q queue on the socket holds a ref, so there's no
> problem with use-after-free.)
> 
> We also have to be careful not to end up reporting an error twice, in such
> a way that both returns indicate to userspace that the user ID supplied
> with the call is no longer in use - which could cause the client to
> malfunction if it recycles the user ID fast enough.
> 
> Fix this by the following means:
 ...
> An oops like the following is produced:
 ...
> Fixes: 357f5ef64628 ("rxrpc: Call rxrpc_release_call() on error in rxrpc_new_client_call()")
> Reported-by: syzbot+b54969381df354936d96@...kaller.appspotmail.com
> Signed-off-by: David Howells <dhowells@...hat.com>
> Reviewed-by: Marc Dionne <marc.dionne@...istor.com>

Applied and queued up for -stable, thanks David.