netdev - Re: [PATCH net] rxrpc: Fix net namespace cleanup

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Date:   Tue, 30 Apr 2019 10:53:06 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     dhowells@...hat.com
Cc:     netdev@...r.kernel.org, linux-afs@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] rxrpc: Fix net namespace cleanup

From: David Howells <dhowells@...hat.com>
Date: Tue, 30 Apr 2019 08:34:08 +0100

> In rxrpc_destroy_all_calls(), there are two phases: (1) make sure the
> ->calls list is empty, emitting error messages if not, and (2) wait for the
> RCU cleanup to happen on outstanding calls (ie. ->nr_calls becomes 0).
> 
> To avoid taking the call_lock, the function prechecks ->calls and if empty,
> it returns to avoid taking the lock - this is wrong, however: it still
> needs to go and do the second phase and wait for ->nr_calls to become 0.
> 
> Without this, the rxrpc_net struct may get deallocated before we get to the
> RCU cleanup for the last calls.  This can lead to:
> 
>   Slab corruption (Not tainted): kmalloc-16k start=ffff88802b178000, len=16384
>   050: 6b 6b 6b 6b 6b 6b 6b 6b 61 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkakkkkkkk
> 
> Note the "61" at offset 0x58.  This corresponds to the ->nr_calls member of
> struct rxrpc_net (which is >9k in size, and thus allocated out of the 16k
> slab).
> 
> 
> Fix this by flipping the condition on the if-statement, putting the locked
> section inside the if-body and dropping the return from there.  The
> function will then always go on to wait for the RCU cleanup on outstanding
> calls.
> 
> Fixes: 2baec2c3f854 ("rxrpc: Support network namespacing")
> Signed-off-by: David Howells <dhowells@...hat.com>

Applied and queued up for -stable, thanks.