linux-kernel - Re: [PATCH net] rxrpc: Fix service call disconnection

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Date:   Fri, 07 Feb 2020 11:21:54 +0100 (CET)
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 service call disconnection

From: David Howells <dhowells@...hat.com>
Date: Thu, 06 Feb 2020 13:55:01 +0000

> The recent patch that substituted a flag on an rxrpc_call for the
> connection pointer being NULL as an indication that a call was disconnected
> puts the set_bit in the wrong place for service calls.  This is only a
> problem if a call is implicitly terminated by a new call coming in on the
> same connection channel instead of a terminating ACK packet.
> 
> In such a case, rxrpc_input_implicit_end_call() calls
> __rxrpc_disconnect_call(), which is now (incorrectly) setting the
> disconnection bit, meaning that when rxrpc_release_call() is later called,
> it doesn't call rxrpc_disconnect_call() and so the call isn't removed from
> the peer's error distribution list and the list gets corrupted.
> 
> KASAN finds the issue as an access after release on a call, but the
> position at which it occurs is confusing as it appears to be related to a
> different call (the call site is where the latter call is being removed
> from the error distribution list and either the next or pprev pointer
> points to a previously released call).
> 
> Fix this by moving the setting of the flag from __rxrpc_disconnect_call()
> to rxrpc_disconnect_call() in the same place that the connection pointer
> was being cleared.
> 
> Fixes: 5273a191dca6 ("rxrpc: Fix NULL pointer deref due to call->conn being cleared on disconnect")
> Signed-off-by: David Howells <dhowells@...hat.com>

Applied and queued up for -stable.