Re: [PATCH] RDS: fix race condition when sending a message on unbound socket.

From: santosh shilimkar
Date: Fri Oct 16 2015 - 13:48:06 EST


On 10/16/2015 8:11 AM, Quentin Casasnovas wrote:
Sasha's found a NULL pointer dereference in the RDS connection code when
sending a message to an apparently unbound socket. The problem is caused
by the code checking if the socket is bound in rds_sendmsg(), which checks
the rs_bound_addr field without taking a lock on the socket. This opens a
race where rs_bound_addr is temporarily set but where the transport is not
in rds_bind(), leading to a NULL pointer dereference when trying to
dereference 'trans' in __rds_conn_create().

Vegard wrote a reproducer for this issue, so kindly ask him to share if
you're interested.

I cannot reproduce the NULL pointer dereference using Vegard's reproducer
with this patch, whereas I could without.

Complete earlier incomplete fix to CVE-2015-6937:

74e98eb08588 ("RDS: verify the underlying transport exists before creating a connection")

Signed-off-by: Quentin Casasnovas <quentin.casasnovas@xxxxxxxxxx>
Reviewed-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Reviewed-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Cc: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Cc: Sasha Levin <sasha.levin@xxxxxxxxxx>
Cc: Chien Yen <chien.yen@xxxxxxxxxx>
Cc: Santosh Shilimkar <santosh.shilimkar@xxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
Looks right. Am glad that we got deference issue as well as
the bind race fixed with it. Mail sent to Vegard for his test
case which I would like to add to my tests. Thanks for the fix.

FWIW,
Acked-by: Santosh Shilimkar <santosh.shilimkar@xxxxxxxxxx>

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