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RDS: fix race condition when sending a message on unbound socket
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: 74e98eb ("RDS: verify the underlying transport exists before creating a connection") Cc: David S. Miller <firstname.lastname@example.org> Cc: email@example.com Reviewed-by: Vegard Nossum <firstname.lastname@example.org> Reviewed-by: Sasha Levin <email@example.com> Acked-by: Santosh Shilimkar <firstname.lastname@example.org> Signed-off-by: Quentin Casasnovas <email@example.com> Signed-off-by: David S. Miller <firstname.lastname@example.org>
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