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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 <davem@davemloft.net>
Cc: stable@vger.kernel.org

Reviewed-by: Vegard Nossum <vegard.nossum@oracle.com>
Reviewed-by: Sasha Levin <sasha.levin@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Quentin Casasnovas authored and davem330 committed Nov 24, 2015
1 parent 20f7956 commit 8c7188b23474cca017b3ef354c4a58456f68303a
Showing with 3 additions and 7 deletions.
  1. +0 −6 net/rds/connection.c
  2. +3 −1 net/rds/send.c
View
@@ -186,12 +186,6 @@ static struct rds_connection *__rds_conn_create(struct net *net,
}
}
if (trans == NULL) {
kmem_cache_free(rds_conn_slab, conn);
conn = ERR_PTR(-ENODEV);
goto out;
}
conn->c_trans = trans;
ret = trans->conn_alloc(conn, gfp);
View
@@ -1013,11 +1013,13 @@ int rds_sendmsg(struct socket *sock, struct msghdr *msg, size_t payload_len)
release_sock(sk);
}
/* racing with another thread binding seems ok here */
lock_sock(sk);
if (daddr == 0 || rs->rs_bound_addr == 0) {
release_sock(sk);
ret = -ENOTCONN; /* XXX not a great errno */
goto out;
}
release_sock(sk);
if (payload_len > rds_sk_sndbuf(rs)) {
ret = -EMSGSIZE;

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