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Quentin Casasnovasdavem330
Quentin Casasnovas
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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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Diff for: net/rds/connection.c

-6
Original file line numberDiff line numberDiff line change
@@ -186,12 +186,6 @@ static struct rds_connection *__rds_conn_create(struct net *net,
186186
}
187187
}
188188

189-
if (trans == NULL) {
190-
kmem_cache_free(rds_conn_slab, conn);
191-
conn = ERR_PTR(-ENODEV);
192-
goto out;
193-
}
194-
195189
conn->c_trans = trans;
196190

197191
ret = trans->conn_alloc(conn, gfp);

Diff for: net/rds/send.c

+3-1
Original file line numberDiff line numberDiff line change
@@ -1013,11 +1013,13 @@ int rds_sendmsg(struct socket *sock, struct msghdr *msg, size_t payload_len)
10131013
release_sock(sk);
10141014
}
10151015

1016-
/* racing with another thread binding seems ok here */
1016+
lock_sock(sk);
10171017
if (daddr == 0 || rs->rs_bound_addr == 0) {
1018+
release_sock(sk);
10181019
ret = -ENOTCONN; /* XXX not a great errno */
10191020
goto out;
10201021
}
1022+
release_sock(sk);
10211023

10221024
if (payload_len > rds_sk_sndbuf(rs)) {
10231025
ret = -EMSGSIZE;

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