From 8e92c2b0cb50a31e2956760498bc8cdb72993fb3 Mon Sep 17 00:00:00 2001 From: Quentin Casasnovas Date: Fri, 16 Oct 2015 17:11:42 +0200 Subject: [PATCH] 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: 74e98eb08588 ("RDS: verify the underlying transport exists before creating a connection") Signed-off-by: Quentin Casasnovas Reviewed-by: Vegard Nossum Reviewed-by: Sasha Levin Cc: Vegard Nossum Cc: Sasha Levin Cc: Chien Yen Cc: Santosh Shilimkar Cc: David S. Miller Cc: stable@vger.kernel.org --- net/rds/connection.c | 6 ------ net/rds/send.c | 4 +++- 2 files changed, 3 insertions(+), 7 deletions(-) diff --git a/net/rds/connection.c b/net/rds/connection.c index 49adeef8090c..9b2de5e67d79 100644 --- a/net/rds/connection.c +++ b/net/rds/connection.c @@ -190,12 +190,6 @@ new_conn: } } - 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); diff --git a/net/rds/send.c b/net/rds/send.c index 4df61a515b83..859de6f32521 100644 --- a/net/rds/send.c +++ b/net/rds/send.c @@ -1009,11 +1009,13 @@ 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; -- 2.4.3