From e2f3d50558b8e5deeaacf4990e478fc844444de5 Mon Sep 17 00:00:00 2001 From: Quentin Casasnovas Date: Tue, 24 Nov 2015 17:13:21 -0500 Subject: [PATCH] RDS: fix race condition when sending a message on unbound socket commit 8c7188b23474cca017b3ef354c4a58456f68303a upstream. 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") Reviewed-by: Vegard Nossum Reviewed-by: Sasha Levin Acked-by: Santosh Shilimkar Signed-off-by: Quentin Casasnovas Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- 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 e88bf3976e54..642ad42c416b 100644 --- a/net/rds/connection.c +++ b/net/rds/connection.c @@ -177,12 +177,6 @@ static struct rds_connection *__rds_conn_create(__be32 laddr, __be32 faddr, } } - 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 88eace57dd6b..31c9fa464b11 100644 --- a/net/rds/send.c +++ b/net/rds/send.c @@ -955,11 +955,13 @@ int rds_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg, 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); /* size of rm including all sgs */ ret = rds_rm_size(msg, payload_len); -- 2.20.1