[PATCH] can: check for null sk before deferencing it via the call to sock_net

From: Colin King
Date: Fri Sep 08 2017 - 11:02:47 EST

From: Colin Ian King <colin.king@xxxxxxxxxxxxx>

The assignment of net via call sock_net will dereference sk. This
is performed before a sanity null check on sk, so there could be
a potential null dereference on the sock_net call if sk is null.
Fix this by assigning net after the sk null check. Also replace
the sk == NULL with the more usual !sk idiom.

Detected by CoverityScan CID#1431862 ("Dereference before null check")

Fixes: 384317ef4187 ("can: network namespace support for CAN_BCM protocol")
Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
net/can/bcm.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/can/bcm.c b/net/can/bcm.c
index 47a8748d953a..a3791674b8ce 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -1493,13 +1493,14 @@ static int bcm_init(struct sock *sk)
static int bcm_release(struct socket *sock)
struct sock *sk = sock->sk;
- struct net *net = sock_net(sk);
+ struct net *net;
struct bcm_sock *bo;
struct bcm_op *op, *next;

- if (sk == NULL)
+ if (!sk)
return 0;

+ net = sock_net(sk);
bo = bcm_sk(sk);

/* remove bcm_ops, timer, rx_unregister(), etc. */