[PATCH] drbd: Add NULL check for net_conf to prevent dereference in state validation

[Mikhail Lobanov]

If the net_conf pointer is NULL and the code attempts to access its 
fields without a check, it will lead to a null pointer dereference.
Add a NULL check before dereferencing the pointer.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 44ed167da748 ("drbd: rcu_read_lock() and rcu_dereference() for tconn->net_conf")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Mikhail Lobanov <m.lobanov@xxxxxxxxxxxx>
---
 drivers/block/drbd/drbd_state.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/drbd/drbd_state.c b/drivers/block/drbd/drbd_state.c
index 287a8d1d3f70..87cf5883078f 100644
--- a/drivers/block/drbd/drbd_state.c
+++ b/drivers/block/drbd/drbd_state.c
@@ -876,7 +876,7 @@ is_valid_state(struct drbd_device *device, union drbd_state ns)
 		  ns.disk == D_OUTDATED)
 		rv = SS_CONNECTED_OUTDATES;
 
-	else if ((ns.conn == C_VERIFY_S || ns.conn == C_VERIFY_T) &&
+	else if (nc && (ns.conn == C_VERIFY_S || ns.conn == C_VERIFY_T) &&
 		 (nc->verify_alg[0] == 0))
 		rv = SS_NO_VERIFY_ALG;
 
-- 
2.43.0