linux-kernel - [PATCH 2/2] block: drbd: Fix a possible null-pointer dereference in is_valid

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Message-Id: <20190724034926.28755-1-baijiaju1990@gmail.com>
Date:   Wed, 24 Jul 2019 11:49:26 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     philipp.reisner@...bit.com, lars.ellenberg@...bit.com,
        axboe@...nel.dk
Cc:     drbd-dev@...ts.linbit.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jia-Ju Bai <baijiaju1990@...il.com>
Subject: [PATCH 2/2] block: drbd: Fix a possible null-pointer dereference in is_valid_state()

In is_valid_state(), there is an if statement on line 839 to check
whether nc is NULL:
    if (nc)

When nc is NULL, it is used on line 880:
    (nc->verify_alg[0] == 0)

Thus, a possible null-pointer dereference may occur.

To fix this bug, nc is also checked on line 880.

This bug is found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
---
 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 eeaa3b49b264..3cf477e9cf6a 100644
--- a/drivers/block/drbd/drbd_state.c
+++ b/drivers/block/drbd/drbd_state.c
@@ -877,7 +877,7 @@ is_valid_state(struct drbd_device *device, union drbd_state ns)
 		rv = SS_CONNECTED_OUTDATES;
 
 	else if ((ns.conn == C_VERIFY_S || ns.conn == C_VERIFY_T) &&
-		 (nc->verify_alg[0] == 0))
+		 (nc && nc->verify_alg[0] == 0))
 		rv = SS_NO_VERIFY_ALG;
 
 	else if ((ns.conn == C_VERIFY_S || ns.conn == C_VERIFY_T) &&
-- 
2.17.0