2019-07-24 03:50:59

by Jia-Ju Bai

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 <[email protected]>
---
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

2019-07-24 11:39:11

by Roland Kammerer

Subject: Re: [Drbd-dev] [PATCH 2/2] block: drbd: Fix a possible null-pointer dereference in is_valid_state()

On Wed, Jul 24, 2019 at 11:49:26AM +0800, Jia-Ju Bai wrote:
> 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 <[email protected]>
> ---
> 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;

AFAIK it is "impossible" to reach such a DRBD state without having a
valid net conf. Anyways, a check is a good idea, but the logic is wrong,
I would propose something like this:

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;

Regards, rck