[PATCH] md: raid0/linear: fix dereference before null check on pointer mddev

[PATCH] md: raid0/linear: fix dereference before null check on pointer mddev

[Colin King]

From: Colin Ian King <colin.king@canonical.com>

Pointer mddev is being dereferenced with a test_bit call before mddev
is being null checked, this may cause a null pointer dereference. Fix
this by moving the null pointer checks to sanity check mddev before
it is dereferenced.

Addresses-Coverity: ("Dereference before null check")
Fixes: 62f7b1989c02 ("md raid0/linear: Mark array as 'broken' and fail BIOs if a member is gone")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 drivers/md/md.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 8bb69c61afe0..49452149ac72 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -470,17 +470,18 @@ static blk_qc_t md_submit_bio(struct bio *bio)
 	struct mddev *mddev = bio->bi_disk->private_data;
 	unsigned int sectors;
 
-	if (unlikely(test_bit(MD_BROKEN, &mddev->flags)) && (rw == WRITE)) {
+	if (mddev == NULL || mddev->pers == NULL) {
 		bio_io_error(bio);
 		return BLK_QC_T_NONE;
 	}
 
-	blk_queue_split(&bio);
-
-	if (mddev == NULL || mddev->pers == NULL) {
+	if (unlikely(test_bit(MD_BROKEN, &mddev->flags)) && (rw == WRITE)) {
 		bio_io_error(bio);
 		return BLK_QC_T_NONE;
 	}
+
+	blk_queue_split(&bio);
+
 	if (mddev->ro == 1 && unlikely(rw == WRITE)) {
 		if (bio_sectors(bio) != 0)
 			bio->bi_status = BLK_STS_IOERR;
-- 
2.27.0

Re: [PATCH] md: raid0/linear: fix dereference before null check on pointer mddev

[Guilherme Piccoli]

Great catch Colin, thanks!
Feel free to add my:

Reviewed-by: Guilherme G. Piccoli <gpiccoli@canonical.com>


P.S.  Not sure if it's only me, but the diff is soo much easier to
read when git is set to use patience diff algorithm:
https://termbin.com/f8ig

Re: [PATCH] md: raid0/linear: fix dereference before null check on pointer mddev

[Song Liu]

On Thu, Jul 2, 2020 at 7:41 AM Guilherme Piccoli <gpiccoli@canonical.com> wrote:
>
> Great catch Colin, thanks!
> Feel free to add my:
>
> Reviewed-by: Guilherme G. Piccoli <gpiccoli@canonical.com>

Thanks Colin and Guilherme! Applied to md-next.

>
>
> P.S.  Not sure if it's only me, but the diff is soo much easier to
> read when git is set to use patience diff algorithm:
> https://termbin.com/f8ig

Agreed. Patience is cleaner.