[PATCH v3] md/raid5: reject raid4/5 arrays with too few disks

["Chen Cheng" <chencheng@fnnas.com>]

From: Chen Cheng <chencheng@fnnas.com>

raid4 and raid5 require at least two disks, while raid6 requires at least
four disks. setup_conf() only rejects raid6 arrays with fewer than four
disks. As a result, an invalid raid4 or raid5 array can be assembled with
no data disks and later reach raid5_set_limits().

Reject such arrays before the r5conf is created. This prevents the invalid
geometry from reaching queue limit setup, where roundup_pow_of_two() can be
called with a zero stripe size.

Reported-by: syzbot+de94ddbfff0c9e6fe030@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/r/6a778c82.01d0871a.3a0d52.006a.GAE@google.com/
Fixes: f63f17350e53 ("md/raid5: use the atomic queue limit update APIs")
Signed-off-by: Chen Cheng <chencheng@fnnas.com>
---
v1->v2:
- Fix wrong tags
- Check raid-4 also

v2->v3:
- Keep two-disk raid5 arrays valid by rejecting raid4/5 only below two disks
---
 drivers/md/raid5.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index b91545ce090d..e1f20035703b 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -7655,13 +7655,15 @@ static struct r5conf *setup_conf(struct mddev *mddev)
 	     && !algorithm_valid_raid6(mddev->new_layout))) {
 		pr_warn("md/raid:%s: layout %d not supported\n",
 			mdname(mddev), mddev->new_layout);
 		return ERR_PTR(-EIO);
 	}
-	if (mddev->new_level == 6 && mddev->raid_disks < 4) {
-		pr_warn("md/raid:%s: not enough configured devices (%d, minimum 4)\n",
-			mdname(mddev), mddev->raid_disks);
+	if ((mddev->new_level != 6 && mddev->raid_disks < 2) ||
+	    (mddev->new_level == 6 && mddev->raid_disks < 4)) {
+		pr_warn("md/raid:%s: not enough configured devices (%d, minimum %d)\n",
+			mdname(mddev), mddev->raid_disks,
+			mddev->new_level == 6 ? 4 : 2);
 		return ERR_PTR(-EINVAL);
 	}
 
 	if (!mddev->new_chunk_sectors ||
 	    (mddev->new_chunk_sectors << 9) % PAGE_SIZE ||
-- 
2.55.0