The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 93decc563637c4288380912eac0eb42fb246cc04 Mon Sep 17 00:00:00 2001

From: Kevin Vigor kvigor@gmail.com Date: Fri, 6 Nov 2020 14:20:34 -0800 Subject: [PATCH] md/raid10: initialize r10_bio->read_slot before use.

In __make_request() a new r10bio is allocated and passed to raid10_read_request(). The read_slot member of the bio is not initialized, and the raid10_read_request() uses it to index an array. This leads to occasional panics.

Fix by initializing the field to invalid value and checking for valid value in raid10_read_request().

Cc: stable@vger.kernel.org Signed-off-by: Kevin Vigor kvigor@gmail.com Signed-off-by: Song Liu songliubraving@fb.com

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c index b7bca6703df8..3153183b7772 100644 --- a/drivers/md/raid10.c +++ b/drivers/md/raid10.c @@ -1127,7 +1127,7 @@ static void raid10_read_request(struct mddev *mddev, struct bio *bio, struct md_rdev *err_rdev = NULL; gfp_t gfp = GFP_NOIO;

- if (r10_bio->devs[slot].rdev) { + if (slot >= 0 && r10_bio->devs[slot].rdev) { /* * This is an error retry, but we cannot * safely dereference the rdev in the r10_bio, @@ -1508,6 +1508,7 @@ static void __make_request(struct mddev *mddev, struct bio *bio, int sectors) r10_bio->mddev = mddev; r10_bio->sector = bio->bi_iter.bi_sector; r10_bio->state = 0; + r10_bio->read_slot = -1; memset(r10_bio->devs, 0, sizeof(r10_bio->devs[0]) * conf->geo.raid_disks);

if (bio_data_dir(bio) == READ)