On Wed, May 1, 2019 at 6:38 AM Guilherme G. Piccoli gpiccoli@canonical.com wrote:
Commit 37f9579f4c31 ("blk-mq: Avoid that submitting a bio concurrently with device removal triggers a crash") introduced a NULL pointer dereference in generic_make_request(). The patch sets q to NULL and enter_succeeded to false; right after, there's an 'if (enter_succeeded)' which is not taken, and then the 'else' will dereference q in blk_queue_dying(q).
This patch just moves the 'q = NULL' to a point in which it won't trigger the oops, although the semantics of this NULLification remains untouched.
A simple test case/reproducer is as follows: a) Build kernel v5.1-rc7 with CONFIG_BLK_CGROUP=n.
b) Create a raid0 md array with 2 NVMe devices as members, and mount it with an ext4 filesystem.
c) Run the following oneliner (supposing the raid0 is mounted in /mnt): (dd of=/mnt/tmp if=/dev/zero bs=1M count=999 &); sleep 0.3; echo 1 > /sys/block/nvme0n1/device/device/remove (whereas nvme0n1 is the 2nd array member)
This will trigger the following oops:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000078 PGD 0 P4D 0 Oops: 0000 [#1] SMP PTI RIP: 0010:generic_make_request+0x32b/0x400 Call Trace: submit_bio+0x73/0x140 ext4_io_submit+0x4d/0x60 ext4_writepages+0x626/0xe90 do_writepages+0x4b/0xe0 [...]
This patch has no functional changes and preserves the md/raid0 behavior when a member is removed before kernel v4.17.
Cc: Bart Van Assche bvanassche@acm.org Cc: stable@vger.kernel.org # v4.17 Fixes: 37f9579f4c31 ("blk-mq: Avoid that submitting a bio concurrently with device removal triggers a crash")
BTW, the legacy IO request path is removed since 5.0, the above fault commit can be removed as done by the following patches:
https://lore.kernel.org/linux-block/20190515030310.20393-1-ming.lei@redhat.c...
Signed-off-by: Guilherme G. Piccoli gpiccoli@canonical.com
block/blk-core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/block/blk-core.c b/block/blk-core.c index a55389ba8779..e21856a7f3fa 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -1076,7 +1076,6 @@ blk_qc_t generic_make_request(struct bio *bio) flags = BLK_MQ_REQ_NOWAIT; if (blk_queue_enter(q, flags) < 0) { enter_succeeded = false;
q = NULL; }
Please remove '{}'.
}@@ -1108,6 +1107,7 @@ blk_qc_t generic_make_request(struct bio *bio) bio_wouldblock_error(bio); else bio_io_error(bio);
q = NULL; } bio = bio_list_pop(&bio_list_on_stack[0]); } while (bio);-- 2.21.0
Reviewed-by: Ming Lei ming.lei@redhat.com
Thanks, Ming Lei