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* [PATCH 1/2] block: Fix a NULL pointer dereference in  generic_make_request()
@ 2019-04-30 22:37 Guilherme G. Piccoli
  2019-04-30 22:37 ` [PATCH 2/2] md/raid0: Do not bypass blocking queue entered for raid0 bios Guilherme G. Piccoli
                   ` (3 more replies)
  0 siblings, 4 replies; 17+ messages in thread
From: Guilherme G. Piccoli @ 2019-04-30 22:37 UTC (permalink / raw)
  To: linux-block, linux-raid
  Cc: dm-devel, axboe, gavin.guo, jay.vosburgh, gpiccoli, kernel,
	Bart Van Assche, stable

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")
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;
 			}
 		}
 
@@ -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


^ permalink raw reply related	[flat|nested] 17+ messages in thread

end of thread, other threads:[~2019-05-20 19:26 UTC | newest]

Thread overview: 17+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-04-30 22:37 [PATCH 1/2] block: Fix a NULL pointer dereference in generic_make_request() Guilherme G. Piccoli
2019-04-30 22:37 ` [PATCH 2/2] md/raid0: Do not bypass blocking queue entered for raid0 bios Guilherme G. Piccoli
2019-05-06 16:50   ` Song Liu
2019-05-06 18:48     ` Guilherme G. Piccoli
2019-05-06 21:07       ` Song Liu
2019-05-07 21:51         ` Guilherme G. Piccoli
2019-05-08  9:29         ` Wols Lists
2019-05-08 14:52           ` Guilherme G. Piccoli
2019-05-08 16:52             ` Wols Lists
2019-05-17 16:19               ` Guilherme G. Piccoli
2019-05-20 16:23                 ` Song Liu
2019-05-20 19:25                   ` Guilherme Piccoli
2019-04-30 22:55 ` [PATCH 1/2] block: Fix a NULL pointer dereference in generic_make_request() Bart Van Assche
2019-05-17  3:33 ` Eric Ren
2019-05-17 16:17   ` Guilherme G. Piccoli
2019-05-20  2:43     ` Eric Ren
2019-05-17 22:04 ` Ming Lei

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