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@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 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@xxxxxxxxxxxxx>
---
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
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