block: blk_init_allocated_queue() set q->fq as NULL in the fail case

commit 54648cf1ec2d7f4b6a71767799c45676a138ca24 upstream.

We find the memory use-after-free issue in __blk_drain_queue()
on the kernel 4.14. After read the latest kernel 4.18-rc6 we
think it has the same problem.

Memory is allocated for q->fq in the blk_init_allocated_queue().
If the elevator init function called with error return, it will
run into the fail case to free the q->fq.

Then the __blk_drain_queue() uses the same memory after the free
of the q->fq, it will lead to the unpredictable event.

The patch is to set q->fq as NULL in the fail case of

Fixes: commit 7c94e1c157a2 ("block: introduce blk_flush_queue to drive flush machinery")
Cc: <>
Reviewed-by: Ming Lei <>
Reviewed-by: Bart Van Assche <>
Signed-off-by: xiao jin <>
Signed-off-by: Jens Axboe <>
[groeck: backport to v4.4.y/v4.9.y (context change)]
Signed-off-by: Guenter Roeck <>
Signed-off-by: Alessio Balsini <>
Signed-off-by: Greg Kroah-Hartman <>

1 file changed