From: xiao jin jin.xiao@intel.com

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 blk_init_allocated_queue().

Fixes: commit 7c94e1c157a2 ("block: introduce blk_flush_queue to drive flush machinery") Cc: stable@vger.kernel.org Reviewed-by: Ming Lei ming.lei@redhat.com Reviewed-by: Bart Van Assche bart.vanassche@wdc.com Signed-off-by: xiao jin jin.xiao@intel.com Signed-off-by: Jens Axboe axboe@kernel.dk [groeck: backport to v4.4.y/v4.9.y (context change)] Signed-off-by: Guenter Roeck linux@roeck-us.net --- This patch was not applied to v4.4.y and v4.9.y due to a context conflict. See https://lore.kernel.org/stable/1536310209129100@kroah.com/ and https://lore.kernel.org/stable/153631018011582@kroah.com/ for details. It was applied to v4.14.y and to v4.18.y.

Please consider applying this backport. It is relevant because it fixes CVE-2018-20856.

Thanks, Guenter

block/blk-core.c | 1 + 1 file changed, 1 insertion(+)

diff --git a/block/blk-core.c b/block/blk-core.c index 50d77c90070d..7662f97dded6 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -870,6 +870,7 @@ blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,

fail: blk_free_flush_queue(q->fq); + q->fq = NULL; return NULL; } EXPORT_SYMBOL(blk_init_allocated_queue);