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

BugLink: https://bugs.launchpad.net/bugs/1835972
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/block/blk-core.c b/block/blk-core.c
index c5d5c8587770394dd4257882c3b1b72bed4f95c9..5eef1d9ee249bdfed3167e83bf631a2d85417e0f 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1083,6 +1083,7 @@ out_exit_flush_rq:
                q->exit_rq_fn(q, q->fq->flush_rq);
 out_free_flush_queue:
        blk_free_flush_queue(q->fq);
+       q->fq = NULL;
        return -ENOMEM;
 }
 EXPORT_SYMBOL(blk_init_allocated_queue);