From 76dd298094f484c6250ebd076fa53287477b2328 Mon Sep 17 00:00:00 2001
From: Yu Kuai <yukuai3@huawei.com>
Date: Tue, 11 Oct 2022 22:22:53 +0800
Subject: [PATCH] blk-mq: fix null pointer dereference in
 blk_mq_clear_rq_mapping()
Git-commit: 76dd298094f484c6250ebd076fa53287477b2328
Patch-mainline: v6.1-rc2
References: git-fixes

Our syzkaller report a null pointer dereference, root cause is
Following: 

__blk_mq_alloc_map_and_rqs
 set->tags[hctx_idx] = blk_mq_alloc_map_and_rqs
  blk_mq_alloc_map_and_rqs
   blk_mq_alloc_rqs
    // failed due to oom
    alloc_pages_node
    // set->tags[hctx_idx] is still NULL
    blk_mq_free_rqs
     drv_tags = set->tags[hctx_idx];
     // null pointer dereference is triggered
     blk_mq_clear_rq_mapping(drv_tags, ...)

This is because commit 63064be150e4 ("blk-mq:
Add blk_mq_alloc_map_and_rqs()") merged the two steps:

1) set->tags[hctx_idx] = blk_mq_alloc_rq_map()
2) blk_mq_alloc_rqs(..., set->tags[hctx_idx])

into one step:

set->tags[hctx_idx] = blk_mq_alloc_map_and_rqs()

Since tags is not initialized yet in this case, fix the problem by
checking if tags is NULL pointer in blk_mq_clear_rq_mapping().

Fixes: 63064be150e4 ("blk-mq: Add blk_mq_alloc_map_and_rqs()")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: John Garry <john.garry@huawei.com>
Link: https://lore.kernel.org/r/20221011142253.4015966-1-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Coly Li <colyli@suse.de>

---
 block/blk-mq.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 8070b6c10e8d..33292c01875d 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3112,8 +3112,11 @@ static void blk_mq_clear_rq_mapping(struct blk_mq_tags *drv_tags,
 	struct page *page;
 	unsigned long flags;
 
-	/* There is no need to clear a driver tags own mapping */
-	if (drv_tags == tags)
+	/*
+	 * There is no need to clear mapping if driver tags is not initialized
+	 * or the mapping belongs to the driver tags.
+	 */
+	if (!drv_tags || drv_tags == tags)
 		return;
 
 	list_for_each_entry(page, &tags->page_list, lru) {
-- 
2.35.3