linux-kernel - [PATCH] blk-mq: fix null-ptr-deref in blk_mq_free

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Message-Id: <20250923070101.3507251-1-yukuai1@huaweicloud.com>
Date: Tue, 23 Sep 2025 15:01:01 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: axboe@...nel.dk,
	martin.petersen@...cle.com,
	hare@...e.de,
	ming.lei@...hat.com
Cc: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	yukuai3@...wei.com,
	yukuai1@...weicloud.com,
	yi.zhang@...wei.com,
	yangerkun@...wei.com,
	johnny.chenyi@...wei.com
Subject: [PATCH] blk-mq: fix null-ptr-deref in blk_mq_free_tags() from error path

From: Yu Kuai <yukuai3@...wei.com>

blk_mq_free_tags() can be called after blk_mq_init_tags(), while
tags->page_list is still not initialized, causing null-ptr-deref.

Fix this problem by initializing tags->page_list at blk_mq_init_tags(),
meanwhile, also free tags directly from error path because there is no
srcu barrier.

Fixes: ad0d05dbddc1 ("blk-mq: Defer freeing of tags page_list to SRCU callback")
Reported-by: syzbot+5c5d41e80248d610221f@...kaller.appspotmail.com
Closes: https://lore.kernel.org/all/68d1b079.a70a0220.1b52b.0000.GAE@google.com/
Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 block/blk-mq-tag.c | 9 +++++++++
 block/blk-mq.c     | 2 --
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index a63d21a4aab4..23f7731f19d1 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -569,6 +569,8 @@ struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
 	tags->nr_tags = total_tags;
 	tags->nr_reserved_tags = reserved_tags;
 	spin_lock_init(&tags->lock);
+	INIT_LIST_HEAD(&tags->page_list);
+
 	if (bt_alloc(&tags->bitmap_tags, depth, round_robin, node))
 		goto out_free_tags;
 	if (bt_alloc(&tags->breserved_tags, reserved_tags, round_robin, node))
@@ -606,6 +608,13 @@ void blk_mq_free_tags(struct blk_mq_tag_set *set, struct blk_mq_tags *tags)
 {
 	sbitmap_queue_free(&tags->bitmap_tags);
 	sbitmap_queue_free(&tags->breserved_tags);
+
+	/* if tags pages is not allocated yet, free tags directly */
+	if (list_empty(&tags->page_list)) {
+		kfree(tags);
+		return;
+	}
+
 	call_srcu(&set->tags_srcu, &tags->rcu_head, blk_mq_free_tags_callback);
 }
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 4ccf11cadf8c..09f579414161 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3582,8 +3582,6 @@ static int blk_mq_alloc_rqs(struct blk_mq_tag_set *set,
 	if (node == NUMA_NO_NODE)
 		node = set->numa_node;
 
-	INIT_LIST_HEAD(&tags->page_list);
-
 	/*
 	 * rq_size is the size of the request plus driver payload, rounded
 	 * to the cacheline size
-- 
2.39.2