CVE-2022-50530

In the Linux kernel, the following vulnerability has been resolved:

blk-mq: fix null pointer dereference in blk_mq_clear_rq_mapping()

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().

Affected Software

References

• https://git.kernel.org/stable/c/6a440e6d04431e774dc084abe88c106e2a474c1a
• https://git.kernel.org/stable/c/76dd298094f484c6250ebd076fa53287477b2328