block, bfq: fix bfqq uaf in bfq_limit_depth()
CVE: CVE-2024-53166
Component: kernel
CWE: CWE-416
Severity: Moderate
CVSS v3: 7.4/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
Release date: 2024-12-27T00:00:00+00:00

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

block, bfq: fix bfqq uaf in bfq_limit_depth()

Set new allocated bfqq to bic or remove freed bfqq from bic are both
protected by bfqd->lock, however bfq_limit_depth() is deferencing bfqq
from bic without the lock, this can lead to UAF if the io_context is
shared by multiple tasks.

For example, test bfq with io_uring can trigger following UAF in v6.6:

==================================================================
BUG: KASAN: slab-use-after-free in bfqq_group+0x15/0x50

Call Trace:
 <TASK>
 dump_stack_lvl+0x47/0x80
 print_address_description.constprop.0+0x66/0x300
 print_report+0x3e/0x70
 kasan_report+0xb4/0xf0
 bfqq_group+0x15/0x50
 bfqq_request_over_limit+0x130/0x9a0
 bfq_limit_depth+0x1b5/0x480
 __blk_mq_alloc_requests+0x2b5/0xa00
 blk_mq_get_new_requests+0x11d/0x1d0
 blk_mq_submit_bio+0x286/0xb00
 submit_bio_noacct_nocheck+0x331/0x400
 __block_write_full_folio+0x3d0/0x640
 writepage_cb+0x3b/0xc0
 write_cache_pages+0x254/0x6c0
 write_cache_pages+0x254/0x6c0
 do_writepages+0x192/0x310
 filemap_fdatawrite_wbc+0x95/0xc0
 __filemap_fdatawrite_range+0x99/0xd0
 filemap_write_and_wait_range.part.0+0x4d/0xa0
 blkdev_read_iter+0xef/0x1e0
 io_read+0x1b6/0x8a0
 io_issue_sqe+0x87/0x300
 io_wq_submit_work+0xeb/0x390
 io_worker_handle_work+0x24d/0x550
 io_wq_worker+0x27f/0x6c0
 ret_from_fork_asm+0x1b/0x30
 </TASK>

Allocated by task 808602:
 kasan_save_stack+0x1e/0x40
 kasan_set_track+0x21/0x30
 __kasan_slab_alloc+0x83/0x90
 kmem_cache_alloc_node+0x1b1/0x6d0
 bfq_get_queue+0x138/0xfa0
 bfq_get_bfqq_handle_split+0xe3/0x2c0
 bfq_init_rq+0x196/0xbb0
 bfq_insert_request.isra.0+0xb5/0x480
 bfq_insert_requests+0x156/0x180
 blk_mq_insert_request+0x15d/0x440
 blk_mq_submit_bio+0x8a4/0xb00
 submit_bio_noacct_nocheck+0x331/0x400
 __blkdev_direct_IO_async+0x2dd/0x330
 blkdev_write_iter+0x39a/0x450
 io_write+0x22a/0x840
 io_issue_sqe+0x87/0x300
 io_wq_submit_work+0xeb/0x390
 io_worker_handle_work+0x24d/0x550
 io_wq_worker+0x27f/0x6c0
 ret_from_fork+0x2d/0x50
 ret_from_fork_asm+0x1b/0x30

Freed by task 808589:
 kasan_save_stack+0x1e/0x40
 kasan_set_track+0x21/0x30
 kasan_save_free_info+0x27/0x40
 __kasan_slab_free+0x126/0x1b0
 kmem_cache_free+0x10c/0x750
 bfq_put_queue+0x2dd/0x770
 __bfq_insert_request.isra.0+0x155/0x7a0
 bfq_insert_request.isra.0+0x122/0x480
 bfq_insert_requests+0x156/0x180
 blk_mq_dispatch_plug_list+0x528/0x7e0
 blk_mq_flush_plug_list.part.0+0xe5/0x590
 __blk_flush_plug+0x3b/0x90
 blk_finish_plug+0x40/0x60
 do_writepages+0x19d/0x310
 filemap_fdatawrite_wbc+0x95/0xc0
 __filemap_fdatawrite_range+0x99/0xd0
 filemap_write_and_wait_range.part.0+0x4d/0xa0
 blkdev_read_iter+0xef/0x1e0
 io_read+0x1b6/0x8a0
 io_issue_sqe+0x87/0x300
 io_wq_submit_work+0xeb/0x390
 io_worker_handle_work+0x24d/0x550
 io_wq_worker+0x27f/0x6c0
 ret_from_fork+0x2d/0x50
 ret_from_fork_asm+0x1b/0x30

Fix the problem by protecting bic_to_bfqq() with bfqd->lock.

Statement: For triggering the bug, need to enable bfq that is disabled by default for Fedora. Also requires few conditions simultaneously (like usage of set limit_depth for bfq and io_uring), so the security impact is limited.

Remediation:
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
To mitigate this issue, prevent module bfq from being loaded (that would work for Fedora only). Please see https://access.redhat.com/solutions/41278 for how to blacklist a kernel module to prevent it from loading automatically.