CVE-2022-50488

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

block, bfq: fix possible uaf for 'bfqq->bic'

Our test report a uaf for 'bfqq->bic' in 5.10:

==================================================================

BUG: KASAN: use-after-free in bfq_select_queue+0x378/0xa30

CPU: 6 PID: 2318352 Comm: fsstress Kdump: loaded Not tainted 5.10.0-60.18.0.50.h602.kasan.eulerosv2r11.x86_64 #1

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58-20220320_160524-szxrtosci10000 04/01/2014

Call Trace:

bfq_select_queue+0x378/0xa30

bfq_dispatch_request+0xe8/0x130

blk_mq_do_dispatch_sched+0x62/0xb0

__blk_mq_sched_dispatch_requests+0x215/0x2a0

blk_mq_sched_dispatch_requests+0x8f/0xd0

__blk_mq_run_hw_queue+0x98/0x180

__blk_mq_delay_run_hw_queue+0x22b/0x240

blk_mq_run_hw_queue+0xe3/0x190

blk_mq_sched_insert_requests+0x107/0x200

blk_mq_flush_plug_list+0x26e/0x3c0

blk_finish_plug+0x63/0x90

__iomap_dio_rw+0x7b5/0x910

iomap_dio_rw+0x36/0x80

ext4_dio_read_iter+0x146/0x190 [ext4]

ext4_file_read_iter+0x1e2/0x230 [ext4]

new_sync_read+0x29f/0x400

vfs_read+0x24e/0x2d0

ksys_read+0xd5/0x1b0

do_syscall_64+0x33/0x40

entry_SYSCALL_64_after_hwframe+0x61/0xc6

Commit 3bc5e683c67d ("bfq: Split shared queues on move between cgroups")

changes that move process to a new cgroup will allocate a new bfqq to

use, however, the old bfqq and new bfqq can point to the same bic:

1) Initial state, two process with io in the same cgroup.

Process 1 Process 2

(BIC1) (BIC2)

| Λ | Λ

| | | |

V | V |

bfqq1 bfqq2

2) bfqq1 is merged to bfqq2.

Process 1 Process 2

(BIC1) (BIC2)

| |

\-------------\|

V

bfqq1 bfqq2(coop)

3) Process 1 exit, then issue new io(denoce IOA) from Process 2.

(BIC2)

| Λ

| |

V |

bfqq2(coop)

4) Before IOA is completed, move Process 2 to another cgroup and issue io.

Process 2

(BIC2)

Λ

|\--------------\

| V

bfqq2 bfqq3

Now that BIC2 points to bfqq3, while bfqq2 and bfqq3 both point to BIC2.

If all the requests are completed, and Process 2 exit, BIC2 will be

freed while there is no guarantee that bfqq2 will be freed before BIC2.

Fix the problem by clearing bfqq->bic while bfqq is detached from bic.