CVE-2022-50488 — linux / linux_kernel
Use After FreeIn 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:
- Initial state, two process with io in the same cgroup.
Process 1 Process 2 (BIC1) (BIC2) | Λ | Λ | | | | V | V | bfqq1 bfqq2
- bfqq1 is merged to bfqq2.
Process 1 Process 2 (BIC1) (BIC2) | | -------------| V bfqq1 bfqq2(coop)
- Process 1 exit, then issue new io(denoce IOA) from Process 2.
(BIC2) | Λ | | V | bfqq2(coop)
- 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.
| Software | From | Fixed in |
|---|---|---|
| linux / linux_kernel | 5.4.198 | 5.5 |
| linux / linux_kernel | 5.10.121 | 5.10.175 |
| linux / linux_kernel | 5.15.46 | 5.15.86 |
| linux / linux_kernel | 5.17.14 | 5.18 |
| linux / linux_kernel | 5.18.3 | 6.0.16 |
| linux / linux_kernel | 6.1 | 6.1.2 |
- https://git.kernel.org/stable/c/094f3d9314d67691cb21ba091c1b528f6e3c4893
- https://git.kernel.org/stable/c/5533742c7cb1bc9b1f0bf401cc397d44a3a9e07a
- https://git.kernel.org/stable/c/64dc8c732f5c2b406cc752e6aaa1bd5471159cab
- https://git.kernel.org/stable/c/761564d93c8265f65543acf0a576b32d66bfa26a
- https://git.kernel.org/stable/c/b22fd72bfebda3956efc4431b60ddfc0a51e03e0
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