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.
CVSS Details
- CVSS 3.1 Base Score: 7.8
- CVSS 3.1 Vector: (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
Covered by Rapid7
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Amazon Linux Ami 2 | — | Upgrade bpftool-debuginfoUpgrade kernel-livepatch-5.10.176-157.645Upgrade kernel-headersUpgrade kernel-tools-debuginfoUpgrade perf-debuginfoUpgrade perfUpgrade kernel-livepatch-5.15.86-53.137Upgrade kernel-toolsUpgrade python-perfUpgrade kernel-debuginfo-common-aarch64Upgrade bpftoolUpgrade kernel-debuginfo-common-x86_64Upgrade kernel-develUpgrade python-perf-debuginfoUpgrade kernel-tools-develUpgrade kernel-debuginfoUpgrade kernel | May 20, 2026 | May 20, 2026 |
| Debian | — | Upgrade linux | Oct 6, 2025 | Oct 6, 2025 |
| Huawei Euleros 2_0_sp13 | — | Upgrade bpftoolUpgrade python3-perfUpgrade kernel-tools-libsUpgrade kernelUpgrade kernel-abi-stablelistsUpgrade kernel-tools | Feb 3, 2026 | Feb 2, 2026 |
| Redhat_linux | — | No solution exists | Jul 17, 2026 | Oct 4, 2025 |
| Ubuntu | — | Upgrade linux-gkeUpgrade linux-gcpUpgrade linux-intel-iot-realtimeUpgrade linux-riscv-5.15Upgrade linuxUpgrade linux-awsUpgrade linux-nvidia-tegra-5.15Upgrade linux-gkeopUpgrade linux-aws-5.15Upgrade linux-gcp-5.15Upgrade linux-lowlatencyUpgrade linux-azure-5.15Upgrade linux-bluefieldUpgrade linux-oracleUpgrade linux-hwe-5.15Upgrade linux-raspiUpgrade linux-intel-iotgUpgrade linux-kvmUpgrade linux-ibmUpgrade linux-realtimeUpgrade linux-lowlatency-hwe-5.15Upgrade linux-intel-iotg-5.15Upgrade linux-nvidiaUpgrade linux-azureUpgrade linux-oracle-5.15 | Oct 10, 2025 | Oct 4, 2025 |
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