CVE-2022-50488 in Linux
Summary
by MITRE • 10/04/2025
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.
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Analysis
by VulDB Data Team • 03/01/2026
The vulnerability described in CVE-2022-50488 represents a use-after-free condition affecting the Block I/O Quality of Service (BFQ) subsystem within the Linux kernel version 5.10. This issue manifests specifically in the handling of block queue structures during process cgroup transitions and demonstrates a classic memory safety flaw that can lead to system instability or potential privilege escalation. The problem occurs when processes are moved between control groups, creating scenarios where multiple block queue structures reference the same block I/O context, leading to improper memory deallocation sequences. The kernel's KASAN (Kernel Address Sanitizer) detected this issue during a filesystem stress test scenario, revealing that the bfq_select_queue function attempted to access memory that had already been freed, resulting in a kernel panic or undefined behavior.
The technical root cause lies in how the BFQ I/O scheduler manages block queue structures when processes transition between cgroups. The fix addresses a race condition that occurs during cgroup migration operations, where the old block queue structure (bfqq) and the new block queue structure can both reference the same block I/O context (bic) during the transition period. When process 2 exits after being moved to a new cgroup, the block I/O context is freed, but the old block queue structure may still hold references to it. This scenario creates a use-after-free condition that violates the fundamental principle of memory safety in kernel space operations. The vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions in software systems. The issue is particularly concerning because it operates at the kernel level where memory corruption can lead to complete system compromise, making it a critical vulnerability for system security.
The operational impact of this vulnerability extends beyond simple system crashes, potentially enabling attackers to exploit the memory corruption for privilege escalation or denial-of-service attacks. The attack surface is particularly relevant for systems running kernel version 5.10 where BFQ I/O scheduling is active, and where multiple processes frequently move between cgroups. The vulnerability's exploitation requires specific conditions involving cgroup transitions and concurrent I/O operations, but once triggered, it can lead to kernel memory corruption that may allow an attacker to execute arbitrary code with kernel privileges. The mitigation strategy involves clearing the bfqq->bic reference during the detachment process, ensuring proper memory ordering and preventing the scenario where freed memory continues to be referenced by stale queue structures. This fix directly addresses the ATT&CK technique T1068, which involves exploiting local privilege escalation vulnerabilities, and demonstrates the critical importance of proper memory management in kernel subsystems. The vulnerability highlights the complexity of managing shared resources in kernel I/O schedulers and underscores the necessity of thorough testing for race conditions in concurrent systems.
The resolution implemented through commit 3bc5e683c67d specifically targets the memory management issue by ensuring that block queue structures properly clear their references to block I/O contexts before the contexts are freed. This approach prevents the use-after-free scenario by breaking the reference chain between the old block queue structure and the block I/O context during cgroup transitions. The fix maintains backward compatibility while addressing the core memory safety issue that could have been exploited in environments with high I/O activity and frequent cgroup operations. Organizations should prioritize applying this kernel patch as it directly addresses a vulnerability that could be leveraged for system compromise. The vulnerability's classification as a kernel memory safety issue places it within the scope of critical security advisories, and its resolution demonstrates the ongoing challenges in maintaining secure kernel implementations. The fix also emphasizes the importance of proper resource management in kernel subsystems, particularly those handling concurrent I/O operations where multiple processes interact with shared scheduling structures.