CVE-2021-47552: Vulnerability in Linux Linux

Severity: highType: vulnerabilityCVE-2021-47552

In the Linux kernel, the following vulnerability has been resolved: blk-mq: cancel blk-mq dispatch work in both blk_cleanup_queue and disk_release() For avoiding to slow down queue destroy, we don't call blk_mq_quiesce_queue() in blk_cleanup_queue(), instead of delaying to cancel dispatch work in blk_release_queue(). However, this way has caused kernel oops[1], reported by Changhui. The log shows that scsi_device can be freed before running blk_release_queue(), which is expected too since scsi_device is released after the scsi disk is closed and the scsi_device is removed. Fixes the issue by canceling blk-mq dispatch work in both blk_cleanup_queue() and disk_release(): 1) when disk_release() is run, the disk has been closed, and any sync dispatch activities have been done, so canceling dispatch work is enough to quiesce filesystem I/O dispatch activity. 2) in blk_cleanup_queue(), we only focus on passthrough request, and passthrough request is always explicitly allocated & freed by its caller, so once queue is frozen, all sync dispatch activity for passthrough request has been done, then it is enough to just cancel dispatch work for avoiding any dispatch activity. [1] kernel panic log [12622.769416] BUG: kernel NULL pointer dereference, address: 0000000000000300 [12622.777186] #PF: supervisor read access in kernel mode [12622.782918] #PF: error_code(0x0000) - not-present page [12622.788649] PGD 0 P4D 0 [12622.791474] Oops: 0000 [#1] PREEMPT SMP PTI [12622.796138] CPU: 10 PID: 744 Comm: kworker/10:1H Kdump: loaded Not tainted 5.15.0+ #1 [12622.804877] Hardware name: Dell Inc. PowerEdge R730/0H21J3, BIOS 1.5.4 10/002/2015 [12622.813321] Workqueue: kblockd blk_mq_run_work_fn [12622.818572] RIP: 0010:sbitmap_get+0x75/0x190 [12622.823336] Code: 85 80 00 00 00 41 8b 57 08 85 d2 0f 84 b1 00 00 00 45 31 e4 48 63 cd 48 8d 1c 49 48 c1 e3 06 49 03 5f 10 4c 8d 6b 40 83 f0 01 <48> 8b 33 44 89 f2 4c 89 ef 0f b6 c8 e8 fa f3 ff ff 83 f8 ff 75 58 [12622.844290] RSP: 0018:ffffb00a446dbd40 EFLAGS: 00010202 [12622.850120] RAX: 0000000000000001 RBX: 0000000000000300 RCX: 0000000000000004 [12622.858082] RDX: 0000000000000006 RSI: 0000000000000082 RDI: ffffa0b7a2dfe030 [12622.866042] RBP: 0000000000000004 R08: 0000000000000001 R09: ffffa0b742721334 [12622.874003] R10: 0000000000000008 R11: 0000000000000008 R12: 0000000000000000 [12622.881964] R13: 0000000000000340 R14: 0000000000000000 R15: ffffa0b7a2dfe030 [12622.889926] FS: 0000000000000000(0000) GS:ffffa0baafb40000(0000) knlGS:0000000000000000 [12622.898956] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [12622.905367] CR2: 0000000000000300 CR3: 0000000641210001 CR4: 00000000001706e0 [12622.913328] Call Trace: [12622.916055] <TASK> [12622.918394] scsi_mq_get_budget+0x1a/0x110 [12622.922969] __blk_mq_do_dispatch_sched+0x1d4/0x320 [12622.928404] ? pick_next_task_fair+0x39/0x390 [12622.933268] __blk_mq_sched_dispatch_requests+0xf4/0x140 [12622.939194] blk_mq_sched_dispatch_requests+0x30/0x60 [12622.944829] __blk_mq_run_hw_queue+0x30/0xa0 [12622.949593] process_one_work+0x1e8/0x3c0 [12622.954059] worker_thread+0x50/0x3b0 [12622.958144] ? rescuer_thread+0x370/0x370 [12622.962616] kthread+0x158/0x180 [12622.966218] ? set_kthread_struct+0x40/0x40 [12622.970884] ret_from_fork+0x22/0x30 [12622.974875] </TASK> [12622.977309] Modules linked in: scsi_debug rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver nfs lockd grace fscache netfs sunrpc dm_multipath intel_rapl_msr intel_rapl_common dell_wmi_descriptor sb_edac rfkill video x86_pkg_temp_thermal intel_powerclamp dcdbas coretemp kvm_intel kvm mgag200 irqbypass i2c_algo_bit rapl drm_kms_helper ipmi_ssif intel_cstate intel_uncore syscopyarea sysfillrect sysimgblt fb_sys_fops pcspkr cec mei_me lpc_ich mei ipmi_si ipmi_devintf ipmi_msghandler acpi_power_meter drm fuse xfs libcrc32c sr_mod cdrom sd_mod t10_pi sg ixgbe ahci libahci crct10dif_pclmul crc32_pclmul crc32c_intel libata megaraid_sas ghash_clmulni_intel tg3 wdat_w ---truncated---

AI Analysis

Technical Summary

CVE-2021-47552 is a vulnerability identified in the Linux kernel's block multi-queue (blk-mq) subsystem, which is responsible for managing I/O request dispatching to storage devices. The issue arises from improper cancellation of blk-mq dispatch work during queue cleanup and disk release operations. Specifically, the original implementation avoided calling blk_mq_quiesce_queue() in blk_cleanup_queue() to prevent slowing down queue destruction, opting instead to delay cancellation of dispatch work until blk_release_queue(). However, this approach led to a kernel oops (a type of kernel panic) due to a NULL pointer dereference. The root cause is that the scsi_device structure can be freed before blk_release_queue() runs, causing the blk-mq dispatch work to access invalid memory. The fix involves canceling blk-mq dispatch work in both blk_cleanup_queue() and disk_release(), ensuring that all dispatch activities are properly quiesced and preventing use-after-free conditions. The vulnerability can lead to kernel panics and system instability, as demonstrated by the detailed kernel panic logs included in the description. The issue affects Linux kernel versions prior to the patch and is particularly relevant for systems using SCSI devices and blk-mq for I/O scheduling. No known exploits are reported in the wild, and no CVSS score has been assigned yet.

Potential Impact

For European organizations, this vulnerability poses a risk primarily to servers and infrastructure running vulnerable Linux kernel versions with blk-mq enabled, especially those handling critical storage I/O operations. The impact includes potential denial of service (DoS) through kernel panics, leading to system crashes and downtime. This can disrupt business operations, data processing, and availability of services relying on affected Linux systems. Since the vulnerability can cause kernel oops and crashes without requiring user interaction or authentication, it may be triggered by normal I/O workloads or specific storage operations, increasing the risk of unintentional outages. Organizations with high-availability requirements, such as financial institutions, healthcare providers, and cloud service providers in Europe, could experience significant operational impact. While no direct data breach or privilege escalation is indicated, the loss of availability and potential data corruption risks necessitate prompt mitigation.

Mitigation Recommendations

European organizations should prioritize updating their Linux kernel to the fixed versions that include the patch for CVE-2021-47552. Kernel updates should be tested in staging environments to ensure compatibility with existing workloads. Additionally, organizations should audit their systems to identify those running vulnerable kernel versions, particularly focusing on servers with heavy SCSI and blk-mq usage. Implementing robust monitoring for kernel oops and system crashes can help detect exploitation attempts or instability early. Where immediate patching is not feasible, temporarily disabling blk-mq or adjusting I/O scheduler settings to avoid triggering the vulnerable code paths may reduce risk, although this could impact performance. Organizations should also ensure regular backups and disaster recovery plans are in place to mitigate potential data loss from unexpected crashes. Collaboration with Linux distribution vendors for timely patch deployment and security advisories is recommended.