CVE-2023-54242
Description
In the Linux kernel, the following vulnerability has been resolved:
block, bfq: Fix division by zero error on zero wsum
When the weighted sum is zero the calculation of limit causes a division by zero error. Fix this by continuing to the next level.
This was discovered by running as root:
stress-ng --ioprio 0
Fixes divison by error oops:
[ 521.450556] divide error: 0000 [#1] SMP NOPTI [ 521.450766] CPU: 2 PID: 2684464 Comm: stress-ng-iopri Not tainted 6.2.1-1280.native #1 [ 521.451117] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.1-0-g3208b098f51a-prebuilt.qemu.org 04/01/2014 [ 521.451627] RIP: 0010:bfqq_request_over_limit+0x207/0x400 [ 521.451875] Code: 01 48 8d 0c c8 74 0b 48 8b 82 98 00 00 00 48 8d 0c c8 8b 85 34 ff ff ff 48 89 ca 41 0f af 41 50 48 d1 ea 48 98 48 01 d0 31 d2 <48> f7 f1 41 39 41 48 89 85 34 ff ff ff 0f 8c 7b 01 00 00 49 8b 44 [ 521.452699] RSP: 0018:ffffb1af84eb3948 EFLAGS: 00010046 [ 521.452938] RAX: 000000000000003c RBX: 0000000000000000 RCX: 0000000000000000 [ 521.453262] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffb1af84eb3978 [ 521.453584] RBP: ffffb1af84eb3a30 R08: 0000000000000001 R09: ffff8f88ab8a4ba0 [ 521.453905] R10: 0000000000000000 R11: 0000000000000001 R12: ffff8f88ab8a4b18 [ 521.454224] R13: ffff8f8699093000 R14: 0000000000000001 R15: ffffb1af84eb3970 [ 521.454549] FS: 00005640b6b0b580(0000) GS:ffff8f88b3880000(0000) knlGS:0000000000000000 [ 521.454912] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 521.455170] CR2: 00007ffcbcae4e38 CR3: 00000002e46de001 CR4: 0000000000770ee0 [ 521.455491] PKRU: 55555554 [ 521.455619] Call Trace: [ 521.455736] [ 521.455837] ? bfq_request_merge+0x3a/0xc0 [ 521.456027] ? elv_merge+0x115/0x140 [ 521.456191] bfq_limit_depth+0xc8/0x240 [ 521.456366] __blk_mq_alloc_requests+0x21a/0x2c0 [ 521.456577] blk_mq_submit_bio+0x23c/0x6c0 [ 521.456766] __submit_bio+0xb8/0x140 [ 521.457236] submit_bio_noacct_nocheck+0x212/0x300 [ 521.457748] submit_bio_noacct+0x1a6/0x580 [ 521.458220] submit_bio+0x43/0x80 [ 521.458660] ext4_io_submit+0x23/0x80 [ 521.459116] ext4_do_writepages+0x40a/0xd00 [ 521.459596] ext4_writepages+0x65/0x100 [ 521.460050] do_writepages+0xb7/0x1c0 [ 521.460492] __filemap_fdatawrite_range+0xa6/0x100 [ 521.460979] file_write_and_wait_range+0xbf/0x140 [ 521.461452] ext4_sync_file+0x105/0x340 [ 521.461882] __x64_sys_fsync+0x67/0x100 [ 521.462305] ? syscall_exit_to_user_mode+0x2c/0x1c0 [ 521.462768] do_syscall_64+0x3b/0xc0 [ 521.463165] entry_SYSCALL_64_after_hwframe+0x5a/0xc4 [ 521.463621] RIP: 0033:0x5640b6c56590 [ 521.464006] Code: 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 80 3d 71 70 0e 00 00 74 17 b8 4a 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 48 c3 0f 1f 80 00 00 00 00 48 83 ec 18 89 7c
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
CVE-2023-54242 is a Linux kernel bug in the BFQ I/O scheduler where a divide-by-zero occurs when the weighted sum (wsum) is zero, causing a system crash.
Root
Cause
In the Linux kernel's Budget Fair Queueing (BFQ) I/O scheduler, the function bfqq_request_over_limit performs a calculation that divides by the weighted sum (wsum). When this sum is zero—a scenario that can be triggered by certain I/O priority settings—the division by zero causes a kernel oops and system instability. The vulnerability was discovered using the stress-ng --ioprio 0 command run as root [1].
Exploitation
The bug exists in the kernel's block layer and can be triggered by a local, unprivileged user (or root) who can set I/O priorities via the ioprio_set system call. An attacker with local access can craft a specific I/O priority pattern that results in a zero weighted sum, leading to the division by zero. No additional authentication is required beyond local access, and the attacker does not need special privileges beyond being able to invoke the relevant system calls.
Impact
If exploited, the vulnerability causes a kernel panic (divide error oops), effectively crashing the system. This constitutes a denial of service (DoS) condition, as the system becomes unavailable. The crash trace shows the fault occurs in bfqq_request_over_limit and propagates up through the I/O request path, ultimately crashing the kernel [1].
Mitigation
The fix has been applied upstream in the Linux kernel via commit 1655cfc85250 ("block, bfq: Fix division by zero error on zero wsum"). This fix checks for a zero weighted sum and continues to the next level instead of performing the division. Users should update their kernel to a version containing this commit to eliminate the vulnerability. No workaround is available for unpatched systems; the only effective mitigation is to apply the kernel patch.
AI Insight generated on May 19, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.
Affected products
1- Range: <=6.2.1-1280
Patches
31655cfc85250c0346a59d719e53413f8deedVulnerability mechanics
Generated on May 9, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.
References
3News mentions
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