CVE-2026-74643 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
samples/damon/mtier: error out for zero quota goal target values
Patch series "mm/damon: avoid division by zero from damos_quota_score()".
DAMON_SAMPLE_MTIER and DAMON_LRU_SORT allow the user to trigger division by zero in damos_quota_score(). Avoid it by adding parameters validation checks.
This patch (of 2):
damos_quota_score() can trigger division by zero if the target_value is zero. DAMON_SAMPLE_MTIER lets users set the target_value via node0_mem_{used,free}_bp parameters. It doesn't guard zero value case,
though. As a result, users can trigger division by zero. Fix the issue by returning an error when the user tries to start DAMON with zero node0_mem_{used,free}_bp parameter values.
DAMON_SAMPLE_MTIER is just a sample module, but the consequence is quite bad. Also the zero node0_mem_free_bp parameter might look like a reasonable setup to some users. Hence, the issue might really happen in the real world.
One reliable way to reproduce the issue is like below:
# cd /sys/module/damon_sample_mtier/parameters # echo 4096 > node0_start_addr # echo 8192 > node0_end_addr # echo 8192 > node1_start_addr # echo 81920 > node1_end_addr # echo 0 > node0_mem_free_bp # echo Y > enabled # dmesg -w [...]
[18792.235916] Oops: divide error: 0000 [#1] SMP NOPTI
[...]
[18792.242787] RIP: 0010:damos_quota_score+0x6f/0x480
[...]
This issue was discovered [1] by Sashiko.
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Analysis
by VulDB Data Team • 08/22/2026
The Linux kernel vulnerability identified in the DAMON sample modules, specifically damon_sample_mtier and damon_lru_sort, represents a critical input validation failure that leads to a division-by-zero error within the damos_quota_score function. This flaw arises because these experimental memory access pattern monitoring components allow userspace applications to configure target values for quota goals through sysfs parameters such as node0_mem_used_bp and node0_mem_free_bp. The underlying implementation of damos_quota_score performs arithmetic operations that assume non-zero divisor inputs, yet it lacks the necessary defensive programming checks to validate user-supplied data before execution. Consequently, when a user sets one of these target value parameters to zero and enables the DAMON sample module, the kernel attempts to divide by this zero value during quota scoring calculations. This mathematical impossibility triggers an invalid opcode exception in the kernel space, manifesting as a division error oops that can crash the affected system or destabilize the operating environment depending on the context of execution and available fault handling mechanisms.
From a technical perspective, this vulnerability is classified under CWE-369, which denotes Divide By Zero errors, specifically occurring due to insufficient validation of user-controlled input data before its use in arithmetic operations. The attack vector involves local interaction with the sysfs interface, requiring an attacker or misconfigured administrator to write specific zero values into the module parameters and subsequently enable the monitoring service. Although DAMON_SAMPLE_MTIER is categorized as a sample module intended for development and testing purposes rather than production deployment, it remains compiled into many kernel configurations by default due to its utility in demonstrating advanced memory management features. The presence of this code path means that any system running these kernels with the associated modules enabled is potentially susceptible if an attacker gains write access to the relevant sysfs entries or exploits a local privilege escalation vulnerability to gain such access.
The operational impact of this flaw extends beyond simple service disruption within the sample module itself. A kernel-level division-by-zero error typically results in a panic or oops, which can lead to system instability, data corruption if ongoing operations are interrupted abruptly, or a complete denial of service through system reboot. In environments where DAMON is used for performance tuning and memory optimization, such crashes could disrupt critical workloads that rely on continuous monitoring and adaptive behavior adjustments based on quota scores. Furthermore, the potential for this issue to occur in real-world scenarios is heightened by the fact that zero values might appear as reasonable default or edge-case configurations to users unfamiliar with the internal arithmetic constraints of the damos_quota_score function. This increases the likelihood of accidental triggering rather than solely malicious exploitation.
Mitigation strategies primarily involve applying the upstream kernel patch series that introduces explicit parameter validation checks within the damon_sample_mtier and damon_lru_sort modules. These patches ensure that any attempt to set node0_mem_used_bp or node0_mem_free_bp to zero results in an immediate error return rather than proceeding with invalid configuration states. Administrators should verify their current kernel versions against vendor security advisories and apply updates as soon as they become available. In the interim, if patching is not immediately feasible, disabling these specific sample modules by unloading them or preventing their loading via module blacklisting can effectively neutralize the attack vector. Additionally, restricting write access to /sys/module/damon_sample_mtier/parameters through strict filesystem permissions and SELinux policies adds a layer of defense-in-depth, ensuring that only authorized processes with appropriate privileges can modify these sensitive kernel parameters.
This incident highlights the importance of rigorous input validation even in sample or experimental code paths within the Linux kernel. While such modules are not intended for production use, their inclusion in default builds exposes them to potential abuse by local users who may have gained unauthorized access through other vulnerabilities. The fix aligns with best practices for secure coding in operating system kernels, emphasizing that all user-supplied data must be validated against expected ranges and constraints before being used in critical arithmetic or logical operations. By addressing this flaw, the Linux kernel community reinforces the robustness of its memory management subsystems and reduces the attack surface available to local attackers seeking to cause denial-of-service conditions through simple parameter manipulation.