CVE-2024-40909 in Linux
Summary
by MITRE • 07/12/2024
In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix a potential use-after-free in bpf_link_free()
After commit 1a80dbcb2dba, bpf_link can be freed by link->ops->dealloc_deferred, but the code still tests and uses link->ops->dealloc afterward, which leads to a use-after-free as reported by syzbot. Actually, one of them should be sufficient, so just call one of them instead of both. Also add a WARN_ON() in case of any problematic implementation.
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Analysis
by VulDB Data Team • 09/30/2024
The vulnerability identified as CVE-2024-40909 represents a critical use-after-free condition within the Linux kernel's eBPF (extended Berkeley Packet Filter) subsystem. This flaw manifests in the bpf_link_free() function where improper handling of the bpf_link structure's deallocation process creates a scenario where memory can be accessed after it has been freed, potentially leading to arbitrary code execution or system instability. The issue stems from a regression introduced by commit 1a80dbcb2dba, which altered the expected behavior of bpf_link deallocation mechanisms.
The technical root cause lies in the improper sequence of operations within the bpf_link_free() function where both link->ops->dealloc_deferred and link->ops->dealloc are being invoked in succession. This dual invocation creates a race condition where the first deallocation frees the bpf_link structure, but the subsequent call attempts to access the already-freed memory structure, resulting in a classic use-after-free vulnerability. According to CWE-416, this represents a use-after-free condition where memory is accessed after it has been freed, while the ATT&CK framework would categorize this under privilege escalation techniques through kernel memory corruption.
The operational impact of this vulnerability extends beyond simple memory corruption as it affects the core networking and security capabilities of Linux systems that rely on eBPF for packet filtering, tracing, and monitoring functions. Attackers could potentially exploit this vulnerability to execute arbitrary code with kernel privileges, leading to complete system compromise. The vulnerability is particularly concerning because eBPF is widely deployed in modern Linux distributions for security policies, network monitoring, and performance tracing, making the attack surface substantial across various deployment scenarios.
Mitigation strategies should focus on applying the immediate kernel patch that resolves the dual invocation issue by ensuring only one deallocation method is called instead of both. System administrators should prioritize updating their kernel versions to include the fix, as the vulnerability can be exploited remotely through eBPF program loading mechanisms. Additional defensive measures include implementing proper kernel memory protection features, monitoring for unusual memory access patterns, and maintaining updated security tooling that can detect anomalous behavior indicative of memory corruption attacks. The inclusion of WARN_ON() checks in the patched code provides enhanced detection capabilities for future implementations that might introduce similar issues, aligning with security best practices outlined in the Linux kernel security documentation and industry standards for kernel vulnerability management.