CVE-2022-48740 in Linux
Summary
by MITRE • 06/20/2024
In the Linux kernel, the following vulnerability has been resolved:
selinux: fix double free of cond_list on error paths
On error path from cond_read_list() and duplicate_policydb_cond_list() the cond_list_destroy() gets called a second time in caller functions, resulting in NULL pointer deref. Fix this by resetting the cond_list_len to 0 in cond_list_destroy(), making subsequent calls a noop.
Also consistently reset the cond_list pointer to NULL after freeing.
[PM: fix line lengths in the description]
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Analysis
by VulDB Data Team • 06/19/2025
The vulnerability identified as CVE-2022-48740 represents a critical double free condition within the Linux kernel's Security-Enhanced Linux (SELinux) implementation that can lead to system instability and potential privilege escalation. This flaw exists in the conditional policy list handling mechanism where the kernel's security subsystem manages conditional access control rules. The vulnerability specifically affects the selinux subsystem's ability to properly manage memory resources during error conditions in conditional policy list operations. The issue manifests when the kernel encounters errors during the processing of conditional policy lists, particularly during the cond_read_list() and duplicate_policydb_cond_list() functions where the cond_list_destroy() cleanup routine is invoked multiple times.
The technical root cause of this vulnerability lies in improper memory management within the SELinux subsystem's conditional policy handling code. When error conditions occur during the processing of conditional policy lists, the system attempts to destroy the cond_list structure twice, leading to a double free scenario. The first call to cond_list_destroy() properly frees the memory, but subsequent calls attempt to free already released memory locations, resulting in a NULL pointer dereference. This memory management error stems from the lack of proper state tracking within the cond_list_destroy() function, which fails to prevent re-entrancy during cleanup operations. The vulnerability is classified under CWE-415 as Double Free, which represents a well-known memory corruption vulnerability that can be exploited to execute arbitrary code or cause system crashes.
The operational impact of CVE-2022-48740 extends beyond simple system crashes to potentially enable privilege escalation and denial of service attacks. An attacker who can trigger the specific error conditions leading to this double free scenario could potentially cause the kernel to crash or, in more sophisticated exploitation attempts, manipulate the memory layout to execute arbitrary code with kernel privileges. This vulnerability affects all Linux systems running kernel versions that include the affected SELinux implementation, making it particularly concerning for enterprise environments where SELinux is actively deployed. The vulnerability aligns with ATT&CK technique T1068 by enabling local privilege escalation through kernel memory corruption, and T1499 by potentially causing system instability and denial of service conditions.
The fix implemented for this vulnerability involves modifying the cond_list_destroy() function to reset the cond_list_len variable to zero upon destruction, effectively making subsequent calls to the function no-ops. Additionally, the implementation consistently resets the cond_list pointer to NULL after freeing the memory, preventing any further access to the freed memory location. This approach follows the standard practice of implementing idempotent cleanup functions that can be safely called multiple times without causing memory corruption. The solution addresses the root cause by ensuring that the memory management state is properly maintained throughout the cleanup process, preventing the double free condition from occurring. The mitigation strategy also aligns with the principle of defensive programming by ensuring that all pointers are properly nullified after deallocation, which helps prevent use-after-free vulnerabilities that could be exploited by malicious actors. Organizations should apply the relevant kernel updates containing this fix as soon as possible to protect their systems from potential exploitation of this memory corruption vulnerability.