CVE-2022-48994 in Linux
Summary
by MITRE • 10/21/2024
In the Linux kernel, the following vulnerability has been resolved:
ALSA: seq: Fix function prototype mismatch in snd_seq_expand_var_event
With clang's kernel control flow integrity (kCFI, CONFIG_CFI_CLANG), indirect call targets are validated against the expected function pointer prototype to make sure the call target is valid to help mitigate ROP attacks. If they are not identical, there is a failure at run time, which manifests as either a kernel panic or thread getting killed.
seq_copy_in_user() and seq_copy_in_kernel() did not have prototypes matching snd_seq_dump_func_t. Adjust this and remove the casts. There are not resulting binary output differences.
This was found as a result of Clang's new -Wcast-function-type-strict flag, which is more sensitive than the simpler -Wcast-function-type, which only checks for type width mismatches.
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Analysis
by VulDB Data Team • 01/18/2026
The vulnerability identified as CVE-2022-48994 resides within the Linux kernel's Advanced Linux Sound Architecture (ALSA) subsystem, specifically affecting the sequencer component responsible for handling audio event processing. This issue represents a function prototype mismatch that occurs in the snd_seq_expand_var_event function, which is part of the kernel's sound subsystem architecture. The ALSA sequencer component manages complex audio event routing and processing, making it a critical element in the kernel's multimedia capabilities. When the kernel is compiled with Clang's control flow integrity features enabled, particularly CONFIG_CFI_CLANG, this mismatch becomes a critical runtime error that can compromise system stability and security.
The technical flaw manifests through an improper function pointer prototype definition that creates a mismatch between the expected function signature and the actual implementation. Specifically, the seq_copy_in_user() and seq_copy_in_kernel() functions lack the correct prototype matching the snd_seq_dump_func_t type definition. This mismatch occurs because these functions are used in indirect function calls within the sequencer's event processing pipeline, where the kernel's control flow integrity mechanism validates all indirect call targets against their expected prototypes. The vulnerability is particularly dangerous because it operates at the kernel level where incorrect function pointer usage can lead to severe system instability, potentially resulting in kernel panics or thread termination. This type of issue falls under the CWE-688 vulnerability category, which describes improper use of function pointers, and represents a direct threat to kernel integrity and system availability.
The operational impact of this vulnerability extends beyond simple system instability to encompass potential security implications in environments where kernel control flow integrity is enforced. When the kernel operates with Clang's enhanced function pointer validation enabled through the -Wcast-function-type-strict flag, any prototype mismatches trigger runtime failures that can compromise the entire system's audio processing capabilities. The vulnerability affects systems running Linux kernels compiled with specific security hardening options, particularly those utilizing Clang's more stringent function pointer validation mechanisms. Attackers could potentially exploit this weakness to cause denial of service conditions or, in more sophisticated scenarios, to bypass certain control flow integrity protections that are designed to prevent return-oriented programming (ROP) attacks. The vulnerability's classification aligns with ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation', though the immediate impact is more focused on system stability than privilege escalation.
The resolution for CVE-2022-48994 involves correcting the function prototypes to ensure proper alignment with the snd_seq_dump_func_t definition and eliminating the problematic casts that were previously used to work around the prototype mismatch. This fix maintains binary compatibility while ensuring that the kernel's control flow integrity mechanisms operate correctly without false positives or failures. The solution addresses the root cause by ensuring that all function pointers used in the sequencer's event processing pipeline have matching prototypes, thereby preventing the runtime validation failures that would otherwise occur. Security researchers identified this issue through the use of Clang's enhanced warning flags, specifically -Wcast-function-type-strict, which provides more comprehensive validation than the traditional -Wcast-function-type flag. The fix demonstrates proper kernel development practices that emphasize function signature consistency and maintainability, preventing similar issues from arising in the future. This vulnerability represents a classic example of how modern compiler features and security hardening options can reveal latent issues in kernel code that might otherwise remain undetected until specific compilation configurations are used. The resolution ensures that the ALSA sequencer component operates reliably under all supported kernel compilation environments while maintaining the security benefits provided by control flow integrity mechanisms.