CVE-2026-23316

Description

In the Linux kernel, the following vulnerability has been resolved:net: ipv4: fix ARM64 alignment fault in multipath hash seedstruct sysctl_fib_multipath_hash_seed contains two u32 fields(user_seed and mp_seed), making it an 8-byte structure with a 4-bytealignment requirement.In fib_multipath_hash_from_keys(), the code evaluates the entirestruct atomically via READ_ONCE(): mp_seed = READ_ONCE(net->ipv4.sysctl_fib_multipath_hash_seed).mp_seed;While this silently works on GCC by falling back to unaligned regularloads which the ARM64 kernel tolerates, it causes a fatal kernel panicwhen compiled with Clang and LTO enabled.Commit e35123d83ee3 (arm64: lto: Strengthen READ_ONCE() to acquirewhen CONFIG_LTO=y) strengthens READ_ONCE() to use Load-Acquireinstructions (ldar / ldapr) to prevent compiler reordering bugsunder Clang LTO. Since the macro evaluates the full 8-byte struct,Clang emits a 64-bit ldar instruction. ARM64 architecture strictlyrequires ldar to be naturally aligned, thus executing it on a 4-bytealigned address triggers a strict Alignment Fault (FSC = 0x21).Fix the read side by moving the READ_ONCE() directly to the u32member, which emits a safe 32-bit ldar Wn.Furthermore, Eric Dumazet pointed out that WRITE_ONCE() on the entirestruct in proc_fib_multipath_hash_set_seed() is also flawed. Analysisshows that Clang splits this 8-byte write into two separate 32-bitstr instructions. While this avoids an alignment fault, it destroysatomicity and exposes a tear-write vulnerability. Fix this byexplicitly splitting the write into two 32-bit WRITE_ONCE()operations.Finally, add the missing READ_ONCE() when reading user_seed inproc_fib_multipath_hash_seed() to ensure proper pairing andconcurrency safety.

Risk Information

Associated Vulnerability

Patch Details

References

https://nvd.nist.gov/vuln/detail/CVE-2023-1234
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-1234