{"id":"CVE-2026-23316","title":"net: ipv4: fix ARM64 alignment fault in multipath hash seed","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv4: fix ARM64 alignment fault in multipath hash seed\n\n`struct sysctl_fib_multipath_hash_seed` contains two u32 fields\n(user_seed and mp_seed), making it an 8-byt…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 < 4bdc94d45d5459f0149085dfc1efe733c8e14f11","Linux >= 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 < 7e4ad34a8889a6a9e0f6cc7c55d02161fe31a199","Linux >= 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 < 607e923a3c1b2120de430b3dcde25ed8ad213c0a","Linux >= 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 < 4ee7fa6cf78ff26d783d39e2949d14c4c1cd5e7f","Linux 6.11"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"partial","timestamp":"2026-11-05T21:26:49.330326Z"},"published":"2026-03-25","updated":"2026-11-05","sourceUpdated":"2026-11-05T21:33:38.599Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-23316","references":[{"url":"https://git.kernel.org/stable/c/4bdc94d45d5459f0149085dfc1efe733c8e14f11"},{"url":"https://git.kernel.org/stable/c/7e4ad34a8889a6a9e0f6cc7c55d02161fe31a199"},{"url":"https://git.kernel.org/stable/c/607e923a3c1b2120de430b3dcde25ed8ad213c0a"},{"url":"https://git.kernel.org/stable/c/4ee7fa6cf78ff26d783d39e2949d14c4c1cd5e7f"}],"tags":["cve.org"],"epss":0.00127,"epssPercentile":0.02368,"ingestedAt":"2026-11-05T22:38:32.117Z","slug":"CVE-2026-23316","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv4: fix ARM64 alignment fault in multipath hash seed\n\n`struct sysctl_fib_multipath_hash_seed` contains two u32 fields\n(user_seed and mp_seed), making it an 8-byte structure with a 4-byte\nalignment requirement.\n\nIn `fib_multipath_hash_from_keys()`, the code evaluates the entire\nstruct atomically via `READ_ONCE()`:\n\n    mp_seed = READ_ONCE(net->ipv4.sysctl_fib_multipath_hash_seed).mp_seed;\n\nWhile this silently works on GCC by falling back to unaligned regular\nloads which the ARM64 kernel tolerates, it causes a fatal kernel panic\nwhen compiled with Clang and LTO enabled.\n\nCommit e35123d83ee3 (\"arm64: lto: Strengthen READ_ONCE() to acquire\nwhen CONFIG_LTO=y\") strengthens `READ_ONCE()` to use Load-Acquire\ninstructions (`ldar` / `ldapr`) to prevent compiler reordering bugs\nunder Clang LTO. Since the macro evaluates the full 8-byte struct,\nClang emits a 64-bit `ldar` instruction. ARM64 architecture strictly\nrequires `ldar` to be naturally aligned, thus executing it on a 4-byte\naligned address triggers a strict Alignment Fault (FSC = 0x21).\n\nFix the read side by moving the `READ_ONCE()` directly to the `u32`\nmember, which emits a safe 32-bit `ldar Wn`.\n\nFurthermore, Eric Dumazet pointed out that `WRITE_ONCE()` on the entire\nstruct in `proc_fib_multipath_hash_set_seed()` is also flawed. Analysis\nshows that Clang splits this 8-byte write into two separate 32-bit\n`str` instructions. While this avoids an alignment fault, it destroys\natomicity and exposes a tear-write vulnerability. Fix this by\nexplicitly splitting the write into two 32-bit `WRITE_ONCE()`\noperations.\n\nFinally, add the missing `READ_ONCE()` when reading `user_seed` in\n`proc_fib_multipath_hash_seed()` to ensure proper pairing and\nconcurrency safety.\n\n## Affected\n\n- `Linux >= 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 < 4bdc94d45d5459f0149085dfc1efe733c8e14f11`\n- `Linux >= 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 < 7e4ad34a8889a6a9e0f6cc7c55d02161fe31a199`\n- `Linux >= 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 < 607e923a3c1b2120de430b3dcde25ed8ad213c0a`\n- `Linux >= 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 < 4ee7fa6cf78ff26d783d39e2949d14c4c1cd5e7f`\n- `Linux 6.11`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}