{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2026-23316",
  "modified": "2026-10-07T17:22:01Z",
  "upstream": [
    "CVE-2026-23316"
  ],
  "published": "2026-03-25T10:28:03Z",
  "summary": "net: ipv4: fix ARM64 alignment fault in multipath hash seed",
  "details": "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-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.",
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  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-23316"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/4bdc94d45d5459f0149085dfc1efe733c8e14f11"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/7e4ad34a8889a6a9e0f6cc7c55d02161fe31a199"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/607e923a3c1b2120de430b3dcde25ed8ad213c0a"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/4ee7fa6cf78ff26d783d39e2949d14c4c1cd5e7f"
    }
  ],
  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-05-12T04:54:46Z"
  }
}