CVE-2026-23316 (GCVE-0-2026-23316)

Vulnerability from cvelistv5 – Published: 2026-03-25 10:27 – Updated: 2026-03-25 10:27
VLAI?
Title
net: ipv4: fix ARM64 alignment fault in multipath hash seed
Summary
In the Linux kernel, the following vulnerability has been resolved: net: ipv4: fix ARM64 alignment fault in multipath hash seed `struct sysctl_fib_multipath_hash_seed` contains two u32 fields (user_seed and mp_seed), making it an 8-byte structure with a 4-byte alignment requirement. In `fib_multipath_hash_from_keys()`, the code evaluates the entire struct 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 regular loads which the ARM64 kernel tolerates, it causes a fatal kernel panic when compiled with Clang and LTO enabled. Commit e35123d83ee3 ("arm64: lto: Strengthen READ_ONCE() to acquire when CONFIG_LTO=y") strengthens `READ_ONCE()` to use Load-Acquire instructions (`ldar` / `ldapr`) to prevent compiler reordering bugs under Clang LTO. Since the macro evaluates the full 8-byte struct, Clang emits a 64-bit `ldar` instruction. ARM64 architecture strictly requires `ldar` to be naturally aligned, thus executing it on a 4-byte aligned address triggers a strict Alignment Fault (FSC = 0x21). Fix the read side by moving the `READ_ONCE()` directly to the `u32` member, which emits a safe 32-bit `ldar Wn`. Furthermore, Eric Dumazet pointed out that `WRITE_ONCE()` on the entire struct in `proc_fib_multipath_hash_set_seed()` is also flawed. Analysis shows that Clang splits this 8-byte write into two separate 32-bit `str` instructions. While this avoids an alignment fault, it destroys atomicity and exposes a tear-write vulnerability. Fix this by explicitly splitting the write into two 32-bit `WRITE_ONCE()` operations. Finally, add the missing `READ_ONCE()` when reading `user_seed` in `proc_fib_multipath_hash_seed()` to ensure proper pairing and concurrency safety.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 , < 4bdc94d45d5459f0149085dfc1efe733c8e14f11 (git)
Affected: 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 , < 7e4ad34a8889a6a9e0f6cc7c55d02161fe31a199 (git)
Affected: 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 , < 607e923a3c1b2120de430b3dcde25ed8ad213c0a (git)
Affected: 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 , < 4ee7fa6cf78ff26d783d39e2949d14c4c1cd5e7f (git)
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    Linux Linux Affected: 6.11
Unaffected: 0 , < 6.11 (semver)
Unaffected: 6.12.77 , ≤ 6.12.* (semver)
Unaffected: 6.18.17 , ≤ 6.18.* (semver)
Unaffected: 6.19.7 , ≤ 6.19.* (semver)
Unaffected: 7.0-rc3 , ≤ * (original_commit_for_fix)
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          "product": "Linux",
          "programFiles": [
            "include/net/ip_fib.h",
            "net/ipv4/sysctl_net_ipv4.c"
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          "vendor": "Linux",
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          "lang": "en",
          "value": "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-\u003eipv4.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."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-03-25T10:27:11.028Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "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"
        }
      ],
      "title": "net: ipv4: fix ARM64 alignment fault in multipath hash seed",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-23316",
    "datePublished": "2026-03-25T10:27:11.028Z",
    "dateReserved": "2026-01-13T15:37:45.995Z",
    "dateUpdated": "2026-03-25T10:27:11.028Z",
    "state": "PUBLISHED"
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    "nvd": "{\"cve\":{\"id\":\"CVE-2026-23316\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-03-25T11:16:28.063\",\"lastModified\":\"2026-03-25T15:41:33.977\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"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-\u003eipv4.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.\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/4bdc94d45d5459f0149085dfc1efe733c8e14f11\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/4ee7fa6cf78ff26d783d39e2949d14c4c1cd5e7f\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/607e923a3c1b2120de430b3dcde25ed8ad213c0a\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/7e4ad34a8889a6a9e0f6cc7c55d02161fe31a199\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
  }
}


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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
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