CVE-2026-23316 (GCVE-0-2026-23316)
Vulnerability from cvelistv5
Published
2026-03-25 10:27
Modified
2026-04-13 06:04
Severity ?
VLAI Severity ?
EPSS score ?
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.
References
| URL | Tags | |
|---|---|---|
Impacted products
{
"containers": {
"cna": {
"affected": [
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"product": "Linux",
"programFiles": [
"include/net/ip_fib.h",
"net/ipv4/sysctl_net_ipv4.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"versions": [
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"versionType": "git"
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]
},
{
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"product": "Linux",
"programFiles": [
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],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
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"version": "6.11"
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{
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"versionType": "semver"
},
{
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"status": "unaffected",
"version": "6.12.77",
"versionType": "semver"
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{
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"status": "unaffected",
"version": "6.18.17",
"versionType": "semver"
},
{
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"status": "unaffected",
"version": "6.19.7",
"versionType": "semver"
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"status": "unaffected",
"version": "7.0",
"versionType": "original_commit_for_fix"
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"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."
}
],
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"dateUpdated": "2026-04-13T06:04:15.316Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
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"references": [
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"url": "https://git.kernel.org/stable/c/4bdc94d45d5459f0149085dfc1efe733c8e14f11"
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{
"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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"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-23316",
"datePublished": "2026-03-25T10:27:11.028Z",
"dateReserved": "2026-01-13T15:37:45.995Z",
"dateUpdated": "2026-04-13T06:04:15.316Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
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}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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