CVE-2026-43244 (GCVE-0-2026-43244)
Vulnerability from cvelistv5 – Published: 2026-05-06 11:28 – Updated: 2026-05-06 11:28
VLAI?
Title
kcm: fix zero-frag skb in frag_list on partial sendmsg error
Summary
In the Linux kernel, the following vulnerability has been resolved:
kcm: fix zero-frag skb in frag_list on partial sendmsg error
Syzkaller reported a warning in kcm_write_msgs() when processing a
message with a zero-fragment skb in the frag_list.
When kcm_sendmsg() fills MAX_SKB_FRAGS fragments in the current skb,
it allocates a new skb (tskb) and links it into the frag_list before
copying data. If the copy subsequently fails (e.g. -EFAULT from
user memory), tskb remains in the frag_list with zero fragments:
head skb (msg being assembled, NOT yet in sk_write_queue)
+-----------+
| frags[17] | (MAX_SKB_FRAGS, all filled with data)
| frag_list-+--> tskb
+-----------+ +----------+
| frags[0] | (empty! copy failed before filling)
+----------+
For SOCK_SEQPACKET with partial data already copied, the error path
saves this message via partial_message for later completion. For
SOCK_SEQPACKET, sock_write_iter() automatically sets MSG_EOR, so a
subsequent zero-length write(fd, NULL, 0) completes the message and
queues it to sk_write_queue. kcm_write_msgs() then walks the
frag_list and hits:
WARN_ON(!skb_shinfo(skb)->nr_frags)
TCP has a similar pattern where skbs are enqueued before data copy
and cleaned up on failure via tcp_remove_empty_skb(). KCM was
missing the equivalent cleanup.
Fix this by tracking the predecessor skb (frag_prev) when allocating
a new frag_list entry. On error, if the tail skb has zero frags,
use frag_prev to unlink and free it in O(1) without walking the
singly-linked frag_list. frag_prev is safe to dereference because
the entire message chain is only held locally (or in kcm->seq_skb)
and is not added to sk_write_queue until MSG_EOR, so the send path
cannot free it underneath us.
Also change the WARN_ON to WARN_ON_ONCE to avoid flooding the log
if the condition is somehow hit repeatedly.
There are currently no KCM selftests in the kernel tree; a simple
reproducer is available at [1].
[1] https://gist.github.com/mrpre/a94d431c757e8d6f168f4dd1a3749daa
Severity ?
No CVSS data available.
Assigner
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Affected:
ab7ac4eb9832e32a09f4e8042705484d2fb0aad3 , < 9ea3671d70ee07480d80bebe86696397c4e99fb7
(git)
Affected: ab7ac4eb9832e32a09f4e8042705484d2fb0aad3 , < b1e3edf688a88c1a3ac41657055d9c136a08cd25 (git) Affected: ab7ac4eb9832e32a09f4e8042705484d2fb0aad3 , < 7af58f76e4b404a74c836881a845e6652db8a09f (git) Affected: ab7ac4eb9832e32a09f4e8042705484d2fb0aad3 , < ca220141fa8ebae09765a242076b2b77338106b0 (git) |
||
{
"containers": {
"cna": {
"affected": [
{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"net/kcm/kcmsock.c"
],
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"vendor": "Linux",
"versions": [
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{
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"status": "affected",
"version": "ab7ac4eb9832e32a09f4e8042705484d2fb0aad3",
"versionType": "git"
},
{
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"status": "affected",
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"versionType": "git"
}
]
},
{
"defaultStatus": "affected",
"product": "Linux",
"programFiles": [
"net/kcm/kcmsock.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "4.6"
},
{
"lessThan": "4.6",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"version": "6.12.75",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.18.*",
"status": "unaffected",
"version": "6.18.16",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.19.*",
"status": "unaffected",
"version": "6.19.6",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.0",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
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"cpeMatch": [
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.12.75",
"versionStartIncluding": "4.6",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.19.6",
"versionStartIncluding": "4.6",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "7.0",
"versionStartIncluding": "4.6",
"vulnerable": true
}
],
"negate": false,
"operator": "OR"
}
]
}
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"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nkcm: fix zero-frag skb in frag_list on partial sendmsg error\n\nSyzkaller reported a warning in kcm_write_msgs() when processing a\nmessage with a zero-fragment skb in the frag_list.\n\nWhen kcm_sendmsg() fills MAX_SKB_FRAGS fragments in the current skb,\nit allocates a new skb (tskb) and links it into the frag_list before\ncopying data. If the copy subsequently fails (e.g. -EFAULT from\nuser memory), tskb remains in the frag_list with zero fragments:\n\n head skb (msg being assembled, NOT yet in sk_write_queue)\n +-----------+\n | frags[17] | (MAX_SKB_FRAGS, all filled with data)\n | frag_list-+--\u003e tskb\n +-----------+ +----------+\n | frags[0] | (empty! copy failed before filling)\n +----------+\n\nFor SOCK_SEQPACKET with partial data already copied, the error path\nsaves this message via partial_message for later completion. For\nSOCK_SEQPACKET, sock_write_iter() automatically sets MSG_EOR, so a\nsubsequent zero-length write(fd, NULL, 0) completes the message and\nqueues it to sk_write_queue. kcm_write_msgs() then walks the\nfrag_list and hits:\n\n WARN_ON(!skb_shinfo(skb)-\u003enr_frags)\n\nTCP has a similar pattern where skbs are enqueued before data copy\nand cleaned up on failure via tcp_remove_empty_skb(). KCM was\nmissing the equivalent cleanup.\n\nFix this by tracking the predecessor skb (frag_prev) when allocating\na new frag_list entry. On error, if the tail skb has zero frags,\nuse frag_prev to unlink and free it in O(1) without walking the\nsingly-linked frag_list. frag_prev is safe to dereference because\nthe entire message chain is only held locally (or in kcm-\u003eseq_skb)\nand is not added to sk_write_queue until MSG_EOR, so the send path\ncannot free it underneath us.\n\nAlso change the WARN_ON to WARN_ON_ONCE to avoid flooding the log\nif the condition is somehow hit repeatedly.\n\nThere are currently no KCM selftests in the kernel tree; a simple\nreproducer is available at [1].\n\n[1] https://gist.github.com/mrpre/a94d431c757e8d6f168f4dd1a3749daa"
}
],
"providerMetadata": {
"dateUpdated": "2026-05-06T11:28:36.946Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/9ea3671d70ee07480d80bebe86696397c4e99fb7"
},
{
"url": "https://git.kernel.org/stable/c/b1e3edf688a88c1a3ac41657055d9c136a08cd25"
},
{
"url": "https://git.kernel.org/stable/c/7af58f76e4b404a74c836881a845e6652db8a09f"
},
{
"url": "https://git.kernel.org/stable/c/ca220141fa8ebae09765a242076b2b77338106b0"
}
],
"title": "kcm: fix zero-frag skb in frag_list on partial sendmsg error",
"x_generator": {
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}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-43244",
"datePublished": "2026-05-06T11:28:36.946Z",
"dateReserved": "2026-05-01T14:12:55.995Z",
"dateUpdated": "2026-05-06T11:28:36.946Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"vulnerability-lookup:meta": {
"nvd": "{\"cve\":{\"id\":\"CVE-2026-43244\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-05-06T12:16:44.873\",\"lastModified\":\"2026-05-06T13:07:51.607\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nkcm: fix zero-frag skb in frag_list on partial sendmsg error\\n\\nSyzkaller reported a warning in kcm_write_msgs() when processing a\\nmessage with a zero-fragment skb in the frag_list.\\n\\nWhen kcm_sendmsg() fills MAX_SKB_FRAGS fragments in the current skb,\\nit allocates a new skb (tskb) and links it into the frag_list before\\ncopying data. If the copy subsequently fails (e.g. -EFAULT from\\nuser memory), tskb remains in the frag_list with zero fragments:\\n\\n head skb (msg being assembled, NOT yet in sk_write_queue)\\n +-----------+\\n | frags[17] | (MAX_SKB_FRAGS, all filled with data)\\n | frag_list-+--\u003e tskb\\n +-----------+ +----------+\\n | frags[0] | (empty! copy failed before filling)\\n +----------+\\n\\nFor SOCK_SEQPACKET with partial data already copied, the error path\\nsaves this message via partial_message for later completion. For\\nSOCK_SEQPACKET, sock_write_iter() automatically sets MSG_EOR, so a\\nsubsequent zero-length write(fd, NULL, 0) completes the message and\\nqueues it to sk_write_queue. kcm_write_msgs() then walks the\\nfrag_list and hits:\\n\\n WARN_ON(!skb_shinfo(skb)-\u003enr_frags)\\n\\nTCP has a similar pattern where skbs are enqueued before data copy\\nand cleaned up on failure via tcp_remove_empty_skb(). KCM was\\nmissing the equivalent cleanup.\\n\\nFix this by tracking the predecessor skb (frag_prev) when allocating\\na new frag_list entry. On error, if the tail skb has zero frags,\\nuse frag_prev to unlink and free it in O(1) without walking the\\nsingly-linked frag_list. frag_prev is safe to dereference because\\nthe entire message chain is only held locally (or in kcm-\u003eseq_skb)\\nand is not added to sk_write_queue until MSG_EOR, so the send path\\ncannot free it underneath us.\\n\\nAlso change the WARN_ON to WARN_ON_ONCE to avoid flooding the log\\nif the condition is somehow hit repeatedly.\\n\\nThere are currently no KCM selftests in the kernel tree; a simple\\nreproducer is available at [1].\\n\\n[1] https://gist.github.com/mrpre/a94d431c757e8d6f168f4dd1a3749daa\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/7af58f76e4b404a74c836881a845e6652db8a09f\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/9ea3671d70ee07480d80bebe86696397c4e99fb7\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/b1e3edf688a88c1a3ac41657055d9c136a08cd25\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/ca220141fa8ebae09765a242076b2b77338106b0\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
}
}
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Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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