{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-43244", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-05-01T14:12:55.995Z", "datePublished": "2026-05-06T11:28:36.946Z", "dateUpdated": "2026-10-21T12:40:22.099Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-21T12:40:22.099Z" }, "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-+--> 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)->nr_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->seq_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" } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/kcm/kcmsock.c" ], "versions": [ { "version": "ab7ac4eb9832e32a09f4e8042705484d2fb0aad3", "lessThan": "6f129a251c2795ba55dd5cc1fdf7e0af3098d848", "status": "affected", "versionType": "git" }, { "version": "ab7ac4eb9832e32a09f4e8042705484d2fb0aad3", "lessThan": "9ea3671d70ee07480d80bebe86696397c4e99fb7", "status": "affected", "versionType": "git" }, { "version": "ab7ac4eb9832e32a09f4e8042705484d2fb0aad3", "lessThan": "b1e3edf688a88c1a3ac41657055d9c136a08cd25", "status": "affected", "versionType": "git" }, { "version": "ab7ac4eb9832e32a09f4e8042705484d2fb0aad3", "lessThan": "7af58f76e4b404a74c836881a845e6652db8a09f", "status": "affected", "versionType": "git" }, { "version": "ab7ac4eb9832e32a09f4e8042705484d2fb0aad3", "lessThan": "ca220141fa8ebae09765a242076b2b77338106b0", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/kcm/kcmsock.c" ], "versions": [ { "version": "4.6", "status": "affected" }, { "version": "0", "lessThan": "4.6", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.160", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.75", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.16", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.19.6", "lessThanOrEqual": "6.19.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.0", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.6", "versionEndExcluding": "6.6.160" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.6", "versionEndExcluding": "6.12.75" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.6", "versionEndExcluding": "6.18.16" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.6", "versionEndExcluding": "6.19.6" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.6", "versionEndExcluding": "7.0" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/6f129a251c2795ba55dd5cc1fdf7e0af3098d848" }, { "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": { "engine": "bippy-1.2.0" } } } }