{"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":"2026-05-11T22:20:47.856Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-05-11T22:20:47.856Z"},"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":"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":"6.12.75","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":"6.12.75"},{"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/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"}}}}