{"id":"CVE-2025-39758","title":"In the Linux kernel, the following vulnerability has been resolved:\n\nRDMA/siw: Fix the sendmsg byte count in siw_tcp_sendpages\n\nEver since commit c2ff29e99a76 (\"siw: Inline do_tcp_sendpages()\"),\nwe have been doing this:\n\nstatic int siw_t…","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nRDMA/siw: Fix the sendmsg byte count in siw_tcp_sendpages\n\nEver since commit c2ff29e99a76 (\"siw: Inline do_tcp_sendpages()\"),\nwe have been doing this:\n\nstatic int siw_t…","severity":"critical","cvss":9.8,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","vendor":"linux","product":"linux_kernel","affected":["linux_kernel >= 6.5, < 6.6.103","linux_kernel >= 6.7, < 6.12.43","linux_kernel >= 6.13, < 6.15.11","linux_kernel >= 6.16, < 6.16.2"],"patched":["linux_kernel 6.16.2"],"published":"2025-09-11","updated":"2026-08-23","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2025-39758","references":[{"url":"https://git.kernel.org/stable/c/42ebc16d9d2563f1a1ce0f05b643ee68d54fabf8","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/5661fdd218c2799001b88c17acd19f4395e4488e","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/673cf582fd788af12cdacfb62a6a593083542481","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/b47c4b7cb78b6382c6d1af0bfc0d8218e4f445cc","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/c18646248fed07683d4cee8a8af933fc4fe83c0d","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/edf82bc8150570167a33a7d54627d66614cbf841","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"tags":["nvd"],"epss":0.00404,"epssPercentile":0.34469,"ingestedAt":"2026-08-23T13:48:04.749Z","slug":"CVE-2025-39758","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nRDMA/siw: Fix the sendmsg byte count in siw_tcp_sendpages\n\nEver since commit c2ff29e99a76 (\"siw: Inline do_tcp_sendpages()\"),\nwe have been doing this:\n\nstatic int siw_tcp_sendpages(struct socket *s, struct page **page, int offset,\n                             size_t size)\n[...]\n        /* Calculate the number of bytes we need to push, for this page\n         * specifically */\n        size_t bytes = min_t(size_t, PAGE_SIZE - offset, size);\n        /* If we can't splice it, then copy it in, as normal */\n        if (!sendpage_ok(page[i]))\n                msg.msg_flags &= ~MSG_SPLICE_PAGES;\n        /* Set the bvec pointing to the page, with len $bytes */\n        bvec_set_page(&bvec, page[i], bytes, offset);\n        /* Set the iter to $size, aka the size of the whole sendpages (!!!) */\n        iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, size);\ntry_page_again:\n        lock_sock(sk);\n        /* Sendmsg with $size size (!!!) */\n        rv = tcp_sendmsg_locked(sk, &msg, size);\n\nThis means we've been sending oversized iov_iters and tcp_sendmsg calls\nfor a while. This has a been a benign bug because sendpage_ok() always\nreturned true. With the recent slab allocator changes being slowly\nintroduced into next (that disallow sendpage on large kmalloc\nallocations), we have recently hit out-of-bounds crashes, due to slight\ndifferences in iov_iter behavior between the MSG_SPLICE_PAGES and\n\"regular\" copy paths:\n\n(MSG_SPLICE_PAGES)\nskb_splice_from_iter\n  iov_iter_extract_pages\n    iov_iter_extract_bvec_pages\n      uses i->nr_segs to correctly stop in its tracks before OoB'ing everywhere\n  skb_splice_from_iter gets a \"short\" read\n\n(!MSG_SPLICE_PAGES)\nskb_copy_to_page_nocache copy=iov_iter_count\n [...]\n   copy_from_iter\n        /* this doesn't help */\n        if (unlikely(iter->count < len))\n                len = iter->count;\n          iterate_bvec\n            ... and we run off the bvecs\n\nFix this by properly setting the iov_iter's byte count, plus sending the\ncorrect byte count to tcp_sendmsg_locked.\n\n## Affected\n\n- `linux_kernel >= 6.5, < 6.6.103`\n- `linux_kernel >= 6.7, < 6.12.43`\n- `linux_kernel >= 6.13, < 6.15.11`\n- `linux_kernel >= 6.16, < 6.16.2`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `linux_kernel 6.16.2`","depth":"midnight","depthScore":54,"depthScoreParts":{"impact":53.9,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}