{"id":"AZL-67157","summary":"CVE-2025-39758 affecting package kernel for versions less than 6.6.104.2-1","details":"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_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-\u003enr_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-\u003ecount \u003c len))\n                len = iter-\u003ecount;\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.","modified":"2026-04-01T05:21:08.275255Z","published":"2025-09-11T17:15:39Z","upstream":["CVE-2025-39758"],"references":[{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-39758"}],"affected":[{"package":{"name":"kernel","ecosystem":"Azure Linux:3","purl":"pkg:rpm/azure-linux/kernel"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.6.104.2-1"}]}],"database_specific":{"source":"https://github.com/microsoft/AzureLinuxVulnerabilityData/blob/main/osv/AZL-67157.json"}}],"schema_version":"1.7.5"}