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CVE-2025-39758

Estado: ModificadaMedia (5.5)—

In the Linux kernel, the following vulnerability has been resolved:

RDMA/siw: Fix the sendmsg byte count in siw_tcp_sendpages

Ever since commit c2ff29e99a76 ("siw: Inline do_tcp_sendpages()"), we have been doing this:

This means we've been sending oversized iov_iters and tcp_sendmsg calls for a while. This has a been a benign bug because sendpage_ok() always returned true. With the recent slab allocator changes being slowly introduced into next (that disallow sendpage on large kmalloc allocations), we have recently hit out-of-bounds crashes, due to slight differences in iov_iter behavior between the MSG_SPLICE_PAGES and "regular" copy paths:

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Fix this by properly setting the iov_iter's byte count, plus sending the correct byte count to tcp_sendmsg_locked.

Detalles técnicos trazas, registros y código del informe original
static int siw_tcp_sendpages(struct socket *s, struct page **page, int offset,
                             size_t size)
[...]
        /* Calculate the number of bytes we need to push, for this page
         * specifically */
        size_t bytes = min_t(size_t, PAGE_SIZE - offset, size);
        /* If we can't splice it, then copy it in, as normal */
        if (!sendpage_ok(page[i]))
                msg.msg_flags &= ~MSG_SPLICE_PAGES;
        /* Set the bvec pointing to the page, with len $bytes */
        bvec_set_page(&bvec, page[i], bytes, offset);
        /* Set the iter to $size, aka the size of the whole sendpages (!!!) */
        iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, size);
try_page_again:
        lock_sock(sk);
        /* Sendmsg with $size size (!!!) */
        rv = tcp_sendmsg_locked(sk, &msg, size);

(MSG_SPLICE_PAGES)
skb_splice_from_iter
  iov_iter_extract_pages
    iov_iter_extract_bvec_pages
      uses i->nr_segs to correctly stop in its tracks before OoB'ing everywhere
  skb_splice_from_iter gets a "short" read

(!MSG_SPLICE_PAGES)
skb_copy_to_page_nocache copy=iov_iter_count
 [...]
   copy_from_iter
        /* this doesn't help */
        if (unlikely(iter->count < len))
                len = iter->count;
          iterate_bvec
            ... and we run off the bvecs

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

Referencias

JSON original (NVD)

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  "id": "CVE-2025-39758",
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  "descriptions": [
    {
      "lang": "en",
      "value": "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->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."
    }
  ],
  "lastModified": "2026-08-23T13:16:26.380",
  "configurations": [
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