{"id":"CVE-2026-31649","summary":"net: stmmac: fix integer underflow in chain mode","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: stmmac: fix integer underflow in chain mode\n\nThe jumbo_frm() chain-mode implementation unconditionally computes\n\n    len = nopaged_len - bmax;\n\nwhere nopaged_len = skb_headlen(skb) (linear bytes only) and bmax is\nBUF_SIZE_8KiB or BUF_SIZE_2KiB.  However, the caller stmmac_xmit()\ndecides to invoke jumbo_frm() based on skb-\u003elen (total length including\npage fragments):\n\n    is_jumbo = stmmac_is_jumbo_frm(priv, skb-\u003elen, enh_desc);\n\nWhen a packet has a small linear portion (nopaged_len \u003c= bmax) but a\nlarge total length due to page fragments (skb-\u003elen \u003e bmax), the\nsubtraction wraps as an unsigned integer, producing a huge len value\n(~0xFFFFxxxx).  This causes the while (len != 0) loop to execute\nhundreds of thousands of iterations, passing skb-\u003edata + bmax * i\npointers far beyond the skb buffer to dma_map_single().  On IOMMU-less\nSoCs (the typical deployment for stmmac), this maps arbitrary kernel\nmemory to the DMA engine, constituting a kernel memory disclosure and\npotential memory corruption from hardware.\n\nFix this by introducing a buf_len local variable clamped to\nmin(nopaged_len, bmax).  Computing len = nopaged_len - buf_len is then\nalways safe: it is zero when the linear portion fits within a single\ndescriptor, causing the while (len != 0) loop to be skipped naturally,\nand the fragment loop in stmmac_xmit() handles page fragments afterward.","modified":"2026-05-27T08:29:30.026454093Z","published":"2026-04-24T14:45:02.520Z","related":["SUSE-SU-2026:2068-1"],"database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31649.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/10d12b9240ebf96c785f0e2e4228318cd5f3a3eb"},{"type":"WEB","url":"https://git.kernel.org/stable/c/275bdf762e82082f064e60a92448fa2ac43cf95b"},{"type":"WEB","url":"https://git.kernel.org/stable/c/2c91b39912278d0878f9ba60ba04d2518b18a08d"},{"type":"WEB","url":"https://git.kernel.org/stable/c/513e06735f5be575b409d195822195348b164e48"},{"type":"WEB","url":"https://git.kernel.org/stable/c/51f4e090b9f87b40c21b6daadb5c06e6c0a07b67"},{"type":"WEB","url":"https://git.kernel.org/stable/c/6fca757c20396dc2e604dcc61922264e9e3dc803"},{"type":"WEB","url":"https://git.kernel.org/stable/c/a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f"},{"type":"WEB","url":"https://git.kernel.org/stable/c/b7b8012193fd98236d7ae05d4b553f010a77b2ef"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31649.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-31649"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"286a837217204b1ef105e3a554d0757e4fdfaac1"},{"fixed":"513e06735f5be575b409d195822195348b164e48"},{"fixed":"275bdf762e82082f064e60a92448fa2ac43cf95b"},{"fixed":"a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f"},{"fixed":"b7b8012193fd98236d7ae05d4b553f010a77b2ef"},{"fixed":"2c91b39912278d0878f9ba60ba04d2518b18a08d"},{"fixed":"6fca757c20396dc2e604dcc61922264e9e3dc803"},{"fixed":"10d12b9240ebf96c785f0e2e4228318cd5f3a3eb"},{"fixed":"51f4e090b9f87b40c21b6daadb5c06e6c0a07b67"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-31649.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"3.2.0"},{"fixed":"5.10.253"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.203"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.169"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.135"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.82"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.23"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"6.19.13"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-31649.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"}]}