{"id":"CVE-2026-31421","summary":"net/sched: cls_fw: fix NULL pointer dereference on shared blocks","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: cls_fw: fix NULL pointer dereference on shared blocks\n\nThe old-method path in fw_classify() calls tcf_block_q() and\ndereferences q-\u003ehandle.  Shared blocks leave block-\u003eq NULL, causing a\nNULL deref when an empty cls_fw filter is attached to a shared block\nand a packet with a nonzero major skb mark is classified.\n\nReject the configuration in fw_change() when the old method (no\nTCA_OPTIONS) is used on a shared block, since fw_classify()'s\nold-method path needs block-\u003eq which is NULL for shared blocks.\n\nThe fixed null-ptr-deref calling stack:\n KASAN: null-ptr-deref in range [0x0000000000000038-0x000000000000003f]\n RIP: 0010:fw_classify (net/sched/cls_fw.c:81)\n Call Trace:\n  tcf_classify (./include/net/tc_wrapper.h:197 net/sched/cls_api.c:1764 net/sched/cls_api.c:1860)\n  tc_run (net/core/dev.c:4401)\n  __dev_queue_xmit (net/core/dev.c:4535 net/core/dev.c:4790)","modified":"2026-07-09T18:31:05.272453272Z","published":"2026-04-13T13:40:25.278Z","related":["SUSE-SU-2026:21834-1","SUSE-SU-2026:21841-1","SUSE-SU-2026:21845-1","SUSE-SU-2026:21860-1","SUSE-SU-2026:21876-1","SUSE-SU-2026:21877-1","SUSE-SU-2026:21916-1","SUSE-SU-2026:21919-1","SUSE-SU-2026:2217-1","SUSE-SU-2026:2238-1","SUSE-SU-2026:2450-1","openSUSE-SU-2026:20826-1"],"database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31421.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28"},{"type":"WEB","url":"https://git.kernel.org/stable/c/3cb055df9e8625ce699a259d8178d67b37f2b160"},{"type":"WEB","url":"https://git.kernel.org/stable/c/3d41f9a314afa94b1c7c7c75405920123220e8cd"},{"type":"WEB","url":"https://git.kernel.org/stable/c/5cf41031922c154aa5ccda8bcdb0f5e6226582ec"},{"type":"WEB","url":"https://git.kernel.org/stable/c/96426c348def662b06bfdc65be3002905604927a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d6d5bd62a09650856e1e2010eb09853eba0d64e1"},{"type":"WEB","url":"https://git.kernel.org/stable/c/faeea8bbf6e958bf3c00cb08263109661975987c"},{"type":"WEB","url":"https://git.kernel.org/stable/c/febf64ca79a2d6540ab6e5e197fa0f4f7e84473e"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31421.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-31421"},{"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":"1abf272022cf1d18469405f47b4ec49c6a3125db"},{"fixed":"d6d5bd62a09650856e1e2010eb09853eba0d64e1"},{"fixed":"febf64ca79a2d6540ab6e5e197fa0f4f7e84473e"},{"fixed":"3d41f9a314afa94b1c7c7c75405920123220e8cd"},{"fixed":"18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28"},{"fixed":"5cf41031922c154aa5ccda8bcdb0f5e6226582ec"},{"fixed":"3cb055df9e8625ce699a259d8178d67b37f2b160"},{"fixed":"96426c348def662b06bfdc65be3002905604927a"},{"fixed":"faeea8bbf6e958bf3c00cb08263109661975987c"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-31421.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"4.15.0"},{"fixed":"5.10.253"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.203"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.168"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.134"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.81"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.22"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"6.19.12"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-31421.json"}}],"schema_version":"1.7.5"}