{"id":"CVE-2026-31421","state":"PUBLISHED","title":"net/sched: cls_fw: fix NULL pointer dereference on shared blocks","description":"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->handle.  Shared blocks leave block->q 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->q 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)","publishedAt":"2026-04-13T13:40:25.278Z","updatedAt":"2026-10-15T01:16:00.824Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"1abf272022cf1d18469405f47b4ec49c6a3125db","status":"affected","lessThan":"d6d5bd62a09650856e1e2010eb09853eba0d64e1","versionType":"git"},{"version":"1abf272022cf1d18469405f47b4ec49c6a3125db","status":"affected","lessThan":"febf64ca79a2d6540ab6e5e197fa0f4f7e84473e","versionType":"git"},{"version":"1abf272022cf1d18469405f47b4ec49c6a3125db","status":"affected","lessThan":"3d41f9a314afa94b1c7c7c75405920123220e8cd","versionType":"git"},{"version":"1abf272022cf1d18469405f47b4ec49c6a3125db","status":"affected","lessThan":"18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28","versionType":"git"},{"version":"1abf272022cf1d18469405f47b4ec49c6a3125db","status":"affected","lessThan":"5cf41031922c154aa5ccda8bcdb0f5e6226582ec","versionType":"git"},{"version":"1abf272022cf1d18469405f47b4ec49c6a3125db","status":"affected","lessThan":"3cb055df9e8625ce699a259d8178d67b37f2b160","versionType":"git"},{"version":"1abf272022cf1d18469405f47b4ec49c6a3125db","status":"affected","lessThan":"96426c348def662b06bfdc65be3002905604927a","versionType":"git"},{"version":"1abf272022cf1d18469405f47b4ec49c6a3125db","status":"affected","lessThan":"faeea8bbf6e958bf3c00cb08263109661975987c","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/cls_fw.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.15","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.15","versionType":"semver"},{"version":"5.10.253","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.203","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.168","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.134","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.81","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.22","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.12","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/cls_fw.c"]}],"references":["https://git.kernel.org/stable/c/d6d5bd62a09650856e1e2010eb09853eba0d64e1","https://git.kernel.org/stable/c/febf64ca79a2d6540ab6e5e197fa0f4f7e84473e","https://git.kernel.org/stable/c/3d41f9a314afa94b1c7c7c75405920123220e8cd","https://git.kernel.org/stable/c/18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28","https://git.kernel.org/stable/c/5cf41031922c154aa5ccda8bcdb0f5e6226582ec","https://git.kernel.org/stable/c/3cb055df9e8625ce699a259d8178d67b37f2b160","https://git.kernel.org/stable/c/96426c348def662b06bfdc65be3002905604927a","https://git.kernel.org/stable/c/faeea8bbf6e958bf3c00cb08263109661975987c","https://cert-portal.siemens.com/productcert/html/ssa-082556.html","https://cert-portal.siemens.com/productcert/html/ssa-019113.html","https://cert-portal.siemens.com/productcert/html/ssa-457936.html"],"weaknesses":[],"ingestedAt":"2026-10-29T20:11:40.391Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/31xxx/CVE-2026-31421.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-31421","state":"PUBLISHED","datePublished":"2026-04-13T13:40:25.278Z","dateUpdated":"2026-10-15T01:16:00.824Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-03-09T15:48:24.088Z"},"containers":{"cna":{"title":"net/sched: cls_fw: fix NULL pointer dereference on shared blocks","descriptions":[{"lang":"en","value":"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->handle.  Shared blocks leave block->q 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->q 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 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