{"id":"CVE-2026-99033","summary":"net/packet: guard the ll header push in packet_rcv_spkt()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/packet: guard the ll header push in packet_rcv_spkt()\n\npacket_rcv_spkt() restores the link layer header with\n\n\tskb_push(skb, skb-\u003edata - skb_mac_header(skb));\n\nThat subtraction is only meaningful when the device actually has a link\nlayer header.  packet_rcv() and tpacket_rcv() both wrap it in\ndev_has_header(), which is also the predicate the block comment at the\ntop of the file states the restore in terms of; packet_rcv_spkt() does\nnot.  commit d549699048b4 (\"net/packet: fix packet receive on L3\ndevices without visible hard header\") introduced the helper and changed\nthe two call sites, and this one stayed behind.\n\nA device without a visible ll header can leave skb-\u003emac_header at the\n0xFFFF sentinel that __alloc_skb() initialises it to.  A CAN skb does:\ninit_can_skb() sets pkt_type and ip_summed but does not reset the\nheaders, and commit 9f10374bb024 (\"can: remove private CAN skb\nheadroom infrastructure\") dropped the skb_reset_*_header() calls that\nused to be there.  skb_mac_header() is then 0xFFFF, the length becomes\na large negative number and skb_push() reports it through\nskb_under_panic() -- from softirq context, so it is a full system panic\neven with panic_on_oops=0:\n\n  skbuff: skb_under_panic: text:ffffffff8bd21bc1 len:-65455 put:-65471 head:... data:... tail:0x50 end:0x180 dev:can0\n  kernel BUG at net/core/skbuff.c:214!\n  RIP: 0010:skb_panic+0x50/0x60\n  Call Trace:\n   \u003cIRQ\u003e\n   skb_push+0x38/0x40\n   packet_rcv_spkt+0xe1/0x170\n   __netif_receive_skb_core.constprop.0+0x7e8/0xd30\n   ...\n  Kernel panic - not syncing: Fatal exception in interrupt\n\nThe socket type is reachable: packet_create() accepts SOCK_PACKET\nalongside SOCK_RAW and SOCK_DGRAM behind the same CAP_NET_RAW check,\nand neither the socket length nor a capability check keeps it away\nfrom a CAN interface.\n\nThe missing skb_reset_*_header() calls in init_can_skb() are a\nregression in their own right and are being fixed separately, but a\npacket socket should not turn a link layer that did not initialise its\nmac header into a kernel panic.  Guard the push the way the other two\nreceive paths do.\n\nTested on v7.3-rc5 under QEMU with a slcan device on a pty, which is\nthe driver RX path: vcan does not reproduce it, because can_send()\nresets the headers on the way out.  One SOCK_PACKET socket bound to\ncan0 and one frame written into the line discipline panics an\nunpatched kernel with the trace above; the same image with this patch\nprints no panic and powers off normally.  Both kernels are this tree,\ndefconfig plus CONFIG_CAN_SLCAN=y, differing only in this hunk.","modified":"2026-11-01T02:30:53.137934995Z","published":"2026-10-23T12:21:37.662Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/99xxx/CVE-2026-99033.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/00fbf71e74115f7628fc0880b855434b1e70c40c"},{"type":"WEB","url":"https://git.kernel.org/stable/c/28bc1ef699610ee09ce3d46a00552f5a0a0144bd"},{"type":"WEB","url":"https://git.kernel.org/stable/c/31c7b15b3716e8d0dad58d2c3cdf321dfd06f4be"},{"type":"WEB","url":"https://git.kernel.org/stable/c/3efe0e0944157fdd2072b4dc7eb0491a317ed272"},{"type":"WEB","url":"https://git.kernel.org/stable/c/48aa1155fa8d83362fc33d02d527a3c3fe40ce1c"},{"type":"WEB","url":"https://git.kernel.org/stable/c/7f84ed94ccfe36091234a2891b88356dc06e6d66"},{"type":"WEB","url":"https://git.kernel.org/stable/c/b880df0e487caa85c3c7ffda37dcd05334b1aa80"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d8a24b9e1774a93943caf68d48c5e17be432220b"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/99xxx/CVE-2026-99033.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-99033"},{"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":"d549699048b4b5c22dd710455bcdb76966e55aa3"},{"fixed":"48aa1155fa8d83362fc33d02d527a3c3fe40ce1c"},{"fixed":"7f84ed94ccfe36091234a2891b88356dc06e6d66"},{"fixed":"b880df0e487caa85c3c7ffda37dcd05334b1aa80"},{"fixed":"d8a24b9e1774a93943caf68d48c5e17be432220b"},{"fixed":"31c7b15b3716e8d0dad58d2c3cdf321dfd06f4be"},{"fixed":"3efe0e0944157fdd2072b4dc7eb0491a317ed272"},{"fixed":"00fbf71e74115f7628fc0880b855434b1e70c40c"},{"fixed":"28bc1ef699610ee09ce3d46a00552f5a0a0144bd"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"5.9.13"},{"fixed":"5.10"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"dadddde259a19105ee69e788835f4d4552767aa9"}]}],"versions":["v5.9.16","v5.9.15","v5.9.14","v5.9.13"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-99033.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.10.0"},{"fixed":"5.10.273"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.224"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.191"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.160"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.113"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.57"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.11"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-99033.json"}}],"schema_version":"1.9.2"}