{"id":"CVE-2026-99033","title":"net/packet: guard the ll header push in packet_rcv_spkt()","summary":"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->data - skb_mac_header(skb));\n\nThat…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 < d8a24b9e1774a93943caf68d48c5e17be432220b","Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 < 31c7b15b3716e8d0dad58d2c3cdf321dfd06f4be","Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 < 3efe0e0944157fdd2072b4dc7eb0491a317ed272","Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 < 00fbf71e74115f7628fc0880b855434b1e70c40c","Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 < 28bc1ef699610ee09ce3d46a00552f5a0a0144bd","Linux dadddde259a19105ee69e788835f4d4552767aa9","Linux >= 5.9.13 < 5.10","Linux 5.10"],"published":"2026-10-23","updated":"2026-10-23","sourceUpdated":"2026-10-23T12:21:37.662Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-99033","references":[{"url":"https://git.kernel.org/stable/c/d8a24b9e1774a93943caf68d48c5e17be432220b"},{"url":"https://git.kernel.org/stable/c/31c7b15b3716e8d0dad58d2c3cdf321dfd06f4be"},{"url":"https://git.kernel.org/stable/c/3efe0e0944157fdd2072b4dc7eb0491a317ed272"},{"url":"https://git.kernel.org/stable/c/00fbf71e74115f7628fc0880b855434b1e70c40c"},{"url":"https://git.kernel.org/stable/c/28bc1ef699610ee09ce3d46a00552f5a0a0144bd"}],"tags":["cve.org"],"ingestedAt":"2026-10-23T13:24:55.531Z","slug":"CVE-2026-99033","body":"## Overview\n\nIn 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->data - 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->mac_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   <IRQ>\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.\n\n## Affected\n\n- `Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 < d8a24b9e1774a93943caf68d48c5e17be432220b`\n- `Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 < 31c7b15b3716e8d0dad58d2c3cdf321dfd06f4be`\n- `Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 < 3efe0e0944157fdd2072b4dc7eb0491a317ed272`\n- `Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 < 00fbf71e74115f7628fc0880b855434b1e70c40c`\n- `Linux >= d549699048b4b5c22dd710455bcdb76966e55aa3 < 28bc1ef699610ee09ce3d46a00552f5a0a0144bd`\n- `Linux dadddde259a19105ee69e788835f4d4552767aa9`\n- `Linux >= 5.9.13 < 5.10`\n- `Linux 5.10`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}