{ "schema_version": "1.6.1", "id": "RPI-CVE-2024-36933", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2024-36933" ], "published": "2024-05-30T15:29:45Z", "summary": "nsh: Restore skb->{protocol,data,mac_header} for outer header in nsh_gso_segment().", "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnsh: Restore skb->{protocol,data,mac_header} for outer header in nsh_gso_segment().\n\nsyzbot triggered various splats (see [0] and links) by a crafted GSO\npacket of VIRTIO_NET_HDR_GSO_UDP layering the following protocols:\n\n ETH_P_8021AD + ETH_P_NSH + ETH_P_IPV6 + IPPROTO_UDP\n\nNSH can encapsulate IPv4, IPv6, Ethernet, NSH, and MPLS. As the inner\nprotocol can be Ethernet, NSH GSO handler, nsh_gso_segment(), calls\nskb_mac_gso_segment() to invoke inner protocol GSO handlers.\n\nnsh_gso_segment() does the following for the original skb before\ncalling skb_mac_gso_segment()\n\n 1. reset skb->network_header\n 2. save the original skb->{mac_heaeder,mac_len} in a local variable\n 3. pull the NSH header\n 4. resets skb->mac_header\n 5. set up skb->mac_len and skb->protocol for the inner protocol.\n\nand does the following for the segmented skb\n\n 6. set ntohs(ETH_P_NSH) to skb->protocol\n 7. push the NSH header\n 8. restore skb->mac_header\n 9. set skb->mac_header + mac_len to skb->network_header\n 10. restore skb->mac_len\n\nThere are two problems in 6-7 and 8-9.\n\n (a)\n After 6 & 7, skb->data points to the NSH header, so the outer header\n (ETH_P_8021AD in this case) is stripped when skb is sent out of netdev.\n\n Also, if NSH is encapsulated by NSH + Ethernet (so NSH-Ethernet-NSH),\n skb_pull() in the first nsh_gso_segment() will make skb->data point\n to the middle of the outer NSH or Ethernet header because the Ethernet\n header is not pulled by the second nsh_gso_segment().\n\n (b)\n While restoring skb->{mac_header,network_header} in 8 & 9,\n nsh_gso_segment() does not assume that the data in the linear\n buffer is shifted.\n\n However, udp6_ufo_fragment() could shift the data and change\n skb->mac_header accordingly as demonstrated by syzbot.\n\n If this happens, even the restored skb->mac_header points to\n the middle of the outer header.\n\nIt seems nsh_gso_segment() has never worked with outer headers so far.\n\nAt the end of nsh_gso_segment(), the outer header must be restored for\nthe segmented skb, instead of the NSH header.\n\nTo do that, let's calculate the outer header position relatively from\nthe inner header and set skb->{data,mac_header,protocol} properly.\n\n[0]:\nBUG: KMSAN: uninit-value in ipvlan_process_outbound drivers/net/ipvlan/ipvlan_core.c:524 [inline]\nBUG: KMSAN: uninit-value in ipvlan_xmit_mode_l3 drivers/net/ipvlan/ipvlan_core.c:602 [inline]\nBUG: KMSAN: uninit-value in ipvlan_queue_xmit+0xf44/0x16b0 drivers/net/ipvlan/ipvlan_core.c:668\n ipvlan_process_outbound drivers/net/ipvlan/ipvlan_core.c:524 [inline]\n ipvlan_xmit_mode_l3 drivers/net/ipvlan/ipvlan_core.c:602 [inline]\n ipvlan_queue_xmit+0xf44/0x16b0 drivers/net/ipvlan/ipvlan_core.c:668\n ipvlan_start_xmit+0x5c/0x1a0 drivers/net/ipvlan/ipvlan_main.c:222\n __netdev_start_xmit include/linux/netdevice.h:4989 [inline]\n netdev_start_xmit include/linux/netdevice.h:5003 [inline]\n xmit_one net/core/dev.c:3547 [inline]\n dev_hard_start_xmit+0x244/0xa10 net/core/dev.c:3563\n __dev_queue_xmit+0x33ed/0x51c0 net/core/dev.c:4351\n dev_queue_xmit include/linux/netdevice.h:3171 [inline]\n packet_xmit+0x9c/0x6b0 net/packet/af_packet.c:276\n packet_snd net/packet/af_packet.c:3081 [inline]\n packet_sendmsg+0x8aef/0x9f10 net/packet/af_packet.c:3113\n sock_sendmsg_nosec net/socket.c:730 [inline]\n __sock_sendmsg net/socket.c:745 [inline]\n __sys_sendto+0x735/0xa10 net/socket.c:2191\n __do_sys_sendto net/socket.c:2203 [inline]\n __se_sys_sendto net/socket.c:2199 [inline]\n __x64_sys_sendto+0x125/0x1c0 net/socket.c:2199\n do_syscall_x64 arch/x86/entry/common.c:52 [inline]\n do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83\n entry_SYSCALL_64_after_hwframe+0x63/0x6b\n\nUninit was created at:\n slab_post_alloc_hook mm/slub.c:3819 [inline]\n slab_alloc_node mm/slub.c:3860 [inline]\n __do_kmalloc_node mm/slub.c:3980 [inline]\n __kmalloc_node_track_caller+0x705/0x1000 mm/slub.c:4001\n kmalloc_reserve+0x249/0x4a0 net/core/skbuff.c:582\n __\n---truncated---", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H" } ], "affected": [ { "package": { "ecosystem": "Raspberry Pi OS:12", "name": "linux" }, "versions": [ "1:6.1.21-1+rpt1", "1:6.1.47-1+rpt2", "1:6.1.47-1+rpt4", "1:6.1.54-1+rpt2", "1:6.1.58-1+rpt2", "1:6.1.63-1+rpt1", "1:6.1.73-1+rpt1", 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"linux_commit": null, "upstream_version": "6.1.63", "assessment": "upstream version (no usable Linux commit)", "upstream_fixed": "6.1.91" }, "1:6.1.73-1+rpt1": { "linux_commit": null, "upstream_version": "6.1.73", "assessment": "upstream version (no usable Linux commit)", "upstream_fixed": "6.1.91" }, "1:6.6.20-1+rpt1": { "linux_commit": "6f16847710cc0502450788b9f12f0a14d3429668", "upstream_version": "6.6.20", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.6.31" }, "1:6.6.28-1+rpt1": { "linux_commit": "0c341f47adc3578cd5f817aa20ee2b7f9ae6b23e", "upstream_version": "6.6.28", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.6.31" } } } } ], "references": [ { "type": "ADVISORY", "url": "https://www.cve.org/CVERecord?id=CVE-2024-36933" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/a7c2c3c1caabcb4a3d6c47284c397507aaf54fe9" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/46134031c20fd313d03b90169d64b2e05ca6b65c" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/bbccf0caef2fa917d6d0692385a06ce3c262a216" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/5a4603fbc285752d19e4b415466db18ef3617e4a" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/37ed6f244ec5bda2e90b085084e322ea55d0aaa2" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/696d18bb59727a2e0526c0802a812620be1c9340" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/29a07f2ee4d273760c2acbfc756e29eccd82470a" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/4b911a9690d72641879ea6d13cce1de31d346d79" } ], "database_specific": { "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-08-05T11:52:36Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 7.8, "cvss_v3_severity": "High", "scenario": "AV:L - The vulnerable path is entered from `packet_sendmsg()` on a local AF_PACKET socket using PACKET_VNET_HDR to hand the stack a crafted ETH_P_8021AD/ETH_P_NSH/IPv6/UDP GSO skb. NSH has no GRO/receive-offload handler, so a remote peer cannot cause the kernel to construct an NSH-typed GSO skb with an outer header; the trigger must be locally injected.\nAC:L - The attacker fully controls the packet layering, the outer header length and the GSO parameters, so the broken header restore is hit deterministically on every send \u2014 syzbot produced C reproducers for both reported splats. No race, timing window or uncontrollable memory layout is involved.\nPR:L - Sending the crafted GSO frame requires only a raw packet socket (CAP_NET_RAW), which an unprivileged user obtains inside a user+network namespace via `unshare -Urn`, and the nsh offload handler can be autoloaded unprivileged through the openvswitch generic-netlink family alias (`ctrl_getfamily()` calls `request_module()` with no capability check). No real root or init-namespace privilege is needed.\nUI:N - The attacker triggers the entire sequence himself with a single sendto() on his own socket. No victim action, mount, or file open is required.\nS:U - The corruption is confined to kernel skb metadata and buffers handled by the same kernel security authority. No VM, IOMMU, or sandbox boundary is crossed.\nC:H - Each segment's `mac_header`/`network_header` are set to offsets belonging to a different skb, so the kernel reads uninitialized/stale heap headroom and interprets it as the outer Ethernet header (KMSAN uninit-value in `ipvlan_process_outbound` reading `ethh->h_dest`); those recycled heap bytes steer routing and can be emitted on the wire, and the negative `skb_network_offset()` extends reads outside the packet data rather than confining them to a small bounded field.\nI:H - The skb geometry corruption makes the kernel write protocol header fields (IPv6 `payload_len`, `nexthdr`) at mis-located offsets and transmit frames whose outer 802.1AD/Ethernet header has been stripped or truncated, letting an attacker punch packets out with framing the stack never intended and defeating VLAN-based segmentation; corrupted header offsets fed to NIC offload descriptors extend this to attacker-influenced buffer regions.\nA:H - syzbot reproduced kernel splats on this path (KMSAN uninit-value via `ipvlan_queue_xmit` and a `WARNING in gre_tap_xmit` from `pskb_inet_may_pull()` on a wrapped length), which panic the machine under panic_on_warn, and the unchecked `__skb_push()` plus negative `skb_network_offset()` arithmetic can drive downstream `skb_pull()`/`skb_push()` into `BUG_ON(skb->len < skb->data_len)` / `skb_under_panic()`. The attacker can repeat the send in a loop." } } }