GHSA-JJ9V-FF2V-CGX9
Vulnerability from github – Published: 2024-04-04 09:30 – Updated: 2024-11-12 18:30In the Linux kernel, the following vulnerability has been resolved:
net: ip_tunnel: prevent perpetual headroom growth
syzkaller triggered following kasan splat: BUG: KASAN: use-after-free in __skb_flow_dissect+0x19d1/0x7a50 net/core/flow_dissector.c:1170 Read of size 1 at addr ffff88812fb4000e by task syz-executor183/5191 [..] kasan_report+0xda/0x110 mm/kasan/report.c:588 __skb_flow_dissect+0x19d1/0x7a50 net/core/flow_dissector.c:1170 skb_flow_dissect_flow_keys include/linux/skbuff.h:1514 [inline] skbget_hash net/core/flow_dissector.c:1791 [inline] skb_get_hash+0xc7/0x540 net/core/flow_dissector.c:1856 skb_get_hash include/linux/skbuff.h:1556 [inline] ip_tunnel_xmit+0x1855/0x33c0 net/ipv4/ip_tunnel.c:748 ipip_tunnel_xmit+0x3cc/0x4e0 net/ipv4/ipip.c:308 __netdev_start_xmit include/linux/netdevice.h:4940 [inline] netdev_start_xmit include/linux/netdevice.h:4954 [inline] xmit_one net/core/dev.c:3548 [inline] dev_hard_start_xmit+0x13d/0x6d0 net/core/dev.c:3564 __dev_queue_xmit+0x7c1/0x3d60 net/core/dev.c:4349 dev_queue_xmit include/linux/netdevice.h:3134 [inline] neigh_connected_output+0x42c/0x5d0 net/core/neighbour.c:1592 ... ip_finish_output2+0x833/0x2550 net/ipv4/ip_output.c:235 ip_finish_output+0x31/0x310 net/ipv4/ip_output.c:323 .. iptunnel_xmit+0x5b4/0x9b0 net/ipv4/ip_tunnel_core.c:82 ip_tunnel_xmit+0x1dbc/0x33c0 net/ipv4/ip_tunnel.c:831 ipgre_xmit+0x4a1/0x980 net/ipv4/ip_gre.c:665 __netdev_start_xmit include/linux/netdevice.h:4940 [inline] netdev_start_xmit include/linux/netdevice.h:4954 [inline] xmit_one net/core/dev.c:3548 [inline] dev_hard_start_xmit+0x13d/0x6d0 net/core/dev.c:3564 ...
The splat occurs because skb->data points past skb->head allocated area. This is because neigh layer does: __skb_pull(skb, skb_network_offset(skb));
... but skb_network_offset() returns a negative offset and __skb_pull() arg is unsigned. IOW, we skb->data gets "adjusted" by a huge value.
The negative value is returned because skb->head and skb->data distance is more than 64k and skb->network_header (u16) has wrapped around.
The bug is in the ip_tunnel infrastructure, which can cause dev->needed_headroom to increment ad infinitum.
The syzkaller reproducer consists of packets getting routed via a gre tunnel, and route of gre encapsulated packets pointing at another (ipip) tunnel. The ipip encapsulation finds gre0 as next output device.
This results in the following pattern:
1). First packet is to be sent out via gre0. Route lookup found an output device, ipip0.
2). ip_tunnel_xmit for gre0 bumps gre0->needed_headroom based on the future output device, rt.dev->needed_headroom (ipip0).
3). ip output / start_xmit moves skb on to ipip0. which runs the same code path again (xmit recursion).
4). Routing step for the post-gre0-encap packet finds gre0 as output device to use for ipip0 encapsulated packet.
tunl0->needed_headroom is then incremented based on the (already bumped) gre0 device headroom.
This repeats for every future packet:
gre0->needed_headroom gets inflated because previous packets' ipip0 step incremented rt->dev (gre0) headroom, and ipip0 incremented because gre0 needed_headroom was increased.
For each subsequent packet, gre/ipip0->needed_headroom grows until post-expand-head reallocations result in a skb->head/data distance of more than 64k.
Once that happens, skb->network_header (u16) wraps around when pskb_expand_head tries to make sure that skb_network_offset() is unchanged after the headroom expansion/reallocation.
After this skb_network_offset(skb) returns a different (and negative) result post headroom expansion.
The next trip to neigh layer (or anything else that would __skb_pull the network header) makes skb->data point to a memory location outside skb->head area.
v2: Cap the needed_headroom update to an arbitarily chosen upperlimit to prevent perpetual increase instead of dropping the headroom increment completely.
{
"affected": [],
"aliases": [
"CVE-2024-26804"
],
"database_specific": {
"cwe_ids": [
"CWE-416"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-04-04T09:15:09Z",
"severity": "MODERATE"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ip_tunnel: prevent perpetual headroom growth\n\nsyzkaller triggered following kasan splat:\nBUG: KASAN: use-after-free in __skb_flow_dissect+0x19d1/0x7a50 net/core/flow_dissector.c:1170\nRead of size 1 at addr ffff88812fb4000e by task syz-executor183/5191\n[..]\n kasan_report+0xda/0x110 mm/kasan/report.c:588\n __skb_flow_dissect+0x19d1/0x7a50 net/core/flow_dissector.c:1170\n skb_flow_dissect_flow_keys include/linux/skbuff.h:1514 [inline]\n ___skb_get_hash net/core/flow_dissector.c:1791 [inline]\n __skb_get_hash+0xc7/0x540 net/core/flow_dissector.c:1856\n skb_get_hash include/linux/skbuff.h:1556 [inline]\n ip_tunnel_xmit+0x1855/0x33c0 net/ipv4/ip_tunnel.c:748\n ipip_tunnel_xmit+0x3cc/0x4e0 net/ipv4/ipip.c:308\n __netdev_start_xmit include/linux/netdevice.h:4940 [inline]\n netdev_start_xmit include/linux/netdevice.h:4954 [inline]\n xmit_one net/core/dev.c:3548 [inline]\n dev_hard_start_xmit+0x13d/0x6d0 net/core/dev.c:3564\n __dev_queue_xmit+0x7c1/0x3d60 net/core/dev.c:4349\n dev_queue_xmit include/linux/netdevice.h:3134 [inline]\n neigh_connected_output+0x42c/0x5d0 net/core/neighbour.c:1592\n ...\n ip_finish_output2+0x833/0x2550 net/ipv4/ip_output.c:235\n ip_finish_output+0x31/0x310 net/ipv4/ip_output.c:323\n ..\n iptunnel_xmit+0x5b4/0x9b0 net/ipv4/ip_tunnel_core.c:82\n ip_tunnel_xmit+0x1dbc/0x33c0 net/ipv4/ip_tunnel.c:831\n ipgre_xmit+0x4a1/0x980 net/ipv4/ip_gre.c:665\n __netdev_start_xmit include/linux/netdevice.h:4940 [inline]\n netdev_start_xmit include/linux/netdevice.h:4954 [inline]\n xmit_one net/core/dev.c:3548 [inline]\n dev_hard_start_xmit+0x13d/0x6d0 net/core/dev.c:3564\n ...\n\nThe splat occurs because skb-\u003edata points past skb-\u003ehead allocated area.\nThis is because neigh layer does:\n __skb_pull(skb, skb_network_offset(skb));\n\n... but skb_network_offset() returns a negative offset and __skb_pull()\narg is unsigned. IOW, we skb-\u003edata gets \"adjusted\" by a huge value.\n\nThe negative value is returned because skb-\u003ehead and skb-\u003edata distance is\nmore than 64k and skb-\u003enetwork_header (u16) has wrapped around.\n\nThe bug is in the ip_tunnel infrastructure, which can cause\ndev-\u003eneeded_headroom to increment ad infinitum.\n\nThe syzkaller reproducer consists of packets getting routed via a gre\ntunnel, and route of gre encapsulated packets pointing at another (ipip)\ntunnel. The ipip encapsulation finds gre0 as next output device.\n\nThis results in the following pattern:\n\n1). First packet is to be sent out via gre0.\nRoute lookup found an output device, ipip0.\n\n2).\nip_tunnel_xmit for gre0 bumps gre0-\u003eneeded_headroom based on the future\noutput device, rt.dev-\u003eneeded_headroom (ipip0).\n\n3).\nip output / start_xmit moves skb on to ipip0. which runs the same\ncode path again (xmit recursion).\n\n4).\nRouting step for the post-gre0-encap packet finds gre0 as output device\nto use for ipip0 encapsulated packet.\n\ntunl0-\u003eneeded_headroom is then incremented based on the (already bumped)\ngre0 device headroom.\n\nThis repeats for every future packet:\n\ngre0-\u003eneeded_headroom gets inflated because previous packets\u0027 ipip0 step\nincremented rt-\u003edev (gre0) headroom, and ipip0 incremented because gre0\nneeded_headroom was increased.\n\nFor each subsequent packet, gre/ipip0-\u003eneeded_headroom grows until\npost-expand-head reallocations result in a skb-\u003ehead/data distance of\nmore than 64k.\n\nOnce that happens, skb-\u003enetwork_header (u16) wraps around when\npskb_expand_head tries to make sure that skb_network_offset() is unchanged\nafter the headroom expansion/reallocation.\n\nAfter this skb_network_offset(skb) returns a different (and negative)\nresult post headroom expansion.\n\nThe next trip to neigh layer (or anything else that would __skb_pull the\nnetwork header) makes skb-\u003edata point to a memory location outside\nskb-\u003ehead area.\n\nv2: Cap the needed_headroom update to an arbitarily chosen upperlimit to\nprevent perpetual increase instead of dropping the headroom increment\ncompletely.",
"id": "GHSA-jj9v-ff2v-cgx9",
"modified": "2024-11-12T18:30:50Z",
"published": "2024-04-04T09:30:36Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-26804"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/049d7989c67e8dd50f07a2096dbafdb41331fb9b"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2e95350fe9db9d53c701075060ac8ac883b68aee"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5ae1e9922bbdbaeb9cfbe91085ab75927488ac0f"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a0a1db40b23e8ff86dea2786c5ea1470bb23ecb9"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ab63de24ebea36fe73ac7121738595d704b66d96"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/afec0c5cd2ed71ca95a8b36a5e6d03333bf34282"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f81e94d2dcd2397137edcb8b85f4c5bed5d22383"
},
{
"type": "WEB",
"url": "https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
"type": "CVSS_V3"
}
]
}
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