ghsa-jj9v-ff2v-cgx9
Vulnerability from github
Published
2024-04-04 09:30
Modified
2024-11-12 18:30
Details

In 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.

Show details on source website


{
  "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"
    }
  ]
}


Log in or create an account to share your comment.




Tags
Taxonomy of the tags.


Loading...

Loading...

Loading...

Sightings

Author Source Type Date

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
  • Confirmed: The vulnerability is confirmed from an analyst perspective.
  • Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
  • Patched: This vulnerability was successfully patched by the user reporting the sighting.
  • Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
  • Not confirmed: The user expresses doubt about the veracity of the vulnerability.
  • Not patched: This vulnerability was not successfully patched by the user reporting the sighting.