GHSA-F3C9-5Q5H-57M3
Vulnerability from github – Published: 2024-05-19 12:30 – Updated: 2024-05-19 12:30In the Linux kernel, the following vulnerability has been resolved:
net: skbuff: add overflow debug check to pull/push helpers
syzbot managed to trigger following splat: BUG: KASAN: use-after-free in __skb_flow_dissect+0x4a3b/0x5e50 Read of size 1 at addr ffff888208a4000e by task a.out/2313 [..] __skb_flow_dissect+0x4a3b/0x5e50 __skb_get_hash+0xb4/0x400 ip_tunnel_xmit+0x77e/0x26f0 ipip_tunnel_xmit+0x298/0x410 ..
Analysis shows that the skb has a valid ->head, but bogus ->data pointer.
skb->data gets its bogus value via the neigh layer, which does:
1556 __skb_pull(skb, skb_network_offset(skb));
... and the skb was already dodgy at this point:
skb_network_offset(skb) returns a negative value due to an earlier overflow of skb->network_header (u16). __skb_pull thus "adjusts" skb->data by a huge offset, pointing outside skb->head area.
Allow debug builds to splat when we try to pull/push more than INT_MAX bytes.
After this, the syzkaller reproducer yields a more precise splat before the flow dissector attempts to read off skb->data memory:
WARNING: CPU: 5 PID: 2313 at include/linux/skbuff.h:2653 neigh_connected_output+0x28e/0x400 ip_finish_output2+0xb25/0xed0 iptunnel_xmit+0x4ff/0x870 ipgre_xmit+0x78e/0xbb0
{
"affected": [],
"aliases": [
"CVE-2024-35941"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-05-19T11:15:49Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: skbuff: add overflow debug check to pull/push helpers\n\nsyzbot managed to trigger following splat:\nBUG: KASAN: use-after-free in __skb_flow_dissect+0x4a3b/0x5e50\nRead of size 1 at addr ffff888208a4000e by task a.out/2313\n[..]\n __skb_flow_dissect+0x4a3b/0x5e50\n __skb_get_hash+0xb4/0x400\n ip_tunnel_xmit+0x77e/0x26f0\n ipip_tunnel_xmit+0x298/0x410\n ..\n\nAnalysis shows that the skb has a valid -\u003ehead, but bogus -\u003edata\npointer.\n\nskb-\u003edata gets its bogus value via the neigh layer, which does:\n\n1556 __skb_pull(skb, skb_network_offset(skb));\n\n... and the skb was already dodgy at this point:\n\nskb_network_offset(skb) returns a negative value due to an\nearlier overflow of skb-\u003enetwork_header (u16). __skb_pull thus\n\"adjusts\" skb-\u003edata by a huge offset, pointing outside skb-\u003ehead\narea.\n\nAllow debug builds to splat when we try to pull/push more than\nINT_MAX bytes.\n\nAfter this, the syzkaller reproducer yields a more precise splat\nbefore the flow dissector attempts to read off skb-\u003edata memory:\n\nWARNING: CPU: 5 PID: 2313 at include/linux/skbuff.h:2653 neigh_connected_output+0x28e/0x400\n ip_finish_output2+0xb25/0xed0\n iptunnel_xmit+0x4ff/0x870\n ipgre_xmit+0x78e/0xbb0",
"id": "GHSA-f3c9-5q5h-57m3",
"modified": "2024-05-19T12:30:39Z",
"published": "2024-05-19T12:30:39Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-35941"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1b2b26595bb09febf14c5444c873ac4ec90a5a77"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/219eee9c0d16f1b754a8b85275854ab17df0850a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8af60bb2b215f478b886f1d6d302fefa7f0b917d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/fff05b2b004d9a8a2416d08647f3dc9068e357c8"
}
],
"schema_version": "1.4.0",
"severity": []
}
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