ghsa-46jx-3cg2-9964
Vulnerability from github
In the Linux kernel, the following vulnerability has been resolved:
ext4: check dot and dotdot of dx_root before making dir indexed
Syzbot reports a issue as follows:
BUG: unable to handle page fault for address: ffffed11022e24fe
PGD 23ffee067 P4D 23ffee067 PUD 0
Oops: Oops: 0000 [#1] PREEMPT SMP KASAN PTI
CPU: 0 PID: 5079 Comm: syz-executor306 Not tainted 6.10.0-rc5-g55027e689933 #0
Call Trace:
The immediate cause of this problem is that there is only one valid dentry for the block to be split during do_split, so split==0 results in out of bounds accesses to the map triggering the issue.
do_split
unsigned split
dx_make_map
count = 1
split = count/2 = 0;
continued = hash2 == map[split - 1].hash;
---> map[4294967295]
The maximum length of a filename is 255 and the minimum block size is 1024, so it is always guaranteed that the number of entries is greater than or equal to 2 when do_split() is called.
But syzbot's crafted image has no dot and dotdot in dir, and the dentry distribution in dirblock is as follows:
bus dentry1 hole dentry2 free |xx--|xx-------------|...............|xx-------------|...............| 0 12 (8+248)=256 268 256 524 (8+256)=264 788 236 1024
So when renaming dentry1 increases its name_len length by 1, neither hole nor free is sufficient to hold the new dentry, and make_indexed_dir() is called.
In make_indexed_dir() it is assumed that the first two entries of the dirblock must be dot and dotdot, so bus and dentry1 are left in dx_root because they are treated as dot and dotdot, and only dentry2 is moved to the new leaf block. That's why count is equal to 1.
Therefore add the ext4_check_dx_root() helper function to add more sanity checks to dot and dotdot before starting the conversion to avoid the above issue.
{
"affected": [],
"aliases": [
"CVE-2024-42305"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-08-17T09:15:10Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\next4: check dot and dotdot of dx_root before making dir indexed\n\nSyzbot reports a issue as follows:\n============================================\nBUG: unable to handle page fault for address: ffffed11022e24fe\nPGD 23ffee067 P4D 23ffee067 PUD 0\nOops: Oops: 0000 [#1] PREEMPT SMP KASAN PTI\nCPU: 0 PID: 5079 Comm: syz-executor306 Not tainted 6.10.0-rc5-g55027e689933 #0\nCall Trace:\n \u003cTASK\u003e\n make_indexed_dir+0xdaf/0x13c0 fs/ext4/namei.c:2341\n ext4_add_entry+0x222a/0x25d0 fs/ext4/namei.c:2451\n ext4_rename fs/ext4/namei.c:3936 [inline]\n ext4_rename2+0x26e5/0x4370 fs/ext4/namei.c:4214\n[...]\n============================================\n\nThe immediate cause of this problem is that there is only one valid dentry\nfor the block to be split during do_split, so split==0 results in out of\nbounds accesses to the map triggering the issue.\n\n do_split\n unsigned split\n dx_make_map\n count = 1\n split = count/2 = 0;\n continued = hash2 == map[split - 1].hash;\n ---\u003e map[4294967295]\n\nThe maximum length of a filename is 255 and the minimum block size is 1024,\nso it is always guaranteed that the number of entries is greater than or\nequal to 2 when do_split() is called.\n\nBut syzbot\u0027s crafted image has no dot and dotdot in dir, and the dentry\ndistribution in dirblock is as follows:\n\n bus dentry1 hole dentry2 free\n|xx--|xx-------------|...............|xx-------------|...............|\n0 12 (8+248)=256 268 256 524 (8+256)=264 788 236 1024\n\nSo when renaming dentry1 increases its name_len length by 1, neither hole\nnor free is sufficient to hold the new dentry, and make_indexed_dir() is\ncalled.\n\nIn make_indexed_dir() it is assumed that the first two entries of the\ndirblock must be dot and dotdot, so bus and dentry1 are left in dx_root\nbecause they are treated as dot and dotdot, and only dentry2 is moved\nto the new leaf block. That\u0027s why count is equal to 1.\n\nTherefore add the ext4_check_dx_root() helper function to add more sanity\nchecks to dot and dotdot before starting the conversion to avoid the above\nissue.",
"id": "GHSA-46jx-3cg2-9964",
"modified": "2024-08-19T06:30:53Z",
"published": "2024-08-17T09:30:25Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-42305"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/19e13b4d7f0303186fcc891aba8d0de7c8fdbda8"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/42d420517072028fb0eb852c358056b7717ba5aa"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/50ea741def587a64e08879ce6c6a30131f7111e7"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8afe06ed3be7a874b3cd82ef5f8959aca8d6429a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9d241b7a39af192d1bb422714a458982c7cc67a2"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/abb411ac991810c0bcbe51c2e76d2502bf611b5c"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b80575ffa98b5bb3a5d4d392bfe4c2e03e9557db"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/cdd345321699042ece4a9d2e70754d2397d378c5"
}
],
"schema_version": "1.4.0",
"severity": []
}
- 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.