CVE-2024-42305

2024-08-1709:15:10

Linux

web.nvd.nist.gov

linux kernel

ext4 filesystem

vulnerability

resolved

cve-2024-42305

dotdot

dot

symlink

page fault

directory indexing

AI Score

6.6

Confidence

High

EPSS

Percentile

13.7%

JSON

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:
<TASK>
make_indexed_dir+0xdaf/0x13c0 fs/ext4/namei.c:2341
ext4_add_entry+0x222a/0x25d0 fs/ext4/namei.c:2451
ext4_rename fs/ext4/namei.c:3936 [inline]
ext4_rename2+0x26e5/0x4370 fs/ext4/namei.c:4214
[…]

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;
   ---&gt; 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 configurations

Vulners

Node

linuxlinux_kernelRange2.6.19–4.19.320

linuxlinux_kernelRange4.20.0–5.4.282

linuxlinux_kernelRange5.5.0–5.10.224

linuxlinux_kernelRange5.11.0–5.15.165

linuxlinux_kernelRange5.16.0–6.1.103

linuxlinux_kernelRange6.2.0–6.6.44

linuxlinux_kernelRange6.7.0–6.10.3

linuxlinux_kernelRange6.11.0≥

VendorProductVersionCPE
linuxlinux_kernel*cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

Vendor	Product	Version	CPE
linux	linux_kernel	*	cpe:2.3:o:linux:linux_kernel::::::::

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "fs/ext4/namei.c"
    ],
    "versions": [
      {
        "version": "ac27a0ec112a",
        "lessThan": "b80575ffa98b",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "ac27a0ec112a",
        "lessThan": "19e13b4d7f03",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "ac27a0ec112a",
        "lessThan": "42d420517072",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "ac27a0ec112a",
        "lessThan": "8afe06ed3be7",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "ac27a0ec112a",
        "lessThan": "abb411ac9918",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "ac27a0ec112a",
        "lessThan": "9d241b7a39af",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "ac27a0ec112a",
        "lessThan": "cdd345321699",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "ac27a0ec112a",
        "lessThan": "50ea741def58",
        "status": "affected",
        "versionType": "git"
      }
    ]
  },
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "affected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "fs/ext4/namei.c"
    ],
    "versions": [
      {
        "version": "2.6.19",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "2.6.19",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.19.320",
        "lessThanOrEqual": "4.19.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.4.282",
        "lessThanOrEqual": "5.4.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.10.224",
        "lessThanOrEqual": "5.10.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.15.165",
        "lessThanOrEqual": "5.15.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.1.103",
        "lessThanOrEqual": "6.1.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.6.44",
        "lessThanOrEqual": "6.6.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.10.3",
        "lessThanOrEqual": "6.10.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.11",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]