CVE-2024-27036 cifs: Fix writeback data corruption

2024-05-0112:53:46

Linux

github.com

linux

cifs

vulnerability

file corruption

fix

writeback

netfslib

6.8 Medium

AI Score

Confidence

Low

0.0004 Low

EPSS

Percentile

15.5%

JSON

In the Linux kernel, the following vulnerability has been resolved:

cifs: Fix writeback data corruption

cifs writeback doesn’t correctly handle the case where
cifs_extend_writeback() hits a point where it is considering an additional
folio, but this would overrun the wsize - at which point it drops out of
the xarray scanning loop and calls xas_pause(). The problem is that
xas_pause() advances the loop counter - thereby skipping that page.

What needs to happen is for xas_reset() to be called any time we decide we
don’t want to process the page we’re looking at, but rather send the
request we are building and start a new one.

Fix this by copying and adapting the netfslib writepages code as a
temporary measure, with cifs writeback intending to be offloaded to
netfslib in the near future.

This also fixes the issue with the use of filemap_get_folios_tag() causing
retry of a bunch of pages which the extender already dealt with.

This can be tested by creating, say, a 64K file somewhere not on cifs
(otherwise copy-offload may get underfoot), mounting a cifs share with a
wsize of 64000, copying the file to it and then comparing the original file
and the copy:

    dd if=/dev/urandom of=/tmp/64K bs=64k count=1
    mount //192.168.6.1/test /mnt -o user=...,pass=...,wsize=64000
    cp /tmp/64K /mnt/64K
    cmp /tmp/64K /mnt/64K

Without the fix, the cmp fails at position 64000 (or shortly thereafter).

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "fs/smb/client/file.c"
    ],
    "versions": [
      {
        "version": "d08089f649a0",
        "lessThan": "e45deec35bf7",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "d08089f649a0",
        "lessThan": "65f2ced69598",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "d08089f649a0",
        "lessThan": "844b4e132f57",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "d08089f649a0",
        "lessThan": "f3dc1bdb6b0b",
        "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/smb/client/file.c"
    ],
    "versions": [
      {
        "version": "6.3",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "6.3",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.6.23",
        "lessThanOrEqual": "6.6.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.7.11",
        "lessThanOrEqual": "6.7.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.8.2",
        "lessThanOrEqual": "6.8.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.9",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]