CVE-2024-27036: linux kernel Memory Corruption — Fix

Description

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).

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CVSS v3.1 Score

7.8

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Weakness Type (CWE)

CWE-787 Out-of-bounds Write

Affected Products

Vendor	Product	Versions
linux	linux_kernel	6.3 — 6.6.23
linux	linux_kernel	6.7 — 6.7.11
linux	linux_kernel	6.8 — 6.8.2

References

Advisories & Patches

https://git.kernel.org/stable/c/65f2ced695982ccd516196d0a9447d85dbe2eed5 https://git.kernel.org/stable/c/844b4e132f57f1333dc79feaa035075a096762e4 https://git.kernel.org/stable/c/e45deec35bf7f1f4f992a707b2d04a8c162f2240 https://git.kernel.org/stable/c/f3dc1bdb6b0b0693562c7c54a6c28bafa608ba3c https://git.kernel.org/stable/c/65f2ced695982ccd516196d0a9447d85dbe2eed5 https://git.kernel.org/stable/c/844b4e132f57f1333dc79feaa035075a096762e4 https://git.kernel.org/stable/c/e45deec35bf7f1f4f992a707b2d04a8c162f2240 https://git.kernel.org/stable/c/f3dc1bdb6b0b0693562c7c54a6c28bafa608ba3c

Frequently Asked Questions

What is CVE-2024-27036? +

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). It has a CVSS v3.1 base score of 7.8 (HIGH).

How severe is CVE-2024-27036? +

CVE-2024-27036 has a CVSS v3.1 score of 7.8 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

What products are affected by CVE-2024-27036? +

CVE-2024-27036 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2024-27036? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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