CVE-2024-27036 cifs: Fix writeback data corruption
A logic error in Linux kernel CIFS writeback causes data corruption when copying files to shares with specific wsize settings.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2024-27036?
CVE-2024-27036 is a high-severity vulnerability in Linux kernel, published on 1 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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).
Weakness: CWE-787
Which versions are affected by CVE-2024-27036?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-27036?
Apply the vendor's patch.
Is CVE-2024-27036 being exploited?
There is no known exploitation of CVE-2024-27036 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2024-27036, DEBIAN-CVE-2024-27036, GHSA-vc8w-q4f6-f3fg, UBUNTU-CVE-2024-27036.