CVE-2024-26821

Published: 17 April 2024

In the Linux kernel, the following vulnerability has been resolved: fs: relax mount_setattr() permission checks When we added mount_setattr() I added additional checks compared to the legacy do_reconfigure_mnt() and do_change_type() helpers used by regular mount(2). If that mount had a parent then verify that the caller and the mount namespace the mount is attached to match and if not make sure that it's an anonymous mount. The real rootfs falls into neither category. It is neither an anoymous mount because it is obviously attached to the initial mount namespace but it also obviously doesn't have a parent mount. So that means legacy mount(2) allows changing mount properties on the real rootfs but mount_setattr(2) blocks this. I never thought much about this but of course someone on this planet of earth changes properties on the real rootfs as can be seen in [1]. Since util-linux finally switched to the new mount api in 2.39 not so long ago it also relies on mount_setattr() and that surfaced this issue when Fedora 39 finally switched to it. Fix this.

Notes

Priority reason:
This issue is loosening restrictions on setting mount attributes on / after it has already been mounted, matching existing behavior.

the issue being addressed here loosens the restrictions on
remounting /, to match prior allowed behavior. The only potential
security impact is if, as part of the boot process, an adjustment of /
attributes was expected to occur that didn't, enabling an unexpected
operation to be able to occur.

Status

References

• https://www.cve.org/CVERecord?id=CVE-2024-26821
• https://git.kernel.org/linus/46f5ab762d048dad224436978315cbc2fa79c630 (6.8-rc5)
• https://git.kernel.org/stable/c/95de4ad173ca0e61034f3145d66917970961c210
• https://git.kernel.org/stable/c/31f71f2d7a081fc6c6bdf06865beedf6db5b0ca4
• https://git.kernel.org/stable/c/2a7a31e1fb9717845d9d5e2a8c6e48848147801e
• https://git.kernel.org/stable/c/46f5ab762d048dad224436978315cbc2fa79c630
• NVD
• Launchpad
• Debian

Bugs

• https://bugzilla.redhat.com/show_bug.cgi?id=2256843