FAT filesystem probing fails if a file's timestamp exceeds 2038

[dongzhou]

[Impact]
If any file's timestamp under `/boot/efi` exceeds 2038, the FAT filesystem probe will fail, and the system will drop into the GRUB shell.

[Fix]
There is an upstream patch that fixes this issue:
https://git.savannah.gnu.org/cgit/grub.git/commit/grub-core/fs?id=e43f3d93b28cce852c110c7a8e40d8311bcd8bb1

[Test Plan]
1. Prepare an EFI partition in FAT format.
root@jammy:~# lsblk -f
vda
├─vda1
│ vfat FAT32 C34E-C891 1G 1% /boot/efi
├─vda2
│ ext4 1.0 0cbb726b-e9ac-47bf-8593-9ec43402076f 1.7G 7% /boot
└─vda3
     LVM2_m LVM2 eHoy3y-L7Fk-J4FQ-Fhlw-XXBR-C3xl-gQDAWo
  └─ubuntu--vg-ubuntu--lv
     ext4 1.0 78ec8d75-3ce6-4f09-abba-c6278aec36e7 79.7G 13% /

2. Change the timestamp of a directory under /boot/efi to exceed 2038:
touch -d "2038-02-27" /boot/efi/EFI

3. Reboot, and the system will be entered into the grub shell.

[Where problems could occur]
The patch simply bypasses the error logic when the modification time is zero in FAT.
There should be no regression unless the FAT filesystem is unable to handle such scenarios.

[Chengen Du (chengendu)]

Noble and later versions already include the patch.

[Chengen Du (chengendu)]

Debdiff for grub2 in Jammy

[Chengen Du (chengendu)]

Debdiff for grub2-unsigned in Jammy

[Julian Andres Klode (juliank)]

Mate has cherry-picked the fix into the branch for the pending security update.

[Launchpad Janitor (janitor)]

This bug was fixed in the package grub2-unsigned - 2.06-2ubuntu14.8

---------------
grub2-unsigned (2.06-2ubuntu14.8) jammy; urgency=medium

  * Drop NTFS patches that seem to be causing regressions
  * Source package generated from src:grub2 using make -f ./debian/rules
    generate-grub2-unsigned

 -- Mate Kukri <email address hidden> Mon, 17 Mar 2025 13:34:27 +0000

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "lp2098641-grub2-jammy.debdiff" seems to be a debdiff. The ubuntu-sponsors team has been subscribed to the bug report so that they can review and hopefully sponsor the debdiff. If the attachment isn't a patch, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are member of the ~ubuntu-sponsors, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issue please contact him.]

[Launchpad Janitor (janitor)]

This bug was fixed in the package grub2-unsigned - 2.06-2ubuntu14.8

---------------
grub2-unsigned (2.06-2ubuntu14.8) jammy; urgency=medium

  * Drop NTFS patches that seem to be causing regressions
  * Source package generated from src:grub2 using make -f ./debian/rules
    generate-grub2-unsigned

 -- Mate Kukri <email address hidden> Mon, 17 Mar 2025 13:34:27 +0000