[Bug 2098641] Re: FAT filesystem probing fails if a file's timestamp exceeds 2038

[Mate Kukri]

Does not seem to affect kernel.

** No longer affects: linux-bluefield (Ubuntu)

** No longer affects: linux-bluefield (Ubuntu Focal)

** No longer affects: linux-bluefield (Ubuntu Jammy)

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https://bugs.launchpad.net/bugs/2098641

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

Status in grub2 package in Ubuntu:
  Won't Fix
Status in grub2-unsigned package in Ubuntu:
  Fix Released
Status in grub2 source package in Focal:
  Won't Fix
Status in grub2-unsigned source package in Focal:
  Fix Released
Status in grub2 source package in Jammy:
  Won't Fix
Status in grub2-unsigned source package in Jammy:
  Fix Released

Bug description:
  [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 at 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.

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