[PATCH] fat: Allow out-of-range FAT modification timestamps

[Tomasz Kramkowski]

20def1a3c introduced support for file modification times to allow
comparison of file ages on EFI systems. This patch used
grub_datetime2unixtime which uses a 32 bit unix timestamp and as a
result did not allow the full range of times that FAT timestamps do.

In some situations a file with a timestamp of 1970-01-01 gets
transferred to a FAT partition, the timestamp ends up as 2098-01-01
because of FAT's use of the 1980-01-01 DOS epoch and lack of negative
timestamps.

Since 2098 is after 2038, this date cannot fit in a 32 bit timestamp.

Ideally grub should use 64 bit timestamps but I have not investigated
what kind of work would be required to support this.

This fixes bug #60565.

Reported-by: Naïm Favier <n+grub@monade.li>
Tested-by: Naïm Favier <n+grub@monade.li>
Signed-off-by: Tomasz Kramkowski <tk@the-tk.com>
---
 grub-core/fs/fat.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/grub-core/fs/fat.c b/grub-core/fs/fat.c
index dd82e4ee3..34589d7db 100644
--- a/grub-core/fs/fat.c
+++ b/grub-core/fs/fat.c
@@ -1020,16 +1020,17 @@ grub_fat_dir (grub_device_t device, const char *path, 
grub_fs_dir_hook_t hook,
       info.mtimeset = grub_exfat_timestamp (grub_le_to_cpu32 
(ctxt.entry.type_specific.file.m_time),
                                            
ctxt.entry.type_specific.file.m_time_tenth,
                                            &info.mtime);
+      if (info.mtimeset == 0)
+       grub_dprintf("exfat", "invalid modification timestamp for %s\n", path);
 #else
       if (ctxt.dir.attr & GRUB_FAT_ATTR_VOLUME_ID)
        continue;
       info.mtimeset = grub_fat_timestamp (grub_le_to_cpu16 (ctxt.dir.w_time),
                                          grub_le_to_cpu16 (ctxt.dir.w_date),
                                          &info.mtime);
-#endif
       if (info.mtimeset == 0)
-       grub_error (GRUB_ERR_OUT_OF_RANGE,
-                   "invalid modification timestamp for %s", path);
+       grub_dprintf("fat", "invalid modification timestamp for %s\n", path);
+#endif
 
       if (hook (ctxt.filename, &info, hook_data))
        break;
-- 
2.32.0