fs: fat: Initialize filesystem timestamp ranges

Fill in the appropriate limits to avoid inconsistencies
in the vfs cached inode times when timestamps are
outside the permitted range.

Some FAT variants indicate that the years after 2099 are not supported.
Since commit 7decd1cb ("fat: Fix and cleanup timestamp conversion")
we support the full range of years that can be represented, up to 2107.
Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Acked-by: Jeff Layton <jlayton@kernel.org>
Cc: hirofumi@mail.parknet.co.jp

fs/fat/inode.c

@@ -31,6 +31,11 @@
 
 #define KB_IN_SECTORS 2
 
+/* DOS dates from 1980/1/1 through 2107/12/31 */
+#define FAT_DATE_MIN (0<<9 | 1<<5 | 1)
+#define FAT_DATE_MAX (127<<9 | 12<<5 | 31)
+#define FAT_TIME_MAX (23<<11 | 59<<5 | 29)
+
 /*
  * A deserialized copy of the on-disk structure laid out in struct
  * fat_boot_sector.
@@ -1605,6 +1610,7 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
 	int debug;
 	long error;
 	char buf[50];
+	struct timespec64 ts;
 
 	/*
 	 * GFP_KERNEL is ok here, because while we do hold the
@@ -1698,6 +1704,12 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
 	sbi->free_clus_valid = 0;
 	sbi->prev_free = FAT_START_ENT;
 	sb->s_maxbytes = 0xffffffff;
+	fat_time_fat2unix(sbi, &ts, 0, cpu_to_le16(FAT_DATE_MIN), 0);
+	sb->s_time_min = ts.tv_sec;
+
+	fat_time_fat2unix(sbi, &ts, cpu_to_le16(FAT_TIME_MAX),
+			  cpu_to_le16(FAT_DATE_MAX), 0);
+	sb->s_time_max = ts.tv_sec;
 
 	if (!sbi->fat_length && bpb.fat32_length) {
 		struct fat_boot_fsinfo *fsinfo;