exfat: fix s_maxbytes

With fallocate support, xfstest unit generic/213 fails with

   QA output created by 213
   We should get: fallocate: No space left on device
   Strangely, xfs_io sometimes says "Success" when something went wrong
  -fallocate: No space left on device
  +fallocate: File too large

because sb->s_maxbytes is set to the volume size.

To be in line with other non-extent-based filesystems, set to max volume
size possible with the cluster size of the volume.

Signed-off-by: David Timber <dxdt@dev.snart.me>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

Author: dxdxdt

fs/exfat/exfat_raw.h

@@ -25,6 +25,7 @@
 #define EXFAT_FIRST_CLUSTER	2
 #define EXFAT_DATA_CLUSTER_COUNT(sbi)	\
 	((sbi)->num_clusters - EXFAT_RESERVED_CLUSTERS)
+#define EXFAT_MAX_NUM_CLUSTER		(0xFFFFFFF5)
 
 /* AllocationPossible and NoFatChain field in GeneralSecondaryFlags Field */
 #define ALLOC_POSSIBLE		0x01

fs/exfat/file.c

@@ -34,6 +34,7 @@ static int exfat_cont_expand(struct inode *inode, loff_t size)
 		return ret;
 
 	num_clusters = EXFAT_B_TO_CLU(exfat_ondisk_size(inode), sbi);
+	/* integer overflow is already checked in inode_newsize_ok(). */
 	new_num_clusters = EXFAT_B_TO_CLU_ROUND_UP(size, sbi);
 
 	if (new_num_clusters == num_clusters)

fs/exfat/super.c

@@ -531,9 +531,14 @@ static int exfat_read_boot_sector(struct super_block *sb)
 	if (sbi->vol_flags & MEDIA_FAILURE)
 		exfat_warn(sb, "Medium has reported failures. Some data may be lost.");
 
-	/* exFAT file size is limited by a disk volume size */
-	sb->s_maxbytes = (u64)(sbi->num_clusters - EXFAT_RESERVED_CLUSTERS) <<
-		sbi->cluster_size_bits;
+	/*
+	 * Set to the max possible volume size for this volume's cluster size so
+	 * that any integer overflow from bytes to cluster size conversion is
+	 * checked in inode_newsize_ok(). Clamped to MAX_LFS_FILESIZE for 32-bit
+	 * machines.
+	 */
+	sb->s_maxbytes = min(MAX_LFS_FILESIZE,
+			     EXFAT_CLU_TO_B((loff_t)EXFAT_MAX_NUM_CLUSTER, sbi));
 
 	/* check logical sector size */
 	if (exfat_calibrate_blocksize(sb, 1 << p_boot->sect_size_bits))