ext4: use atomic64_t for the per-flexbg free_clusters count

A user who was using a 8TB+ file system and with a very large flexbg
size (> 65536) could cause the atomic_t used in the struct flex_groups
to overflow. This was detected by PaX security patchset:

http://forums.grsecurity.net/viewtopic.php?f=3&t=3289&p=12551#p12551

This bug was introduced in commit 9f24e4208f7e, so it's been around
since 2.6.30. :-(

Fix this by using an atomic64_t for struct orlav_stats's
free_clusters.

Signed-off-by: "Theodore Ts'o" <[e-mail]>
Reviewed-by: Lukas Czerner <[e-mail]>
Cc: [e-mail]

fs/ext4/ext4.h

···
  */
 
 struct flex_groups {
-	atomic_t free_inodes;
-	atomic_t free_clusters;
-	atomic_t used_dirs;
+	atomic64_t	free_clusters;
+	atomic_t	free_inodes;
+	atomic_t	used_dirs;
 };
 
 #define EXT4_BG_INODE_UNINIT	0x0001 /* Inode table/bitmap not in use */

fs/ext4/ialloc.c

···
 }
 
 struct orlov_stats {
+	__u64 free_clusters;
 	__u32 free_inodes;
-	__u32 free_clusters;
 	__u32 used_dirs;
 };
 
···
 
 	if (flex_size > 1) {
 		stats->free_inodes = atomic_read(&flex_group[g].free_inodes);
-		stats->free_clusters = atomic_read(&flex_group[g].free_clusters);
+		stats->free_clusters = atomic64_read(&flex_group[g].free_clusters);
 		stats->used_dirs = atomic_read(&flex_group[g].used_dirs);
 		return;
 	}

fs/ext4/mballoc.c

···
 	if (sbi->s_log_groups_per_flex) {
 		ext4_group_t flex_group = ext4_flex_group(sbi,
 							  ac->ac_b_ex.fe_group);
-		atomic_sub(ac->ac_b_ex.fe_len,
-			   &sbi->s_flex_groups[flex_group].free_clusters);
+		atomic64_sub(ac->ac_b_ex.fe_len,
+			     &sbi->s_flex_groups[flex_group].free_clusters);
 	}
 
 	err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
···
 
 	if (sbi->s_log_groups_per_flex) {
 		ext4_group_t flex_group = ext4_flex_group(sbi, block_group);
-		atomic_add(count_clusters,
-			   &sbi->s_flex_groups[flex_group].free_clusters);
+		atomic64_add(count_clusters,
+			     &sbi->s_flex_groups[flex_group].free_clusters);
 	}
 
 	ext4_mb_unload_buddy(&e4b);
···
 
 	if (sbi->s_log_groups_per_flex) {
 		ext4_group_t flex_group = ext4_flex_group(sbi, block_group);
-		atomic_add(EXT4_NUM_B2C(sbi, blocks_freed),
-			   &sbi->s_flex_groups[flex_group].free_clusters);
+		atomic64_add(EXT4_NUM_B2C(sbi, blocks_freed),
+			     &sbi->s_flex_groups[flex_group].free_clusters);
 	}
 
 	ext4_mb_unload_buddy(&e4b);

fs/ext4/resize.c

···
 	    sbi->s_log_groups_per_flex) {
 		ext4_group_t flex_group;
 		flex_group = ext4_flex_group(sbi, group_data[0].group);
-		atomic_add(EXT4_NUM_B2C(sbi, free_blocks),
-			   &sbi->s_flex_groups[flex_group].free_clusters);
+		atomic64_add(EXT4_NUM_B2C(sbi, free_blocks),
+			     &sbi->s_flex_groups[flex_group].free_clusters);
 		atomic_add(EXT4_INODES_PER_GROUP(sb) * flex_gd->count,
 			   &sbi->s_flex_groups[flex_group].free_inodes);
 	}

fs/ext4/super.c

···
 		flex_group = ext4_flex_group(sbi, i);
 		atomic_add(ext4_free_inodes_count(sb, gdp),
 			   &sbi->s_flex_groups[flex_group].free_inodes);
-		atomic_add(ext4_free_group_clusters(sb, gdp),
-			   &sbi->s_flex_groups[flex_group].free_clusters);
+		atomic64_add(ext4_free_group_clusters(sb, gdp),
+			     &sbi->s_flex_groups[flex_group].free_clusters);
 		atomic_add(ext4_used_dirs_count(sb, gdp),
 			   &sbi->s_flex_groups[flex_group].used_dirs);
 	}