ext4: use more strict checks for inodes_per_block on mount

BugLink: http://bugs.launchpad.net/bugs/1654602

commit cd6bb35b upstream.

Centralize the checks for inodes_per_block and be more strict to make
sure the inodes_per_block_group can't end up being zero.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

fs/ext4/super.c

@@ -3531,12 +3531,16 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 
 	sbi->s_blocks_per_group = le32_to_cpu(es->s_blocks_per_group);
 	sbi->s_inodes_per_group = le32_to_cpu(es->s_inodes_per_group);
-	if (EXT4_INODE_SIZE(sb) == 0 || EXT4_INODES_PER_GROUP(sb) == 0)
-		goto cantfind_ext4;
 
 	sbi->s_inodes_per_block = blocksize / EXT4_INODE_SIZE(sb);
 	if (sbi->s_inodes_per_block == 0)
 		goto cantfind_ext4;
+	if (sbi->s_inodes_per_group < sbi->s_inodes_per_block ||
+	    sbi->s_inodes_per_group > blocksize * 8) {
+		ext4_msg(sb, KERN_ERR, "invalid inodes per group: %lu\n",
+			 sbi->s_blocks_per_group);
+		goto failed_mount;
+	}
 	sbi->s_itb_per_group = sbi->s_inodes_per_group /
 					sbi->s_inodes_per_block;
 	sbi->s_desc_per_block = blocksize / EXT4_DESC_SIZE(sb);
@@ -3619,13 +3623,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	}
 	sbi->s_cluster_ratio = clustersize / blocksize;
 
-	if (sbi->s_inodes_per_group > blocksize * 8) {
-		ext4_msg(sb, KERN_ERR,
-		       "#inodes per group too big: %lu",
-		       sbi->s_inodes_per_group);
-		goto failed_mount;
-	}
-
 	/* Do we have standard group size of clustersize * 8 blocks ? */
 	if (sbi->s_blocks_per_group == clustersize << 3)
 		set_opt2(sb, STD_GROUP_SIZE);