--- /dev/null
+From 22be37acce25d66ecf6403fc8f44df9c5ded2372 Mon Sep 17 00:00:00 2001
+From: Lukas Czerner <lczerner@redhat.com>
+Date: Tue, 24 Apr 2018 11:31:44 -0400
+Subject: ext4: fix bitmap position validation
+
+From: Lukas Czerner <lczerner@redhat.com>
+
+commit 22be37acce25d66ecf6403fc8f44df9c5ded2372 upstream.
+
+Currently in ext4_valid_block_bitmap() we expect the bitmap to be
+positioned anywhere between 0 and s_blocksize clusters, but that's
+wrong because the bitmap can be placed anywhere in the block group. This
+causes false positives when validating bitmaps on perfectly valid file
+system layouts. Fix it by checking whether the bitmap is within the group
+boundary.
+
+The problem can be reproduced using the following
+
+mkfs -t ext3 -E stride=256 /dev/vdb1
+mount /dev/vdb1 /mnt/test
+cd /mnt/test
+wget https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.16.3.tar.xz
+tar xf linux-4.16.3.tar.xz
+
+This will result in the warnings in the logs
+
+EXT4-fs error (device vdb1): ext4_validate_block_bitmap:399: comm tar: bg 84: block 2774529: invalid block bitmap
+
+[ Changed slightly for clarity and to not drop a overflow test -- TYT ]
+
+Signed-off-by: Lukas Czerner <lczerner@redhat.com>
+Signed-off-by: Theodore Ts'o <tytso@mit.edu>
+Reported-by: Ilya Dryomov <idryomov@gmail.com>
+Fixes: 7dac4a1726a9 ("ext4: add validity checks for bitmap block numbers")
+Cc: stable@vger.kernel.org
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ fs/ext4/balloc.c | 9 +++++----
+ 1 file changed, 5 insertions(+), 4 deletions(-)
+
+--- a/fs/ext4/balloc.c
++++ b/fs/ext4/balloc.c
+@@ -321,6 +321,7 @@ static ext4_fsblk_t ext4_valid_block_bit
+ struct ext4_sb_info *sbi = EXT4_SB(sb);
+ ext4_grpblk_t offset;
+ ext4_grpblk_t next_zero_bit;
++ ext4_grpblk_t max_bit = EXT4_CLUSTERS_PER_GROUP(sb);
+ ext4_fsblk_t blk;
+ ext4_fsblk_t group_first_block;
+
+@@ -338,7 +339,7 @@ static ext4_fsblk_t ext4_valid_block_bit
+ /* check whether block bitmap block number is set */
+ blk = ext4_block_bitmap(sb, desc);
+ offset = blk - group_first_block;
+- if (offset < 0 || EXT4_B2C(sbi, offset) >= sb->s_blocksize ||
++ if (offset < 0 || EXT4_B2C(sbi, offset) >= max_bit ||
+ !ext4_test_bit(EXT4_B2C(sbi, offset), bh->b_data))
+ /* bad block bitmap */
+ return blk;
+@@ -346,7 +347,7 @@ static ext4_fsblk_t ext4_valid_block_bit
+ /* check whether the inode bitmap block number is set */
+ blk = ext4_inode_bitmap(sb, desc);
+ offset = blk - group_first_block;
+- if (offset < 0 || EXT4_B2C(sbi, offset) >= sb->s_blocksize ||
++ if (offset < 0 || EXT4_B2C(sbi, offset) >= max_bit ||
+ !ext4_test_bit(EXT4_B2C(sbi, offset), bh->b_data))
+ /* bad block bitmap */
+ return blk;
+@@ -354,8 +355,8 @@ static ext4_fsblk_t ext4_valid_block_bit
+ /* check whether the inode table block number is set */
+ blk = ext4_inode_table(sb, desc);
+ offset = blk - group_first_block;
+- if (offset < 0 || EXT4_B2C(sbi, offset) >= sb->s_blocksize ||
+- EXT4_B2C(sbi, offset + sbi->s_itb_per_group) >= sb->s_blocksize)
++ if (offset < 0 || EXT4_B2C(sbi, offset) >= max_bit ||
++ EXT4_B2C(sbi, offset + sbi->s_itb_per_group) >= max_bit)
+ return blk;
+ next_zero_bit = ext4_find_next_zero_bit(bh->b_data,
+ EXT4_B2C(sbi, offset + EXT4_SB(sb)->s_itb_per_group),