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Subject[PATCH 4.4 08/12] ext4: fix false negatives *and* false positives in ext4_check_descriptors()
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Theodore Ts'o <tytso@mit.edu>

commit 44de022c4382541cebdd6de4465d1f4f465ff1dd upstream.

Ext4_check_descriptors() was getting called before s_gdb_count was
initialized. So for file systems w/o the meta_bg feature, allocation
bitmaps could overlap the block group descriptors and ext4 wouldn't
notice.

For file systems with the meta_bg feature enabled, there was a
fencepost error which would cause the ext4_check_descriptors() to
incorrectly believe that the block allocation bitmap overlaps with the
block group descriptor blocks, and it would reject the mount.

Fix both of these problems.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
Signed-off-by: Benjamin Gilbert <bgilbert@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/ext4/super.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2102,7 +2102,7 @@ static int ext4_check_descriptors(struct
struct ext4_sb_info *sbi = EXT4_SB(sb);
ext4_fsblk_t first_block = le32_to_cpu(sbi->s_es->s_first_data_block);
ext4_fsblk_t last_block;
- ext4_fsblk_t last_bg_block = sb_block + ext4_bg_num_gdb(sb, 0) + 1;
+ ext4_fsblk_t last_bg_block = sb_block + ext4_bg_num_gdb(sb, 0);
ext4_fsblk_t block_bitmap;
ext4_fsblk_t inode_bitmap;
ext4_fsblk_t inode_table;
@@ -3777,13 +3777,13 @@ static int ext4_fill_super(struct super_
goto failed_mount2;
}
}
+ sbi->s_gdb_count = db_count;
if (!ext4_check_descriptors(sb, logical_sb_block, &first_not_zeroed)) {
ext4_msg(sb, KERN_ERR, "group descriptors corrupted!");
ret = -EFSCORRUPTED;
goto failed_mount2;
}

- sbi->s_gdb_count = db_count;
get_random_bytes(&sbi->s_next_generation, sizeof(u32));
spin_lock_init(&sbi->s_next_gen_lock);


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