[PATCH] ext4: fix false negatives *and* false positives in ext4_check_descriptors()

[PATCH] ext4: fix false negatives *and* false positives in ext4_check_descriptors()

[Benjamin Gilbert]

Fix trivial conflict that caused the original commit to bounce from 4.4,
4.9, and 4.14.

-- >8 --

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>
---
 fs/ext4/super.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index fc32a67a7a19..a500f55d421a 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2301,7 +2301,7 @@ static int ext4_check_descriptors(struct super_block *sb,
 	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;
@@ -4044,13 +4044,13 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 			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);
 
-- 
2.17.1

Re: [PATCH] ext4: fix false negatives *and* false positives in ext4_check_descriptors()

[Greg KH]

On Thu, Aug 02, 2018 at 12:19:00AM -0400, Benjamin Gilbert wrote:
> Fix trivial conflict that caused the original commit to bounce from 4.4,
> 4.9, and 4.14.

Now applied, thanks.

greg k-h