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

PATCH In review Benjamin Gilbert 2 participants 2 messages Aug 2, 2018 – Aug 7, 2018

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Stable branch ext4 file system
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Benjamin Gilbert

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PATCH 1/1 ext4: fix false negatives *and* false positives in ext4_check_descriptors()

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 <[email protected]>
Cc [email protected]
Signed-off-by Benjamin Gilbert <[email protected]>
---
 fs/ext4/super.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
fs/ext4/super.c +2 -2
index fc32a67a7a19..a500f55d421a 100644
@@ -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);
Signature · 1 line
2.17.1
#1 lore raw
Quoted 2 lines · Benjamin Gilbert

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

Now applied, thanks.

greg k-h