[PATCH 2/2][Cosmic][SRU Bionic] UBUNTU: SAUCE: ext4: check for allocation block validity with block group locked

[dann frazier]

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

BugLink: https://bugs.launchpad.net/bugs/1781709

With commit 044e6e3d74a3: "ext4: don't update checksum of new
initialized bitmaps" the buffer valid bit will get set without
actually setting up the checksum for the allocation bitmap, since the
checksum will get calculated once we actually allocate an inode or
block.

If we are doing this, then we need to (re-)check the verified bit
after we take the block group lock.  Otherwise, we could race with
another process reading and verifying the bitmap, which would then
complain about the checksum being invalid.

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1780137

Signed-off-by: Theodore Ts'o <tytso at mit.edu>
Cc: stable at kernel.org
Signed-off-by: dann frazier <dann.frazier at canonical.com>
---
 fs/ext4/balloc.c | 3 +++
 fs/ext4/ialloc.c | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index e3d4f451d2cf6..57ab866847c02 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -383,6 +383,8 @@ static int ext4_validate_block_bitmap(struct super_block *sb,
 		return -EFSCORRUPTED;
 
 	ext4_lock_group(sb, block_group);
+	if (buffer_verified(bh))
+		goto verified;
 	if (unlikely(!ext4_block_bitmap_csum_verify(sb, block_group,
 			desc, bh))) {
 		ext4_unlock_group(sb, block_group);
@@ -405,6 +407,7 @@ static int ext4_validate_block_bitmap(struct super_block *sb,
 		return -EFSCORRUPTED;
 	}
 	set_buffer_verified(bh);
+verified:
 	ext4_unlock_group(sb, block_group);
 	return 0;
 }
diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 555931386375b..b5e2cc28af470 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -91,6 +91,8 @@ static int ext4_validate_inode_bitmap(struct super_block *sb,
 		return -EFSCORRUPTED;
 
 	ext4_lock_group(sb, block_group);
+	if (buffer_verified(bh))
+		goto verified;
 	blk = ext4_inode_bitmap(sb, desc);
 	if (!ext4_inode_bitmap_csum_verify(sb, block_group, desc, bh,
 					   EXT4_INODES_PER_GROUP(sb) / 8)) {
@@ -108,6 +110,7 @@ static int ext4_validate_inode_bitmap(struct super_block *sb,
 		return -EFSBADCRC;
 	}
 	set_buffer_verified(bh);
+verified:
 	ext4_unlock_group(sb, block_group);
 	return 0;
 }
-- 
2.18.0