ext4: check for allocation block validity with block group locked

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@mit.edu>
Cc: stable@kernel.org

2 files changed, 6 insertions, 0 deletions

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index e68cefe08261..aa52d87985aa 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -368,6 +368,8 @@ 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);
@@ -386,6 +388,7 @@ 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 fb83750c1a14..e9d8e2667ab5 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -90,6 +90,8 @@ 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)) {
@@ -101,6 +103,7 @@ 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;
 }