ext4: check for allocation block validity with block group locked

commit 8d5a803c6a6ce4ec258e31f76059ea5153ba46ef upstream.

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>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index a6a13ad3d5373bb5c5e5c3d795798089331bd855..5cd0c5524daf6ccf4093ca56748c10f55523f020 100644 (file)
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -377,6 +377,8 @@ static void ext4_validate_block_bitmap(struct super_block *sb,
                return;
 
        ext4_lock_group(sb, block_group);
+       if (buffer_verified(bh))
+               goto verified;
        blk = ext4_valid_block_bitmap(sb, desc, block_group, bh);
        if (unlikely(blk != 0)) {
                ext4_unlock_group(sb, block_group);
@@ -399,6 +401,7 @@ static void ext4_validate_block_bitmap(struct super_block *sb,
                return;
        }
        set_buffer_verified(bh);
+verified:
        ext4_unlock_group(sb, block_group);
 }
 

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 3830dc1f895777b09e7df95d30f6cf78aaa244c1..18479ebf2ce1d75d992254276855f4ea8e8d8629 100644 (file)
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -166,6 +166,8 @@ ext4_read_inode_bitmap(struct super_block *sb, ext4_group_t block_group)
 
 verify:
        ext4_lock_group(sb, block_group);
+       if (buffer_verified(bh))
+               goto verified;
        if (!buffer_verified(bh) &&
            !ext4_inode_bitmap_csum_verify(sb, block_group, desc, bh,
                                           EXT4_INODES_PER_GROUP(sb) / 8)) {
@@ -183,8 +185,9 @@ verify:
                set_bit(EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT, &grp->bb_state);
                return NULL;
        }
-       ext4_unlock_group(sb, block_group);
        set_buffer_verified(bh);
+verified:
+       ext4_unlock_group(sb, block_group);
        return bh;
 }