ext4: fix unjournalled bg descriptor while initializing inode bitmap

The first time that we allocate from an uninitialized inode allocation
bitmap, if the block allocation bitmap is also uninitalized, we need
to get write access to the block group descriptor before we start
modifying the block group descriptor flags and updating the free block
count, etc.  Otherwise, there is the potential of a bad journal
checksum (if journal checksums are enabled), and of the file system
becoming inconsistent if we crash at exactly the wrong time.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index a87455df38bca3e743d603709a208e7da77b61fe..0840bf321cdb59678ef69f17a746845bc0f11314 100644 (file)
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -874,6 +874,13 @@ got:
                goto out;
        }
 
+       BUFFER_TRACE(group_desc_bh, "get_write_access");
+       err = ext4_journal_get_write_access(handle, group_desc_bh);
+       if (err) {
+               ext4_std_error(sb, err);
+               goto out;
+       }
+
        /* We may have to initialize the block bitmap if it isn't already */
        if (ext4_has_group_desc_csum(sb) &&
            gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
@@ -910,13 +917,6 @@ got:
                }
        }
 
-       BUFFER_TRACE(group_desc_bh, "get_write_access");
-       err = ext4_journal_get_write_access(handle, group_desc_bh);
-       if (err) {
-               ext4_std_error(sb, err);
-               goto out;
-       }
-
        /* Update the relevant bg descriptor fields */
        if (ext4_has_group_desc_csum(sb)) {
                int free;