resize2fs: Fix data corruption bug when growing an ext4 filesystem off-line

When allocating a new set of block group metadata as part of growing
the filesystem, the resize2fs code assumes that the bitmap and inode
table blocks are in their own block group; an assumption which is
changed by the flex_bg feature.  This commit works around the problem
by temporarily turning off flex_bg while allocating the new block
group metadata, to avoid potentially overwriting previously allocated
data blocks.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/resize/resize2fs.c b/resize/resize2fs.c
index 1173da1f0d9057ed97aea5e0b71ef89150c057bb..0c1549bfdd9127200db685df50c38c3f88340f40 100644 (file)
--- a/resize/resize2fs.c
+++ b/resize/resize2fs.c
@@ -746,6 +746,7 @@ static errcode_t blocks_to_move(ext2_resize_t rfs)
        errcode_t       retval;
        ext2_filsys     fs, old_fs;
        ext2fs_block_bitmap     meta_bmap;
+       __u32           save_incompat_flag;
 
        fs = rfs->new_fs;
        old_fs = rfs->old_fs;
@@ -890,9 +891,29 @@ static errcode_t blocks_to_move(ext2_resize_t rfs)
 
                /*
                 * Allocate the missing data structures
+                *
+                * XXX We have a problem with FLEX_BG and off-line
+                * resizing where we are growing the size of the
+                * filesystem.  ext2fs_allocate_group_table() will try
+                * to reserve the inode table in the desired flex_bg
+                * location.  However, passing rfs->reserve_blocks
+                * doesn't work since it only has reserved the blocks
+                * that will be used in the new block group -- and
+                * with flex_bg, we can and will allocate the tables
+                * outside of the block group.  And we can't pass in
+                * the fs->block_map because it doesn't handle
+                * overlapping inode table movements right.  So for
+                * now, we temporarily disable flex_bg to force
+                * ext2fs_allocate_group_tables() to allocate the bg
+                * metadata in side the block group, and the restore
+                * it afterwards.  Ugly, until we can fix this up
+                * right later.
                 */
+               save_incompat_flag = fs->super->s_feature_incompat;
+               fs->super->s_feature_incompat &= ~EXT4_FEATURE_INCOMPAT_FLEX_BG;
                retval = ext2fs_allocate_group_table(fs, i,
                                                     rfs->reserve_blocks);
+               fs->super->s_feature_incompat = save_incompat_flag;
                if (retval)
                        goto errout;