e2fsck: write dir blocks after new inode when reconstructing root/lost+found

If we trash the root directory block, e2fsck will find inode 11 (the
old lost+found) and try to attach it to l+f.  The lost+found checker
also fails to find l+f and tries to add one to the root dir.  The root
dir is not found but is recreated with incorrect checksums, so linking
in the l+f dir fails and the l+f '..' entry isn't set.  Since both
dirs now fail checksum verification, they're both referred to rehash
to have that fixed, but because l+f doesn't have a '..' entry, rehash
crashes because l+f has < 2 entries.

On a checksumming filesystem, the routines in e2fsck that recreate
/lost+found and / must write the new directory block *after* the inode
has been written to disk because the checksum depends on i_generation.
Add a regression test while we're at it.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

e2fsck/pass3.c

@@ -204,28 +204,6 @@ skip_new_block:
 	ext2fs_mark_block_bitmap2(fs->block_map, blk);
 	ext2fs_mark_bb_dirty(fs);
 
-	/*
-	 * Now let's create the actual data block for the inode
-	 */
-	pctx.errcode = ext2fs_new_dir_block(fs, EXT2_ROOT_INO, EXT2_ROOT_INO,
-					    &block);
-	if (pctx.errcode) {
-		pctx.str = "ext2fs_new_dir_block";
-		fix_problem(ctx, PR_3_CREATE_ROOT_ERROR, &pctx);
-		ctx->flags |= E2F_FLAG_ABORT;
-		return;
-	}
-
-	pctx.errcode = ext2fs_write_dir_block4(fs, blk, block, 0,
-					       EXT2_ROOT_INO);
-	if (pctx.errcode) {
-		pctx.str = "ext2fs_write_dir_block4";
-		fix_problem(ctx, PR_3_CREATE_ROOT_ERROR, &pctx);
-		ctx->flags |= E2F_FLAG_ABORT;
-		return;
-	}
-	ext2fs_free_mem(&block);
-
 	/*
 	 * Set up the inode structure
 	 */
@@ -248,6 +226,30 @@ skip_new_block:
 		return;
 	}
 
+	/*
+	 * Now let's create the actual data block for the inode.
+	 * Due to metadata_csum, we must write the dir blocks AFTER
+	 * the inode has been written to disk!
+	 */
+	pctx.errcode = ext2fs_new_dir_block(fs, EXT2_ROOT_INO, EXT2_ROOT_INO,
+					    &block);
+	if (pctx.errcode) {
+		pctx.str = "ext2fs_new_dir_block";
+		fix_problem(ctx, PR_3_CREATE_ROOT_ERROR, &pctx);
+		ctx->flags |= E2F_FLAG_ABORT;
+		return;
+	}
+
+	pctx.errcode = ext2fs_write_dir_block4(fs, blk, block, 0,
+					       EXT2_ROOT_INO);
+	ext2fs_free_mem(&block);
+	if (pctx.errcode) {
+		pctx.str = "ext2fs_write_dir_block4";
+		fix_problem(ctx, PR_3_CREATE_ROOT_ERROR, &pctx);
+		ctx->flags |= E2F_FLAG_ABORT;
+		return;
+	}
+
 	/*
 	 * Miscellaneous bookkeeping...
 	 */
@@ -471,24 +473,6 @@ skip_new_block:
 	ext2fs_mark_inode_bitmap2(ctx->inode_dir_map, ino);
 	ext2fs_inode_alloc_stats2(fs, ino, +1, 1);
 
-	/*
-	 * Now let's create the actual data block for the inode
-	 */
-	retval = ext2fs_new_dir_block(fs, ino, EXT2_ROOT_INO, &block);
-	if (retval) {
-		pctx.errcode = retval;
-		fix_problem(ctx, PR_3_ERR_LPF_NEW_DIR_BLOCK, &pctx);
-		return 0;
-	}
-
-	retval = ext2fs_write_dir_block4(fs, blk, block, 0, ino);
-	ext2fs_free_mem(&block);
-	if (retval) {
-		pctx.errcode = retval;
-		fix_problem(ctx, PR_3_ERR_LPF_WRITE_BLOCK, &pctx);
-		return 0;
-	}
-
 	/*
 	 * Set up the inode structure
 	 */
@@ -509,6 +493,27 @@ skip_new_block:
 		fix_problem(ctx, PR_3_CREATE_LPF_ERROR, &pctx);
 		return 0;
 	}
+
+	/*
+	 * Now let's create the actual data block for the inode.
+	 * Due to metadata_csum, the directory block MUST be written
+	 * after the inode is written to disk!
+	 */
+	retval = ext2fs_new_dir_block(fs, ino, EXT2_ROOT_INO, &block);
+	if (retval) {
+		pctx.errcode = retval;
+		fix_problem(ctx, PR_3_ERR_LPF_NEW_DIR_BLOCK, &pctx);
+		return 0;
+	}
+
+	retval = ext2fs_write_dir_block4(fs, blk, block, 0, ino);
+	ext2fs_free_mem(&block);
+	if (retval) {
+		pctx.errcode = retval;
+		fix_problem(ctx, PR_3_ERR_LPF_WRITE_BLOCK, &pctx);
+		return 0;
+	}
+
 	/*
 	 * Finally, create the directory link
 	 */

tests/f_rebuild_csum_rootdir/expect.1

@@ -0,0 +1,311 @@
+Pass 1: Checking inodes, blocks, and sizes
+Pass 2: Checking directory structure
+Directory inode 2, block #0, offset 0: directory has no checksum.
+Fix? yes
+
+Directory inode 2, block #0, offset 0: directory corrupted
+Salvage? yes
+
+Missing '.' in directory inode 2.
+Fix? yes
+
+Setting filetype for entry '.' in ??? (2) to 2.
+Missing '..' in directory inode 2.
+Fix? yes
+
+Setting filetype for entry '..' in ??? (2) to 2.
+Pass 3: Checking directory connectivity
+'..' in / (2) is <The NULL inode> (0), should be / (2).
+Fix? yes
+
+Unconnected directory inode 11 (/???)
+Connect to /lost+found? yes
+
+/lost+found not found.  Create? yes
+
+Pass 3A: Optimizing directories
+Pass 4: Checking reference counts
+Inode 11 ref count is 3, should be 2.  Fix? yes
+
+Unattached inode 12
+Connect to /lost+found? yes
+
+Inode 12 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 13
+Connect to /lost+found? yes
+
+Inode 13 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 14
+Connect to /lost+found? yes
+
+Inode 14 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 15
+Connect to /lost+found? yes
+
+Inode 15 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 16
+Connect to /lost+found? yes
+
+Inode 16 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 17
+Connect to /lost+found? yes
+
+Inode 17 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 18
+Connect to /lost+found? yes
+
+Inode 18 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 19
+Connect to /lost+found? yes
+
+Inode 19 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 20
+Connect to /lost+found? yes
+
+Inode 20 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 21
+Connect to /lost+found? yes
+
+Inode 21 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 22
+Connect to /lost+found? yes
+
+Inode 22 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 23
+Connect to /lost+found? yes
+
+Inode 23 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 24
+Connect to /lost+found? yes
+
+Inode 24 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 25
+Connect to /lost+found? yes
+
+Inode 25 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 26
+Connect to /lost+found? yes
+
+Inode 26 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 27
+Connect to /lost+found? yes
+
+Inode 27 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 28
+Connect to /lost+found? yes
+
+Inode 28 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 29
+Connect to /lost+found? yes
+
+Inode 29 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 30
+Connect to /lost+found? yes
+
+Inode 30 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 31
+Connect to /lost+found? yes
+
+Inode 31 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 32
+Connect to /lost+found? yes
+
+Inode 32 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 33
+Connect to /lost+found? yes
+
+Inode 33 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 34
+Connect to /lost+found? yes
+
+Inode 34 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 35
+Connect to /lost+found? yes
+
+Inode 35 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 36
+Connect to /lost+found? yes
+
+Inode 36 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 37
+Connect to /lost+found? yes
+
+Inode 37 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 38
+Connect to /lost+found? yes
+
+Inode 38 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 39
+Connect to /lost+found? yes
+
+Inode 39 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 40
+Connect to /lost+found? yes
+
+Inode 40 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 41
+Connect to /lost+found? yes
+
+Inode 41 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 42
+Connect to /lost+found? yes
+
+Inode 42 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 43
+Connect to /lost+found? yes
+
+Inode 43 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 44
+Connect to /lost+found? yes
+
+Inode 44 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 45
+Connect to /lost+found? yes
+
+Inode 45 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 46
+Connect to /lost+found? yes
+
+Inode 46 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 47
+Connect to /lost+found? yes
+
+Inode 47 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 48
+Connect to /lost+found? yes
+
+Inode 48 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 49
+Connect to /lost+found? yes
+
+Inode 49 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 50
+Connect to /lost+found? yes
+
+Inode 50 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 51
+Connect to /lost+found? yes
+
+Inode 51 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 52
+Connect to /lost+found? yes
+
+Inode 52 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 53
+Connect to /lost+found? yes
+
+Inode 53 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 54
+Connect to /lost+found? yes
+
+Inode 54 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 55
+Connect to /lost+found? yes
+
+Inode 55 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 56
+Connect to /lost+found? yes
+
+Inode 56 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 57
+Connect to /lost+found? yes
+
+Inode 57 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 58
+Connect to /lost+found? yes
+
+Inode 58 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 59
+Connect to /lost+found? yes
+
+Inode 59 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 60
+Connect to /lost+found? yes
+
+Inode 60 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 61
+Connect to /lost+found? yes
+
+Inode 61 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 62
+Connect to /lost+found? yes
+
+Inode 62 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 63
+Connect to /lost+found? yes
+
+Inode 63 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 64
+Connect to /lost+found? yes
+
+Inode 64 ref count is 2, should be 1.  Fix? yes
+
+Unattached zero-length inode 65.  Clear? yes
+
+Unattached inode 66
+Connect to /lost+found? yes
+
+Inode 66 ref count is 2, should be 1.  Fix? yes
+
+Unattached inode 67
+Connect to /lost+found? yes
+
+Inode 67 ref count is 2, should be 1.  Fix? yes
+
+Pass 5: Checking group summary information
+
+test_filesys: ***** FILE SYSTEM WAS MODIFIED *****
+test_filesys: 67/512 files (1.5% non-contiguous), 1127/2048 blocks
+Exit status is 1

tests/f_rebuild_csum_rootdir/expect.2

@@ -0,0 +1,7 @@
+Pass 1: Checking inodes, blocks, and sizes
+Pass 2: Checking directory structure
+Pass 3: Checking directory connectivity
+Pass 4: Checking reference counts
+Pass 5: Checking group summary information
+test_filesys: 67/512 files (1.5% non-contiguous), 1127/2048 blocks
+Exit status is 0

tests/f_rebuild_csum_rootdir/name

@@ -0,0 +1 @@
+force fsck to rebuild a corrupted rootdir w/ metadata_csum