ext4: ext4_bread usage audit

When ext4_bread() returns NULL and err is set to zero, this means
there is no phyical block mapped to the specified logical block
number.  (Previous to commit 90b0a97323, err was uninitialized in this
case, which caused other problems.)

The directory handling routines use ext4_bread() in many places, the
fact that ext4_bread() now returns NULL with err set to zero could
cause problems since a number of these functions will simply return
the value of err if the result of ext4_bread() was the NULL pointer,
causing the caller of the function to think that the function was
successful.

Since directories should never contain holes, this case can only
happen if the file system is corrupted.  This commit audits all of the
callers of ext4_bread(), and makes sure they do the right thing if a
hole in a directory is found by ext4_bread().

Some ext4_bread() callers did not need any changes either because they
already had its own hole detector paths.

Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/namei.c

@@ -74,6 +74,12 @@ static struct buffer_head *ext4_append(handle_t *handle,
 			bh = NULL;
 		}
 	}
+	if (!bh && !(*err)) {
+		*err = -EIO;
+		ext4_error(inode->i_sb,
+			   "Directory hole detected on inode %lu\n",
+			   inode->i_ino);
+	}
 	return bh;
 }
 
@@ -601,8 +607,11 @@ dx_probe(const struct qstr *d_name, struct inode *dir,
 	u32 hash;
 
 	frame->bh = NULL;
-	if (!(bh = ext4_bread (NULL,dir, 0, 0, err)))
+	if (!(bh = ext4_bread(NULL, dir, 0, 0, err))) {
+		if (*err == 0)
+			*err = ERR_BAD_DX_DIR;
 		goto fail;
+	}
 	root = (struct dx_root *) bh->b_data;
 	if (root->info.hash_version != DX_HASH_TEA &&
 	    root->info.hash_version != DX_HASH_HALF_MD4 &&
@@ -703,8 +712,11 @@ dx_probe(const struct qstr *d_name, struct inode *dir,
 		frame->entries = entries;
 		frame->at = at;
 		if (!indirect--) return frame;
-		if (!(bh = ext4_bread (NULL,dir, dx_get_block(at), 0, err)))
+		if (!(bh = ext4_bread(NULL, dir, dx_get_block(at), 0, err))) {
+			if (!(*err))
+				*err = ERR_BAD_DX_DIR;
 			goto fail2;
+		}
 		at = entries = ((struct dx_node *) bh->b_data)->entries;
 
 		if (!buffer_verified(bh) &&
@@ -814,8 +826,15 @@ static int ext4_htree_next_block(struct inode *dir, __u32 hash,
 	 */
 	while (num_frames--) {
 		if (!(bh = ext4_bread(NULL, dir, dx_get_block(p->at),
-				      0, &err)))
+				      0, &err))) {
+			if (!err) {
+				ext4_error(dir->i_sb,
+					   "Directory hole detected on inode %lu\n",
+					   dir->i_ino);
+				return -EIO;
+			}
 			return err; /* Failure */
+		}
 
 		if (!buffer_verified(bh) &&
 		    !ext4_dx_csum_verify(dir,
@@ -850,8 +869,15 @@ static int htree_dirblock_to_tree(struct file *dir_file,
 
 	dxtrace(printk(KERN_INFO "In htree dirblock_to_tree: block %lu\n",
 							(unsigned long)block));
-	if (!(bh = ext4_bread (NULL, dir, block, 0, &err)))
+	if (!(bh = ext4_bread(NULL, dir, block, 0, &err))) {
+		if (!err) {
+			err = -EIO;
+			ext4_error(dir->i_sb,
+				   "Directory hole detected on inode %lu\n",
+				   dir->i_ino);
+		}
 		return err;
+	}
 
 	if (!buffer_verified(bh) &&
 	    !ext4_dirent_csum_verify(dir, (struct ext4_dir_entry *)bh->b_data))
@@ -1274,8 +1300,15 @@ static struct buffer_head * ext4_dx_find_entry(struct inode *dir, const struct q
 		return NULL;
 	do {
 		block = dx_get_block(frame->at);
-		if (!(bh = ext4_bread(NULL, dir, block, 0, err)))
+		if (!(bh = ext4_bread(NULL, dir, block, 0, err))) {
+			if (!(*err)) {
+				*err = -EIO;
+				ext4_error(dir->i_sb,
+					   "Directory hole detected on inode %lu\n",
+					   dir->i_ino);
+			}
 			goto errout;
+		}
 
 		if (!buffer_verified(bh) &&
 		    !ext4_dirent_csum_verify(dir,
@@ -1808,9 +1841,15 @@ static int ext4_add_entry(handle_t *handle, struct dentry *dentry,
 	}
 	blocks = dir->i_size >> sb->s_blocksize_bits;
 	for (block = 0; block < blocks; block++) {
-		bh = ext4_bread(handle, dir, block, 0, &retval);
-		if(!bh)
+		if (!(bh = ext4_bread(handle, dir, block, 0, &retval))) {
+			if (!retval) {
+				retval = -EIO;
+				ext4_error(inode->i_sb,
+					   "Directory hole detected on inode %lu\n",
+					   inode->i_ino);
+			}
 			return retval;
+		}
 		if (!buffer_verified(bh) &&
 		    !ext4_dirent_csum_verify(dir,
 				(struct ext4_dir_entry *)bh->b_data))
@@ -1867,8 +1906,15 @@ static int ext4_dx_add_entry(handle_t *handle, struct dentry *dentry,
 	entries = frame->entries;
 	at = frame->at;
 
-	if (!(bh = ext4_bread(handle,dir, dx_get_block(frame->at), 0, &err)))
+	if (!(bh = ext4_bread(handle, dir, dx_get_block(frame->at), 0, &err))) {
+		if (!err) {
+			err = -EIO;
+			ext4_error(dir->i_sb,
+				   "Directory hole detected on inode %lu\n",
+				   dir->i_ino);
+		}
 		goto cleanup;
+	}
 
 	if (!buffer_verified(bh) &&
 	    !ext4_dirent_csum_verify(dir, (struct ext4_dir_entry *)bh->b_data))
@@ -2204,9 +2250,15 @@ retry:
 	inode->i_op = &ext4_dir_inode_operations;
 	inode->i_fop = &ext4_dir_operations;
 	inode->i_size = EXT4_I(inode)->i_disksize = inode->i_sb->s_blocksize;
-	dir_block = ext4_bread(handle, inode, 0, 1, &err);
-	if (!dir_block)
+	if (!(dir_block = ext4_bread(handle, inode, 0, 1, &err))) {
+		if (!err) {
+			err = -EIO;
+			ext4_error(inode->i_sb,
+				   "Directory hole detected on inode %lu\n",
+				   inode->i_ino);
+		}
 		goto out_clear_inode;
+	}
 	BUFFER_TRACE(dir_block, "get_write_access");
 	err = ext4_journal_get_write_access(handle, dir_block);
 	if (err)
@@ -2323,6 +2375,11 @@ static int empty_dir(struct inode *inode)
 					EXT4_ERROR_INODE(inode,
 						"error %d reading directory "
 						"lblock %u", err, lblock);
+				else
+					ext4_warning(inode->i_sb,
+						"bad directory (dir #%lu) - no data block",
+						inode->i_ino);
+
 				offset += sb->s_blocksize;
 				continue;
 			}
@@ -2830,9 +2887,15 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
 				goto end_rename;
 		}
 		retval = -EIO;
-		dir_bh = ext4_bread(handle, old_inode, 0, 0, &retval);
-		if (!dir_bh)
+		if (!(dir_bh = ext4_bread(handle, old_inode, 0, 0, &retval))) {
+			if (!retval) {
+				retval = -EIO;
+				ext4_error(old_inode->i_sb,
+					   "Directory hole detected on inode %lu\n",
+					   old_inode->i_ino);
+			}
 			goto end_rename;
+		}
 		if (!buffer_verified(dir_bh) &&
 		    !ext4_dirent_csum_verify(old_inode,
 				(struct ext4_dir_entry *)dir_bh->b_data))