nilfs2: handle errors that nilfs_prepare_chunk() may return

Patch series "nilfs2: fix issues with rename operations".

This series fixes BUG_ON check failures reported by syzbot around rename
operations, and a minor behavioral issue where the mtime of a child
directory changes when it is renamed instead of moved.


This patch (of 2):

The directory manipulation routines nilfs_set_link() and
nilfs_delete_entry() rewrite the directory entry in the folio/page
previously read by nilfs_find_entry(), so error handling is omitted on the
assumption that nilfs_prepare_chunk(), which prepares the buffer for
rewriting, will always succeed for these.  And if an error is returned, it
triggers the legacy BUG_ON() checks in each routine.

This assumption is wrong, as proven by syzbot: the buffer layer called by
nilfs_prepare_chunk() may call nilfs_get_block() if necessary, which may
fail due to metadata corruption or other reasons.  This has been there all
along, but improved sanity checks and error handling may have made it more
reproducible in fuzzing tests.

Fix this issue by adding missing error paths in nilfs_set_link(),
nilfs_delete_entry(), and their caller nilfs_rename().

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ryusuke Konishi <[email protected]>
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=32c3706ebf5d95046ea1
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=1097e95f134f37d9395c
Fixes: 2ba466d ("nilfs2: directory entry operations")
Signed-off-by: Andrew Morton <[email protected]>

Author: konis

fs/nilfs2/dir.c

@@ -400,7 +400,7 @@ int nilfs_inode_by_name(struct inode *dir, const struct qstr *qstr, ino_t *ino)
 	return 0;
 }
 
-void nilfs_set_link(struct inode *dir, struct nilfs_dir_entry *de,
+int nilfs_set_link(struct inode *dir, struct nilfs_dir_entry *de,
 		    struct folio *folio, struct inode *inode)
 {
 	size_t from = offset_in_folio(folio, de);
@@ -410,11 +410,15 @@ void nilfs_set_link(struct inode *dir, struct nilfs_dir_entry *de,
 
 	folio_lock(folio);
 	err = nilfs_prepare_chunk(folio, from, to);
-	BUG_ON(err);
+	if (unlikely(err)) {
+		folio_unlock(folio);
+		return err;
+	}
 	de->inode = cpu_to_le64(inode->i_ino);
 	de->file_type = fs_umode_to_ftype(inode->i_mode);
 	nilfs_commit_chunk(folio, mapping, from, to);
 	inode_set_mtime_to_ts(dir, inode_set_ctime_current(dir));
+	return 0;
 }
 
 /*
@@ -543,7 +547,10 @@ int nilfs_delete_entry(struct nilfs_dir_entry *dir, struct folio *folio)
 		from = (char *)pde - kaddr;
 	folio_lock(folio);
 	err = nilfs_prepare_chunk(folio, from, to);
-	BUG_ON(err);
+	if (unlikely(err)) {
+		folio_unlock(folio);
+		goto out;
+	}
 	if (pde)
 		pde->rec_len = nilfs_rec_len_to_disk(to - from);
 	dir->inode = 0;

fs/nilfs2/namei.c

@@ -406,8 +406,10 @@ static int nilfs_rename(struct mnt_idmap *idmap,
 			err = PTR_ERR(new_de);
 			goto out_dir;
 		}
-		nilfs_set_link(new_dir, new_de, new_folio, old_inode);
+		err = nilfs_set_link(new_dir, new_de, new_folio, old_inode);
 		folio_release_kmap(new_folio, new_de);
+		if (unlikely(err))
+			goto out_dir;
 		nilfs_mark_inode_dirty(new_dir);
 		inode_set_ctime_current(new_inode);
 		if (dir_de)
@@ -430,28 +432,27 @@ static int nilfs_rename(struct mnt_idmap *idmap,
 	 */
 	inode_set_ctime_current(old_inode);
 
-	nilfs_delete_entry(old_de, old_folio);
-
-	if (dir_de) {
-		nilfs_set_link(old_inode, dir_de, dir_folio, new_dir);
-		folio_release_kmap(dir_folio, dir_de);
-		drop_nlink(old_dir);
+	err = nilfs_delete_entry(old_de, old_folio);
+	if (likely(!err)) {
+		if (dir_de) {
+			err = nilfs_set_link(old_inode, dir_de, dir_folio,
+					     new_dir);
+			drop_nlink(old_dir);
+		}
+		nilfs_mark_inode_dirty(old_dir);
 	}
-	folio_release_kmap(old_folio, old_de);
-
-	nilfs_mark_inode_dirty(old_dir);
 	nilfs_mark_inode_dirty(old_inode);
 
-	err = nilfs_transaction_commit(old_dir->i_sb);
-	return err;
-
 out_dir:
 	if (dir_de)
 		folio_release_kmap(dir_folio, dir_de);
 out_old:
 	folio_release_kmap(old_folio, old_de);
 out:
-	nilfs_transaction_abort(old_dir->i_sb);
+	if (likely(!err))
+		err = nilfs_transaction_commit(old_dir->i_sb);
+	else
+		nilfs_transaction_abort(old_dir->i_sb);
 	return err;
 }
 

fs/nilfs2/nilfs.h

@@ -261,8 +261,8 @@ struct nilfs_dir_entry *nilfs_find_entry(struct inode *, const struct qstr *,
 int nilfs_delete_entry(struct nilfs_dir_entry *, struct folio *);
 int nilfs_empty_dir(struct inode *);
 struct nilfs_dir_entry *nilfs_dotdot(struct inode *, struct folio **);
-void nilfs_set_link(struct inode *, struct nilfs_dir_entry *,
-			   struct folio *, struct inode *);
+int nilfs_set_link(struct inode *dir, struct nilfs_dir_entry *de,
+		   struct folio *folio, struct inode *inode);
 
 /* file.c */
 extern int nilfs_sync_file(struct file *, loff_t, loff_t, int);