[PATCH] nilfs2: fix kernel bug on rename operation of broken directory

From: Ryusuke Konishi
Date: Fri Jun 28 2024 - 12:50:11 EST


Syzbot reported that in rename directory operation on broken directory
on nilfs2, __block_write_begin_int() called to prepare block write may
fail BUG_ON check for access exceeding the folio/page size.

This is because nilfs_dotdot(), which gets parent directory reference
entry ("..") of the directory to be moved or renamed, does not check
consistency enough, and may return location exceeding folio/page size
for broken directories.

Fix this issue by checking required directory entries ("." and "..")
in the first chunk of the directory in nilfs_dotdot().

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Reported-by: syzbot+d3abed1ad3d367fa2627@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=d3abed1ad3d367fa2627
Fixes: 2ba466d74ed7 ("nilfs2: directory entry operations")
Tested-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
Hi Andrew, please apply this as a bug fix.

This fixes a potential kernel bug reported by syzbot regarding broken
directory rename operations.

Thanks,
Ryusuke Konishi

fs/nilfs2/dir.c | 32 ++++++++++++++++++++++++++++++--
1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/fs/nilfs2/dir.c b/fs/nilfs2/dir.c
index dddfa604491a..4a29b0138d75 100644
--- a/fs/nilfs2/dir.c
+++ b/fs/nilfs2/dir.c
@@ -383,11 +383,39 @@ struct nilfs_dir_entry *nilfs_find_entry(struct inode *dir,

struct nilfs_dir_entry *nilfs_dotdot(struct inode *dir, struct folio **foliop)
{
- struct nilfs_dir_entry *de = nilfs_get_folio(dir, 0, foliop);
+ struct folio *folio;
+ struct nilfs_dir_entry *de, *next_de;
+ size_t limit;
+ char *msg;

+ de = nilfs_get_folio(dir, 0, &folio);
if (IS_ERR(de))
return NULL;
- return nilfs_next_entry(de);
+
+ limit = nilfs_last_byte(dir, 0); /* is a multiple of chunk size */
+ if (unlikely(!limit || le64_to_cpu(de->inode) != dir->i_ino ||
+ !nilfs_match(1, ".", de))) {
+ msg = "missing '.'";
+ goto fail;
+ }
+
+ next_de = nilfs_next_entry(de);
+ /*
+ * If "next_de" has not reached the end of the chunk, there is
+ * at least one more record. Check whether it matches "..".
+ */
+ if (unlikely((char *)next_de == (char *)de + nilfs_chunk_size(dir) ||
+ !nilfs_match(2, "..", next_de))) {
+ msg = "missing '..'";
+ goto fail;
+ }
+ *foliop = folio;
+ return next_de;
+
+fail:
+ nilfs_error(dir->i_sb, "directory #%lu %s", dir->i_ino, msg);
+ folio_release_kmap(folio, de);
+ return NULL;
}

ino_t nilfs_inode_by_name(struct inode *dir, const struct qstr *qstr)
--
2.34.1