[PATCH 5.15.y 2/2] f2fs: validate compress cache inode only when enabled

[Sasha Levin <sashal@kernel.org>]

From: Wenjie Qi <qwjhust@gmail.com>

[ Upstream commit 5073c66a96a9c23c0c2533ed4ed06e42f9021208 ]

F2FS_COMPRESS_INO() uses NM_I(sbi)->max_nid as the synthetic inode
number for the compressed page cache inode. That inode only exists when
the compress_cache mount option is enabled.

When compress_cache is disabled, max_nid is outside the valid inode
range. A corrupted directory entry that points to ino == max_nid should
therefore be rejected by f2fs_check_nid_range(). However, is_meta_ino()
currently treats F2FS_COMPRESS_INO() as a meta inode unconditionally,
so f2fs_iget() bypasses do_read_inode() and its nid range check, and
instantiates a fake internal inode instead.

Gate the compressed cache inode case on COMPRESS_CACHE, matching
f2fs_init_compress_inode(). With compress_cache disabled, ino ==
max_nid now follows the normal inode path and is rejected as an
out-of-range nid.

Cc: stable@kernel.org
Fixes: 6ce19aff0b8c ("f2fs: compress: add compress_inode to cache compressed blocks")
Signed-off-by: Wenjie Qi <qiwenjie@xiaomi.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/f2fs/inode.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 4a99a9eab8291d..7b387edb6ef642 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -498,8 +498,13 @@ static int do_read_inode(struct inode *inode)
 
 static bool is_meta_ino(struct f2fs_sb_info *sbi, unsigned int ino)
 {
-	return ino == F2FS_NODE_INO(sbi) || ino == F2FS_META_INO(sbi) ||
-		ino == F2FS_COMPRESS_INO(sbi);
+	if (ino == F2FS_NODE_INO(sbi) || ino == F2FS_META_INO(sbi))
+		return true;
+#ifdef CONFIG_F2FS_FS_COMPRESSION
+	if (test_opt(sbi, COMPRESS_CACHE) && ino == F2FS_COMPRESS_INO(sbi))
+		return true;
+#endif
+	return false;
 }
 
 struct inode *f2fs_iget(struct super_block *sb, unsigned long ino)
-- 
2.53.0