[PATCH] f2fs: fix to prevent clearing immutable for large folio supported inode

[Chao Yu <chao@kernel.org>]

Below testcase can change large folio supported inode from immutable
to mutable, it's not as expected, let's add a new check condition in
f2fs_setflags_common() to detect and reject it.

- dd if=/dev/zero of=/mnt/f2fs/test bs=32k count=4
- f2fs_io setflags immutable /mnt/f2fs/test
- echo 3 > /proc/sys/vm/drop_caches
 : to reload inode with large folio
- f2fs_io read 32 0 1 mmap 0 0 /mnt/f2fs/test
- f2fs_io clearflags immutable /mnt/f2fs/test

Signed-off-by: Chao Yu <chao@kernel.org>
---
 fs/f2fs/file.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index ce291f152bc3..f7f9da0b215f 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -2155,6 +2155,12 @@ static int f2fs_setflags_common(struct inode *inode, u32 iflags, u32 mask)
 		}
 	}
 
+	if ((iflags ^ masked_flags) & F2FS_IMMUTABLE_FL) {
+		if ((masked_flags & F2FS_IMMUTABLE_FL) &&
+			mapping_large_folio_support(inode->i_mapping))
+			return -EINVAL;
+	}
+
 	fi->i_flags = iflags | (fi->i_flags & ~mask);
 	f2fs_bug_on(F2FS_I_SB(inode), (fi->i_flags & F2FS_COMPR_FL) &&
 					(fi->i_flags & F2FS_NOCOMP_FL));
-- 
2.40.1