linux-kernel - [PATCH] fuse: Move same-superblock check to fuse_copy_file

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Message-ID: <20250806135254.352-1-luochunsheng@ustc.edu>
Date: Wed,  6 Aug 2025 21:52:54 +0800
From: Chunsheng Luo <luochunsheng@...c.edu>
To: miklos@...redi.hu
Cc: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Chunsheng Luo <luochunsheng@...c.edu>
Subject: [PATCH] fuse: Move same-superblock check to fuse_copy_file_range

The copy_file_range COPY_FILE_SPLICE capability allows filesystems to
handle cross-superblock copy. However, in the current fuse implementation,
__fuse_copy_file_range accesses src_file->private_data under the assumption
that it points to a fuse_file structure. When the source file belongs to a
non-FUSE filesystem, it will leads to kernel panics.

To resolve this, move the same-superblock check from __fuse_copy_file_range
to fuse_copy_file_range to ensure both files belong to the same fuse
superblock before accessing private_data.

Signed-off-by: Chunsheng Luo <luochunsheng@...c.edu>
---
 fs/fuse/file.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 95275a1e2f54..a29f1b84f11b 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2984,9 +2984,6 @@ static ssize_t __fuse_copy_file_range(struct file *file_in, loff_t pos_in,
 	if (fc->no_copy_file_range)
 		return -EOPNOTSUPP;
 
-	if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
-		return -EXDEV;
-
 	inode_lock(inode_in);
 	err = fuse_writeback_range(inode_in, pos_in, pos_in + len - 1);
 	inode_unlock(inode_in);
@@ -3066,9 +3063,12 @@ static ssize_t fuse_copy_file_range(struct file *src_file, loff_t src_off,
 {
 	ssize_t ret;
 
+	if (file_inode(src_file)->i_sb != file_inode(dst_file)->i_sb)
+		return splice_copy_file_range(src_file, src_off, dst_file,
+					     dst_off, len);
+
 	ret = __fuse_copy_file_range(src_file, src_off, dst_file, dst_off,
 				     len, flags);
-
 	if (ret == -EOPNOTSUPP || ret == -EXDEV)
 		ret = splice_copy_file_range(src_file, src_off, dst_file,
 					     dst_off, len);
-- 
2.43.0