[PATCH] f2fs: reject overlapping move range after len expansion

[Hao-Qun Huang]

F2FS_IOC_MOVE_RANGE treats a zero length as a request to move data
from pos_in to EOF. However, the same-file overlap check runs before
that expansion, so a request with len == 0 bypasses the overlap
rejection added for same-file moves.

For example, with a four-block file, moving from block 0 to block 1
with len == 0 is accepted by the old check because pos_in + len is
still pos_in at that point. The code then expands len to cover the
rest of the file and calls __exchange_data_block() on overlapping
source and destination ranges in the same inode, which is the
data-corruption case the overlap check was meant to reject.

Move the overlap check after the source range has been validated and
len == 0 has been expanded, so it sees the effective length. This is a
no-op for non-zero len (the value is unchanged there) and keeps the
existing early return for identical positions.

Fixes: d95fd91c1ac1 ("f2fs: exclude special cases for f2fs_move_file_range")
Cc: stable@xxxxxxxxxxxxxxx
Assisted-by: Claude:claude-fable-5
Signed-off-by: Hao-Qun Huang <alvinhuang0603@xxxxxxxxx>
---
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 4b52c56d71f0..fdfef01dc799 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -3144,8 +3144,6 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
 	if (src == dst) {
 		if (pos_in == pos_out)
 			return 0;
-		if (pos_out > pos_in && pos_out < pos_in + len)
-			return -EINVAL;
 	}
 
 	inode_lock(src);
@@ -3171,6 +3169,8 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
 		goto out_unlock;
 	if (len == 0)
 		olen = len = src->i_size - pos_in;
+	if (src == dst && pos_out > pos_in && pos_out < pos_in + len)
+		goto out_unlock;
 	if (pos_in + len == src->i_size)
 		len = ALIGN(src->i_size, F2FS_BLKSIZE) - pos_in;
 	if (len == 0) {
-- 
2.43.0