[PATCH] ntfs: fix memmove overlap in ntfs_new_attr_flags

[Hongling Zeng]

When the record shrinks while the payload offsets increase (e.g., enabling
compression reduces padding, making arec_size < old_arec_size, but the header
grows by 8 bytes), moving the name first can overwrite the old mapping_pairs
before they are copied. Move mapping_pairs first in this case.

Since mp_ofs is derived from name_ofs, they always change in the same
direction. Checking name_ofs alone is sufficient.

Fixes: fc053f05ca28 ("ntfs: add reparse and ea operations")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Hongling Zeng <zenghongling@xxxxxxxxxx>
---
 fs/ntfs/ea.c | 33 +++++++++++++++++++++++++++------
 1 file changed, 27 insertions(+), 6 deletions(-)

diff --git a/fs/ntfs/ea.c b/fs/ntfs/ea.c
index 534f7efaf128..c836d33ab0d3 100644
--- a/fs/ntfs/ea.c
+++ b/fs/ntfs/ea.c
@@ -729,15 +729,36 @@ static int ntfs_new_attr_flags(struct ntfs_inode *ni, __le32 fattr)
 	old_arec_size = le32_to_cpu(a->length);
 
 	/*
-	 * Move payloads before shrinking the record.  Otherwise resizing moves
+	 * Move payloads before shrinking the record. Otherwise resizing moves
 	 * the following attribute over the old payload before it can be copied.
+	 *
+	 * When offsets increase, move mapping_pairs first to avoid name
+	 * overwriting the start of mapping_pairs.
 	 */
 	if (arec_size < old_arec_size) {
-		if (a->name_length && name_ofs != old_name_ofs)
-			memmove((u8 *)a + name_ofs, (u8 *)a + old_name_ofs,
-				a->name_length * sizeof(__le16));
-		if (mp_ofs != old_mp_ofs)
-			memmove((u8 *)a + mp_ofs, (u8 *)a + old_mp_ofs, mp_size);
+		if (name_ofs > old_name_ofs) {
+			/* Payload offsets increased: move mapping pairs first. */
+			if (mp_ofs != old_mp_ofs)
+				memmove((u8 *)a + mp_ofs,
+						(u8 *)a + old_mp_ofs,
+						mp_size);
+			if (a->name_length && name_ofs != old_name_ofs)
+				memmove((u8 *)a + name_ofs,
+						(u8 *)a + old_name_ofs,
+						a->name_length *
+							sizeof(__le16));
+		} else {
+			/* Payload offsets decreased or unchanged: move name first. */
+			if (a->name_length && name_ofs != old_name_ofs)
+				memmove((u8 *)a + name_ofs,
+						(u8 *)a + old_name_ofs,
+						a->name_length *
+							sizeof(__le16));
+			if (mp_ofs != old_mp_ofs)
+				memmove((u8 *)a + mp_ofs,
+						(u8 *)a + old_mp_ofs,
+						mp_size);
+		}
 	}
 
 	err = ntfs_attr_record_resize(ctx->mrec, a, arec_size);
-- 
2.25.1