[PATCH 4.9 069/111] cifs: prevent integer overflow in nxt_dir_entry()

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

commit 8ad8aa353524d89fa2e09522f3078166ff78ec42 upstream.

The "old_entry + le32_to_cpu(pDirInfo->NextEntryOffset)" can wrap
around so I have added a check for integer overflow.

Reported-by: Dr Silvio Cesare of InfoSect <silvio.cesare@xxxxxxxxx>
Reviewed-by: Ronnie Sahlberg <lsahlber@xxxxxxxxxx>
Reviewed-by: Aurelien Aptel <aaptel@xxxxxxxx>
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
CC: Stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/cifs/readdir.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

--- a/fs/cifs/readdir.c
+++ b/fs/cifs/readdir.c
@@ -376,8 +376,15 @@ static char *nxt_dir_entry(char *old_ent
 
 		new_entry = old_entry + sizeof(FIND_FILE_STANDARD_INFO) +
 				pfData->FileNameLength;
-	} else
-		new_entry = old_entry + le32_to_cpu(pDirInfo->NextEntryOffset);
+	} else {
+		u32 next_offset = le32_to_cpu(pDirInfo->NextEntryOffset);
+
+		if (old_entry + next_offset < old_entry) {
+			cifs_dbg(VFS, "invalid offset %u\n", next_offset);
+			return NULL;
+		}
+		new_entry = old_entry + next_offset;
+	}
 	cifs_dbg(FYI, "new entry %p old entry %p\n", new_entry, old_entry);
 	/* validate that new_entry is not past end of SMB */
 	if (new_entry >= end_of_smb) {