cifs: prevent integer overflow in nxt_dir_entry()

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@gmail.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
CC: Stable <stable@vger.kernel.org>

diff --git a/fs/cifs/readdir.c b/fs/cifs/readdir.c
index eeab81c9452f86e61948198b0d938ea8b6a9a5dd..e169e1a5fd358c5ac9649f1f24e7a4fb876d3635 100644 (file)
--- a/fs/cifs/readdir.c
+++ b/fs/cifs/readdir.c
@@ -376,8 +376,15 @@ static char *nxt_dir_entry(char *old_entry, char *end_of_smb, int level)
 
                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) {