cifs: check for bytes_remaining going to zero in CIFS_SessSetup

It's possible that when we go to decode the string area in the
SESSION_SETUP response, that bytes_remaining will be 0. Decrementing it at
that point will mean that it can go "negative" and wrap. Check for a
bytes_remaining value of 0, and don't try to decode the string area if
that's the case.

Cc: stable@kernel.org
Reported-and-Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

diff --git a/fs/cifs/sess.c b/fs/cifs/sess.c
index 2e2c911035297d1349d5fbd2b0908736b819db8e..645114ad0a10031e08ad9beaa815a720b9fe50b0 100644 (file)
--- a/fs/cifs/sess.c
+++ b/fs/cifs/sess.c
@@ -916,7 +916,9 @@ ssetup_ntlmssp_authenticate:
        }
 
        /* BB check if Unicode and decode strings */
-       if (smb_buf->Flags2 & SMBFLG2_UNICODE) {
+       if (bytes_remaining == 0) {
+               /* no string area to decode, do nothing */
+       } else if (smb_buf->Flags2 & SMBFLG2_UNICODE) {
                /* unicode string area must be word-aligned */
                if (((unsigned long) bcc_ptr - (unsigned long) smb_buf) % 2) {
                        ++bcc_ptr;