Capture the UUID from packet 1 (request)

Make sure we capture only the first instance of the UUID, in case
the server does something silly like send back its own UUID.

diff --git a/pxelinux.asm b/pxelinux.asm
index 8003f89..ef4bf50 100644 (file)
--- a/pxelinux.asm
+++ b/pxelinux.asm
@@ -231,8 +231,10 @@ MAC                resb MAC_MAX+1          ; Actual MAC address
 BOOTIFStr      resb 7                  ; Space for "BOOTIF="
 MACStr         resb 3*(MAC_MAX+1)      ; MAC address as a string
 
-; One byte extra since dhcp_copyoption zero-terminates
-UUID           resb 16+1               ; UUID, from the PXE stack
+; The relative position of these fields matter!
+UUIDType       resb 1                  ; Type byte from DHCP option
+UUID           resb 16                 ; UUID, from the PXE stack
+UUIDNull       resb 1                  ; dhcp_copyoption zero-terminates
 
 ;
 ; PXE packets which don't need static initialization
@@ -2279,12 +2281,11 @@ dopt_%2:
        dopt 97, uuid_client_identifier
                cmp ax,17               ; type byte + 16 bytes UUID
                jne .skip
-               cmp [si],ah             ; type 0 == UUID
-               jne .skip
-               inc si
-               dec ax
+               mov dl,[si]             ; Must have type 0 == UUID
+               or dl,[HaveUUID]        ; Capture only the first instance
+               jnz .skip
                mov byte [HaveUUID],1   ; Got UUID
-               mov di,UUID
+               mov di,UUIDType
                jmp dhcp_copyoption
 .skip:         ret