From: H. Peter Anvin <hpa@zytor.com>
Date: Tue, 9 Jun 2009 14:29:13 +0000 (-0700)
Subject: pxelinux: cleaner test for OACK trailing null bytes
X-Git-Tag: syslinux-3.82~2
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=1feb9b05ea0b9690a5e5af8b5919d63d6979a2eb;p=platform%2Fupstream%2Fsyslinux.git

pxelinux: cleaner test for OACK trailing null bytes

Instead of looking for a string of null bytes at the end of the OACK
string, simply abort parsing if we run into a null byte where an
option is expected; either we are seeing junk at the end of the
packet, or we are hopelessly confused about how to make sense of the
rest of the packet -- in either case, ignoring is the "liberal"
option.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
---

diff --git a/core/pxelinux.asm b/core/pxelinux.asm
index de1b10c..cbfae52 100644
--- a/core/pxelinux.asm
+++ b/core/pxelinux.asm
@@ -1105,16 +1105,16 @@ searchdir:
 		;  SI -> first byte of options; [E]CX -> byte count
 .parse_oack:
 		jcxz .done_pkt			; No options acked
-.get_opt_name:
-		; Some TFTP servers have junk NUL bytes at the end of the packet.
-		; If all that is left is NUL, then consider the packet processed.
-		mov di,si
-		push cx
-		xor ax,ax
-		repz scasb
-		pop cx
-		jz .done_pkt
+		; If we find an option which starts with a NUL byte,
+		; (a null option), we're either seeing garbage that some
+		; TFTP servers add to the end of the packet, or we have
+		; no clue how to parse the rest of the packet (what is
+		; an option name and what is a value?)  In either case,
+		; discard the rest.
+		cmp byte [si],0
+		je .done_pkt
 
+.get_opt_name:
 		mov di,si
 		mov bx,si
 .opt_name_loop:	lodsb