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ref: 9d15403fda575ab73c5501970fe3835265b05aee
parent: 7b4e3be27e510fd93f46c8a10375c509f868df92
author: cinap_lenrek <[email protected]>
date: Sun Oct 31 08:39:46 EDT 2021

libc: fix overflow of domain component rune buffer for idn2utf()

If the source string has a run of more than 256 runes without
a "." dot, we'd overflow the runebuffer in idn2utf().

The utf2idn() routine had a check in the while loop, but that
is actually wrong too, as it would insert a dot and restart
the loop in the middle of a domain component. Just error
out if a domain component is too long.

--- a/sys/src/libc/9sys/idn.c

+++ b/sys/src/libc/9sys/idn.c

@@ -200,6 +200,8 @@

 			n = chartorune(&r, cp+nc);

 			if(r == '.')

 				break;

+			if(nr >= nelem(rb))

+				return -1;

 			rb[nr++] = r;

 			nc += n;

 		}

@@ -234,10 +236,12 @@

 	cp = name;

 	for(;;){

 		nc = nr = 0;

-		while(cp[nc] != 0 && nr < nelem(rb)){

+		while(cp[nc] != 0){

 			n = chartorune(&r, cp+nc);

 			if(r == '.')

 				break;

+			if(nr >= nelem(rb))

+				return -1;

 			rb[nr++] = r;

 			nc += n;

 		}