From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org
X-Spam-Level: 
X-Spam-Status: No, score=-0.0 required=5.0 tests=T_SCC_BODY_TEXT_LINE
	autolearn=ham autolearn_force=no version=3.4.4
Received: (qmail 16971 invoked from network); 16 Jul 2022 17:23:41 -0000
Received: from 9front.inri.net (168.235.81.73)
  by inbox.vuxu.org with ESMTPUTF8; 16 Jul 2022 17:23:41 -0000
Received: from mimir.eigenstate.org ([206.124.132.107]) by 9front; Sat Jul 16 13:20:21 -0400 2022
Received: from abbatoir.myfiosgateway.com (pool-74-108-56-225.nycmny.fios.verizon.net [74.108.56.225])
	by mimir.eigenstate.org (OpenSMTPD) with ESMTPSA id 59aec68a (TLSv1.2:ECDHE-RSA-AES256-SHA:256:NO)
	for <9front@9front.org>;
	Sat, 16 Jul 2022 10:20:12 -0700 (PDT)
Message-ID: <27B7D72DA37DE45025E223A1A74E63C0@eigenstate.org>
To: 9front@9front.org
Date: Sat, 16 Jul 2022 13:20:11 -0400
From: ori@eigenstate.org
In-Reply-To: <FA4664774E39346AC2EC9A9EBE02AD91@felloff.net>
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit
List-ID: <9front.9front.org>
List-Help: <http://lists.9front.org>
X-Glyph: ➈
X-Bullshit: virtual hosting configuration session singleton 
Subject: Re: [9front] sysproc: raise limit on shebang lines, handle quoting.
Reply-To: 9front@9front.org
Precedence: bulk

Quoth cinap_lenrek@felloff.net:
> > -	s += 2;
> > -	n -= 2;		/* skip #! */
> 
> i'd keep these lines, avoiding the multiple s+2 expressions
> down the road.
> 
> my main concern is making sure we'r not blowing the stack
> with this change on archs with small 4k stacks like 32bit arm.
> 
> just need to checks...
> 
> also:
> 
> > +			ehdr = (void*)buf;
> 
> not sure if that will yield properly aligned ehdr pointer as
> buf is just char[]. i think that was the reason it was a union
> before.
> 
> otherwise looks ok.

Thanks, and updated. Changes from last round:

- Use s+=2 as before
- Add stack size assert (can be removed before committing?)
- Bump buffer to 256, since it turned out we have more than
  enough space. On 386, we have 0xbb0 stack left by the time
  we call sysexec. 128 is workable, but I actually ran into
  it with a particularly insane auth/box call...
- Use a union instead of casting; it doesn't matter much,
  but I didn't like copying the exec header around. :)

diff 8f1954c0dd4ca231d6904fbbd788dbe40ef284e3 uncommitted
--- a/sys/src/9/port/sysproc.c
+++ b/sys/src/9/port/sysproc.c
@@ -243,35 +243,17 @@
 }
 
 static int
-shargs(char *s, int n, char **ap)
+shargs(char *s, int n, char **ap, int nap)
 {
+	char *p;
 	int i;
 
 	if(n <= 2 || s[0] != '#' || s[1] != '!')
 		return -1;
-	s += 2;
-	n -= 2;		/* skip #! */
-	for(i=0;; i++){
-		if(i >= n)
-			return 0;
-		if(s[i]=='\n')
-			break;
-	}
-	s[i] = 0;
-
-	i = 0;
-	for(;;) {
-		while(*s==' ' || *s=='\t')
-			s++;
-		if(*s == 0)
-			break;
-		ap[i++] = s++;
-		while(*s && *s!=' ' && *s!='\t')
-			s++;
-		if(*s == 0)
-			break;
-		*s++ = 0;
-	}
+	if((p = memchr(s+2, '\n', n-2)) == nil)
+		return 0;
+	*p = 0;
+	i = tokenize(s+2, ap, nap-1);
 	ap[i] = nil;
 	return i;
 }
@@ -297,15 +279,25 @@
 				  | (uvlong)p[7];
 }
 
+intptr
+stackspace(void)
+{
+	int sval;
+	return (intptr)&sval - (intptr)up->kstack;
+}
+
 uintptr
 sysexec(va_list list)
 {
-	struct {
-		Exec;
-		uvlong	hdr[1];
+	union {
+		struct {
+			Exec;
+			uvlong	hdr[1];
+		};
+		char buf[256];
 	} ehdr;
-	char line[sizeof(ehdr)];
-	char *progarg[sizeof(line)/2+1];
+	char line[256];
+	char *progarg[64+1];
 	volatile char *args, *elem, *file0;
 	char **argv, **argp, **argp0;
 	char *a, *e, *charp, *file;
@@ -318,6 +310,8 @@
 	Chan *tc;
 	Fgrp *f;
 
+	/* We put big uffers on the stack, make sure we have room to keep going */
+	assert(stackspace() > 512);
 	args = elem = nil;
 	file0 = va_arg(list, char*);
 	validaddr((uintptr)file0, 1, 0);
@@ -353,7 +347,7 @@
 		if(!indir)
 			kstrdup(&elem, up->genbuf);
 
-		n = devtab[tc->type]->read(tc, &ehdr, sizeof(ehdr), 0);
+		n = devtab[tc->type]->read(tc, ehdr.buf, sizeof(ehdr.buf), 0);
 		if(n >= sizeof(Exec)) {
 			magic = beswal(ehdr.magic);
 			if(magic == AOUT_MAGIC) {
@@ -393,8 +387,8 @@
 		/*
 		 * Process #! /bin/sh args ...
 		 */
-		memmove(line, &ehdr, n);
-		n = shargs(line, n, progarg);
+		memmove(line, ehdr.buf, n);
+		n = shargs(line, n, progarg, nelem(progarg));
 		if(n < 1)
 			error(Ebadexec);
 		/*