From 520a39efcd135556b21e196bfd64802fd3236ce1 Mon Sep 17 00:00:00 2001
From: Ori Bernstein <ori@eigenstate.org>
Date: Mon, 25 Jul 2022 04:48:44 +0000
Subject: [PATCH] sysproc: raise limit on #! lines, and allow quoted args
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Our #! line length is very short, and the naïve quoting
makes it difficult to pass more complicated arguments to
the programs being run. This is fine for simple interpreters,
but it's often useful to pass arguments to more complicated
interpreters like auth/box or awk.

This change raises the limit, but also switches to tokenizing
via tokenize(2), rather than hand rolled whitespace splitting.

The limits chosen are arbitrary, but they leave approximately
3 KiB of stack space on 386, and 13k on amd64. This is a lot
of stack used, but it should leave enough for fairly deep
devtab chan stacks.
---
 sys/man/2/exec           |  5 ++++
 sys/src/9/port/sysproc.c | 65 ++++++++++++++++------------------------
 2 files changed, 31 insertions(+), 39 deletions(-)

diff --git a/sys/man/2/exec b/sys/man/2/exec
index 9c9d4134b..dc7551d02 100644
--- a/sys/man/2/exec
+++ b/sys/man/2/exec
@@ -67,6 +67,11 @@ and any initial arguments to that program, for example
 ls | mc
 .EE
 .PP
+There may be up to 256 bytes of arguments passed to the interpreter.
+These are tokenized into up to 32 arguments by
+.IR tokenize (2)
+before being passed as the interpreters argument vector.
+.PP
 When a C program is executed,
 it is called as follows:
 .IP
diff --git a/sys/src/9/port/sysproc.c b/sys/src/9/port/sysproc.c
index bb25b2b4b..cd1e641cb 100644
--- a/sys/src/9/port/sysproc.c
+++ b/sys/src/9/port/sysproc.c
@@ -243,35 +243,19 @@ sysrfork(va_list list)
 }
 
 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, '\n', n)) == nil)
+		return 0;
+	*p = 0;
+	i = tokenize(s, ap, nap-1);
 	ap[i] = nil;
 	return i;
 }
@@ -300,12 +284,15 @@ beswav(uvlong v)
 uintptr
 sysexec(va_list list)
 {
-	struct {
-		Exec;
-		uvlong	hdr[1];
-	} ehdr;
-	char line[sizeof(ehdr)];
-	char *progarg[sizeof(line)/2+1];
+	union {
+		struct {
+			Exec;
+			uvlong	hdr[1];
+		} ehdr;
+		char buf[256];
+	} u;
+	char line[256];
+	char *progarg[32+1];
 	volatile char *args, *elem, *file0;
 	char **argv, **argp, **argp0;
 	char *a, *e, *charp, *file;
@@ -353,22 +340,22 @@ sysexec(va_list list)
 		if(!indir)
 			kstrdup(&elem, up->genbuf);
 
-		n = devtab[tc->type]->read(tc, &ehdr, sizeof(ehdr), 0);
+		n = devtab[tc->type]->read(tc, u.buf, sizeof(u.buf), 0);
 		if(n >= sizeof(Exec)) {
-			magic = beswal(ehdr.magic);
+			magic = beswal(u.ehdr.magic);
 			if(magic == AOUT_MAGIC) {
 				if(magic & HDR_MAGIC) {
-					if(n < sizeof(ehdr))
+					if(n < sizeof(u.ehdr))
 						error(Ebadexec);
-					entry = beswav(ehdr.hdr[0]);
-					text = UTZERO+sizeof(ehdr);
+					entry = beswav(u.ehdr.hdr[0]);
+					text = UTZERO+sizeof(u.ehdr);
 				} else {
-					entry = beswal(ehdr.entry);
+					entry = beswal(u.ehdr.entry);
 					text = UTZERO+sizeof(Exec);
 				}
 				if(entry < text)
 					error(Ebadexec);
-				text += beswal(ehdr.text);
+				text += beswal(u.ehdr.text);
 				if(text <= entry || text >= (USTKTOP-USTKSIZE))
 					error(Ebadexec);
 
@@ -393,8 +380,8 @@ sysexec(va_list list)
 		/*
 		 * Process #! /bin/sh args ...
 		 */
-		memmove(line, &ehdr, n);
-		n = shargs(line, n, progarg);
+		memmove(line, u.buf, n);
+		n = shargs(line, n, progarg, nelem(progarg));
 		if(n < 1)
 			error(Ebadexec);
 		/*
@@ -411,8 +398,8 @@ sysexec(va_list list)
 
 	t = (text+align) & ~align;
 	text -= UTZERO;
-	data = beswal(ehdr.data);
-	bss = beswal(ehdr.bss);
+	data = beswal(u.ehdr.data);
+	bss = beswal(u.ehdr.bss);
 	align = BY2PG-1;
 	d = (t + data + align) & ~align;
 	bssend = t + data + bss;