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kernel: reset up->setargs on sysexec(), fix race with devproc

up->setargs wasnt reset in sysexec(). also, up->args should only
be exchanged/freed under up->debug qlock. otherwise double free
could happen.

--- a/sys/src/9/port/portdat.h

+++ b/sys/src/9/port/portdat.h

@@ -737,7 +737,7 @@

 	ulong	qpc;		/* pc calling last blocking qlock */

 	QLock	*eql;		/* interruptable eqlock */

-	int	setargs;

+	int	setargs;	/* process changed its args */

 	void	*ureg;		/* User registers for notes */

 	void	*dbgreg;	/* User registers for devproc */

--- a/sys/src/9/port/sysproc.c

+++ b/sys/src/9/port/sysproc.c

@@ -252,19 +252,20 @@

 	ulong magic, text, entry, data, bss;

 	Tos *tos;

-	indir = 0;

+	a = nil;

 	elem = nil;

 	validaddr(arg[0], 1, 0);

 	file0 = validnamedup((char*)arg[0], 1);

 	if(waserror()){

 		free(file0);

-		if(elem != up->text)

-			free(elem);

+		free(elem);

+		free(a);

 		/* Disaster after commit */

 		if(!up->seg[SSEG])

 			pexit(up->errstr, 1);

 		nexterror();

 	}

+	indir = 0;

 	file = file0;

 	for(;;){

 		tc = namec(file, Aopen, OEXEC, 0);

@@ -405,28 +406,21 @@

 		charp += n;

 	}

-	free(up->text);

-	up->text = elem;

-

 	/* copy args; easiest from new process's stack */

 	n = charp - args;

 	if(n > 128)	/* don't waste too much space on huge arg lists */

 		n = 128;

-	a = up->args;

-	up->args = nil;

-	free(a);

-	up->args = smalloc(n);

-	memmove(up->args, args, n);

-	if(n>0 && up->args[n-1]!='\0'){

+	a = smalloc(n);

+	memmove(a, args, n);

+	if(n>0 && a[n-1]!='\0'){

 		/* make sure last arg is NUL-terminated */

 		/* put NUL at UTF-8 character boundary */

 		for(i=n-1; i>0; --i)

-			if(fullrune(up->args+i, n-i))

+			if(fullrune(a+i, n-i))

 				break;

-		up->args[i] = 0;

+		a[i] = 0;

 		n = i+1;

 	}

-	up->nargs = n;

 	/*

 	 * Committed.

@@ -501,6 +495,13 @@

 	free(file0);

 	qlock(&up->debug);

+	free(up->text);

+	up->text = elem;

+	free(up->args);

+	up->args = a;

+	up->nargs = n;

+	up->setargs = 0;

+

 	up->nnote = 0;

 	up->notify = 0;

 	up->notified = 0;

-- 

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