From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <a1044862c8d3f5cd9a577d545ea80deb@felloff.net>
Date: Sun, 27 Nov 2016 21:20:38 +0100
From: cinap_lenrek@felloff.net
To: 9fans@9fans.net
In-Reply-To: <583AF47A.4010400@mailinator.com>
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
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Subject: Re: [9fans] snprintf buffer overrun
Topicbox-Message-UUID: af5bdcea-ead9-11e9-9d60-3106f5b1d025

theres a bug is in sclose() where it doesnt check if wp is beyond
the buffer. also wp was not updated after realloc().

--- a/sys/src/libstdio/sclose.c	Sat Nov 19 16:47:21 2016 +0100
+++ b/sys/src/libstdio/sclose.c	Sun Nov 27 21:07:48 2016 +0100
@@ -5,27 +5,35 @@
 char *sclose(FILE *f){
 	switch(f->state){
 	default:	/* ERR CLOSED */
+	Error:
 		if(f->buf && f->flags&BALLOC)
 			free(f->buf);
-		f->flags=0;
-		return NULL;
+		f->buf=0;
+		break;
 	case OPEN:
 		f->buf=malloc(1);
 		f->buf[0]='\0';
 		break;
 	case RD:
 	case END:
-		f->flags=0;
 		break;
 	case RDWR:
 	case WR:
+		f->rp=f->buf+f->bufl;
 		if(f->wp==f->rp){
-			if(f->flags&BALLOC)
-				f->buf=realloc(f->buf, f->bufl+1);
-			if(f->buf==NULL) return NULL;
+			if(f->flags&BALLOC){
+				char *t = realloc(f->buf, f->bufl+1);
+				if(t==NULL)
+					goto Error;
+				f->buf=t;
+				f->wp=t+f->bufl;
+			} else {
+				if(f->wp > f->buf)
+					*(f->wp-1) = '\0';
+				goto Error;
+			}
 		}
 		*f->wp='\0';
-		f->flags=0;
 		break;
 	}
 	f->state=CLOSED;

--
cinap