libsec: improve thumbprint code

1) handle errors when loading thumbprint file.
initThumbprints() now returns nil and sets errstr
on error. a syntax error in a thumbprint file
should be reported instead of silently ignored!
(have to check users)

2) fix memory leak in initThumbprints(); we have to use
freeThumbprints() instead of free to release crltab.

3) use the actual head entries for thumbprint
storage in the thumbprints array. most thumbprint
files are rather sparse.

4) remove private emalloc() function. we shouldnt
just exit the calling process on allocation error,
instead handle error properly. this is a library!

Reference: /n/atom/patch/applied/improvethumb
Date: Sat Mar 15 16:55:52 CET 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/libsec/port/thumb.c	Sat Mar 15 16:53:33 2014
+++ /sys/src/libsec/port/thumb.c	Sat Mar 15 16:53:33 2014
@@ -7,26 +7,21 @@
 
 enum{ ThumbTab = 1<<10 };
 
-static void *
-emalloc(int n)
+static Thumbprint*
+tablehead(uchar *sum, Thumbprint *table)
 {
-	void *p;
-	if(n==0)
-		n=1;
-	p = malloc(n);
-	if(p == nil){
-		exits("out of memory");
-	}
-	memset(p, 0, n);
-	return p;
+	return &table[((sum[0]<<8) + sum[1]) & (ThumbTab-1)];
 }
 
 void
 freeThumbprints(Thumbprint *table)
 {
 	Thumbprint *hd, *p, *q;
+
+	if(table == nil)
+		return;
 	for(hd = table; hd < table+ThumbTab; hd++){
-		for(p = hd->next; p; p = q){
+		for(p = hd->next; p && p != hd; p = q){
 			q = p->next;
 			free(p);
 		}
@@ -37,61 +32,89 @@
 int
 okThumbprint(uchar *sum, Thumbprint *table)
 {
-	Thumbprint *p;
-	int i = ((sum[0]<<8) + sum[1]) & (ThumbTab-1);
+	Thumbprint *hd, *p;
 
-	for(p = table[i].next; p; p = p->next)
+	if(table == nil)
+		return 0;
+	hd = tablehead(sum, table);
+	for(p = hd->next; p; p = p->next){
 		if(memcmp(sum, p->sha1, SHA1dlen) == 0)
 			return 1;
+		if(p == hd)
+			break;
+	}
 	return 0;
 }
 
-static void
+static int
 loadThumbprints(char *file, Thumbprint *table, Thumbprint *crltab)
 {
-	Thumbprint *entry;
-	Biobuf *bin;
+	Thumbprint *hd, *entry;
 	char *line, *field[50];
 	uchar sum[SHA1dlen];
-	int i, r;
+	Biobuf *bin;
 
-	bin = Bopen(file, OREAD);
-	if(bin == nil)
-		return;
-	for(; (line = Brdstr(bin, '\n', 1)) != 0; free(line)){
+	if(access(file, AEXIST) < 0)
+		return 0;	/* not an error */
+	if((bin = Bopen(file, OREAD)) == nil)
+		return -1;
+	for(; (line = Brdstr(bin, '\n', 1)) != nil; free(line)){
 		if(tokenize(line, field, nelem(field)) < 2)
 			continue;
 		if(strcmp(field[0], "#include") == 0){
-			loadThumbprints(field[1], table, crltab);
+			if(loadThumbprints(field[1], table, crltab) < 0)
+				goto err;
 			continue;
 		}
-		if(strcmp(field[0], "x509") != 0 || strncmp(field[1], "sha1=", strlen("sha1=")) != 0)
+		if(strcmp(field[0], "x509") != 0 || strncmp(field[1], "sha1=", 5) != 0)
 			continue;
-		field[1] += strlen("sha1=");
-		r = dec16(sum, sizeof(sum), field[1], strlen(field[1]));
-		if(r == -1 || crltab && okThumbprint(sum, crltab))
+		field[1] += 5;
+		if(dec16(sum, SHA1dlen, field[1], strlen(field[1])) != SHA1dlen){
+			werrstr("malformed x509 entry in %s: %s", file, field[1]);
+			goto err;
+		}
+		if(crltab && okThumbprint(sum, crltab))
 			continue;
-		entry = (Thumbprint*)emalloc(sizeof(*entry));
+		hd = tablehead(sum, table);
+		if(hd->next == nil)
+			entry = hd;
+		else {
+			if((entry = malloc(sizeof(*entry))) == nil)
+				goto err;
+			entry->next = hd->next;
+		}
+		hd->next = entry;
 		memcpy(entry->sha1, sum, SHA1dlen);
-		i = ((sum[0]<<8) + sum[1]) & (ThumbTab-1);
-		entry->next = table[i].next;
-		table[i].next = entry;
 	}
 	Bterm(bin);
+	return 0;
+err:
+	free(line);
+	Bterm(bin);
+	return -1;
 }
 
 Thumbprint *
 initThumbprints(char *ok, char *crl)
 {
-	Thumbprint *table, *crltab = nil;
+	Thumbprint *table, *crltab;
 
+	table = crltab = nil;
 	if(crl){
-		crltab = emalloc(ThumbTab * sizeof(*table));
-		loadThumbprints(crl, crltab, nil);
+		if((crltab = malloc(ThumbTab * sizeof(*crltab))) == nil)
+			goto err;
+		memset(crltab, 0, ThumbTab * sizeof(*crltab));
+		if(loadThumbprints(crl, crltab, nil) < 0)
+			goto err;
+	}
+	if((table = malloc(ThumbTab * sizeof(*table))) == nil)
+		goto err;
+	memset(table, 0, ThumbTab * sizeof(*table));
+	if(loadThumbprints(ok, table, crltab) < 0){
+		freeThumbprints(table);
+		table = nil;
 	}
-	table = emalloc(ThumbTab * sizeof(*table));
-	loadThumbprints(ok, table, crltab);
-	free(crltab);
+err:
+	freeThumbprints(crltab);
 	return table;
 }
-