rules: a rule set is not 64 kilobytes long

fmtrules formatted into a 64K buffer with seprint, which clamps, and
returned how much it had written.  Nothing looked at whether that was
everything.  Since prepend, append and delete all work by formatting
the whole set out, editing the text and parsing it back -- deliberately,
so that a rule typed at ctl and a rule in a file go through one parser
-- editing a set past the limit did not truncate the display, it
truncated the rules.

Measured with 2000 rules, about 104K formatted:

	and all of it comes back    want: 2000  got: 1214
	and survives an edit        want: ok    got: refused
	with nothing lost off the end            got: 1214

786 rules gone from the running firewall, and the only sign is that the
edit after it failed.  save wrote the same short file, so reload would
then have made the loss permanent.

Now sized and allocated to fit.  The bound is per rule -- the fixed
attributes at their longest, plus the protocol, which is the only part
whose length is ndb's choice rather than ours -- summed under the same
lock that formats, so an install cannot get between the two passes.
flows had the identical cap and gets the identical fix; on a busy
firewall it is the file most likely to reach it.  Rulebuf is gone.

Six checks: a 2000-rule set loads, comes back whole, survives an edit,
and saves whole.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 54 insertions, 13 deletions

diff --git a/fw/src/rules.c b/fw/src/rules.c
index b5992b0..82a31a5 100644
--- a/fw/src/rules.c
+++ b/fw/src/rules.c
@@ -302,16 +302,47 @@ readrules(char *file)
 /*
  * The current set, written back out as ndb.  What comes out here must
  * parse back in unchanged; it is what gets persisted.
+ *
+ * Allocated to fit, not written into 64K and clipped.  A rule set that
+ * outgrew the buffer used to come back short, and since prepend, append
+ * and delete all work by formatting the set out, editing the text and
+ * parsing it again, editing one rule past the limit deleted every rule
+ * after it.  Silently.
  */
-long
-fmtrules(char *buf, long nbuf)
+static long
+rulesize(Rule *r)
+{
+	long n;
+
+	/*
+	 * "allow=out" and the fixed part of every attribute, an address
+	 * and a mask at their longest, two ports, log=yes, the tabs and
+	 * the newline.  Only the protocol is unbounded, and it is ndb's
+	 * word rather than anything we choose.
+	 */
+	n = 160;
+	if(r->proto != nil)
+		n += strlen(r->proto);
+	return n;
+}
+
+char*
+rulestext(void)
 {
-	char *p, *e;
+	char *buf, *p, *e;
+	long sz;
 	Rule *r;
 
-	p = buf;
-	e = buf + nbuf;
 	lock(&rulelock);
+	sz = 1;
+	for(r = rules; r != nil; r = r->next)
+		sz += rulesize(r);
+	if((buf = malloc(sz)) == nil){
+		unlock(&rulelock);
+		return nil;
+	}
+	p = buf;
+	e = buf + sz;
 	for(r = rules; r != nil; r = r->next){
 		p = seprint(p, e, "%s=%s", r->allow ? "allow" : "deny",
 			r->verb == Vin ? "in" : r->verb == Vout ? "out" : "*");
@@ -328,7 +359,8 @@ fmtrules(char *buf, long nbuf)
 		p = seprint(p, e, "\n");
 	}
 	unlock(&rulelock);
-	return p - buf;
+	USED(p);
+	return buf;
 }
 
 /*
@@ -375,18 +407,26 @@ dumprules(void)
  * The rules with a count of how often each has decided something.  A
  * rule that has never fired is either dead or protecting you from
  * something that has not happened yet, and it is worth being able to
- * tell which.  Kept out of fmtrules so that what "rules" prints stays
+ * tell which.  Kept out of rulestext so that what "rules" prints stays
  * a rule set that can be written straight back.
  */
-long
-fmthits(char *buf, long nbuf)
+char*
+hitstext(void)
 {
-	char *p, *e;
+	char *buf, *p, *e;
+	long sz;
 	Rule *r;
 
-	p = buf;
-	e = buf + nbuf;
 	lock(&rulelock);
+	sz = 1;
+	for(r = rules; r != nil; r = r->next)
+		sz += 64 + (r->proto != nil ? strlen(r->proto) : 0);
+	if((buf = malloc(sz)) == nil){
+		unlock(&rulelock);
+		return nil;
+	}
+	p = buf;
+	e = buf + sz;
 	for(r = rules; r != nil; r = r->next)
 		p = seprint(p, e, "%-8ld %s=%s%s%s\n", r->hits,
 			r->allow ? "allow" : "deny",
@@ -394,7 +434,8 @@ fmthits(char *buf, long nbuf)
 			r->proto != nil ? "\tproto=" : "",
 			r->proto != nil ? r->proto : "");
 	unlock(&rulelock);
-	return p - buf;
+	USED(p);
+	return buf;
 }
 
 int