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Diffstat (limited to 'fw/src')
-rw-r--r--fw/src/ether.c24
-rw-r--r--fw/src/fw.c89
-rw-r--r--fw/src/netfs.c67
-rw-r--r--fw/src/rules.c36
4 files changed, 173 insertions, 43 deletions
diff --git a/fw/src/ether.c b/fw/src/ether.c
index 54f5068..dd20971 100644
--- a/fw/src/ether.c
+++ b/fw/src/ether.c
@@ -38,6 +38,7 @@ enum
Arplen = 28,
Eminlen = 60, /* ethernet minimum frame, devether enforces it */
+ Maxframe = Ehdrlen + 16*1024,
Arpreq = 1,
Arpreply = 2,
@@ -323,11 +324,16 @@ etherisip(uchar *f, int n)
int
etherwriteip(uchar *p, int n, uchar *mask)
{
- uchar f[Ehdrlen + 64*1024], dst[IPaddrlen], hop[IPaddrlen];
+ /*
+ * On a proc stack, which libthread keeps small: 64K here
+ * overran it and corrupted the data segment. pktmedium's maxtu
+ * is 4096, so this is already generous.
+ */
+ uchar f[Maxframe], dst[IPaddrlen], hop[IPaddrlen];
uchar net[IPaddrlen], ournet[IPaddrlen], mac[Eaddrlen];
int type, len;
- if(n < 20 || n > 64*1024 - Ehdrlen)
+ if(n < 20 || n > Maxframe - Ehdrlen)
return -1;
switch(p[0] >> 4){
case 4:
@@ -355,6 +361,20 @@ etherwriteip(uchar *p, int n, uchar *mask)
ipmove(hop, dst);
if(!arpget(hop, mac)){
+ /*
+ * v6 has no ARP; resolving a neighbour needs ICMPv6
+ * solicitation, which is not implemented. Say so once,
+ * rather than dropping every v6 unicast in silence.
+ */
+ if(!isv4(hop)){
+ static int said;
+
+ if(!said++)
+ fprint(2, "fw: cannot resolve %I: "
+ "IPv6 neighbour discovery is not implemented, "
+ "so v6 unicast is dropped\n", hop);
+ return -1;
+ }
if(etherdebug)
fprint(2, "arp: no entry for %I, dropping and asking\n", hop);
arpask(hop);
diff --git a/fw/src/fw.c b/fw/src/fw.c
index 4f94090..a136194 100644
--- a/fw/src/fw.c
+++ b/fw/src/fw.c
@@ -48,6 +48,7 @@ struct Pkt
uchar dst[IPaddrlen];
int sport;
int dport;
+ int frag; /* a later fragment: no ports in it */
int verb;
};
@@ -130,6 +131,15 @@ flowlook(int proto, uchar *src, uchar *dst, int sport, int dport, long now)
h = flowhash(proto, src, dst, sport, dport);
for(f = flowtab[h]; f != nil; f = f->next)
if(flowis(f, proto, src, dst, sport, dport)){
+ /*
+ * An expired flow must not match. Reaping only
+ * happens when a flow is added, so on a quiet
+ * firewall nothing is ever reaped and a flow that
+ * timed out long ago would keep passing traffic,
+ * refreshing itself on every packet.
+ */
+ if(now - f->last > flowtimeout(f->proto))
+ return 0;
f->last = now;
return 1;
}
@@ -295,6 +305,13 @@ wireup(Wire *w)
if(fprint(w->cfd, "bind pkt") < 0)
sysfatal("%s: bind pkt: %r", w->net);
+ /*
+ * pktmedium claims 4096 with no link header; a card is 1514 with
+ * 14. Left alone the protected stack emits packets the card
+ * refuses, and only remote peers capping the MSS hide it.
+ */
+ if(fprint(w->cfd, "mtu 1500") < 0)
+ fprint(2, "fw: %s: cannot set mtu: %r\n", w->net);
if(fprint(w->cfd, "add %s %s", w->addr, w->mask) < 0)
sysfatal("%s: add %s %s: %r", w->net, w->addr, w->mask);
@@ -333,6 +350,15 @@ parsepkt(uchar *b, int n, Pkt *p)
p->proto = b[9];
v4tov6(p->src, b + 12);
v4tov6(p->dst, b + 16);
+ /*
+ * Only the first fragment carries the transport header.
+ * Reading one out of a later fragment gives payload bytes
+ * as ports, which both loses the traffic - it matches no
+ * flow - and lets a crafted fragment whose bytes happen to
+ * match an open flow through.
+ */
+ if((nhgets(b + 6) & 0x1FFF) != 0)
+ p->frag = 1;
t = b + hl;
n -= hl;
break;
@@ -349,7 +375,7 @@ parsepkt(uchar *b, int n, Pkt *p)
return;
}
- if((p->proto == 6 || p->proto == 17) && n >= 4){
+ if(!p->frag && (p->proto == 6 || p->proto == 17) && n >= 4){
p->sport = nhgets(t);
p->dport = nhgets(t + 2);
}
@@ -382,7 +408,7 @@ relay(Wire *from, Wire *to, int verb)
if((n = read(from->dfd, buf, Maxpkt)) <= 0){
fprint(2, "fw: %s: read failed: %r\n", from->side);
syslog(0, "fw", "%s: read failed: %r", from->side);
- return;
+ threadexitsall("wire");
}
parsepkt(buf, n, &p);
@@ -818,8 +844,15 @@ fswrite(Req *r)
err = editrules(arg, 1, 0);
else if(strcmp(buf, "append") == 0)
err = editrules(arg, 0, 0);
- else if(strcmp(buf, "delete") == 0)
- err = editrules(nil, 0, atoi(arg));
+ else if(strcmp(buf, "delete") == 0){
+ int nr;
+
+ nr = atoi(arg);
+ if(nr < 1)
+ err = "delete wants a rule number, from 1";
+ else
+ err = editrules(nil, 0, nr);
+ }
else
err = "unknown command; read ctl for the list";
@@ -854,14 +887,21 @@ rulesdidchange(void)
static void
servectl(char *mtpt, char *srvname)
{
+ char *user;
File *root;
- fs.tree = alloctree("fw", "fw", DMDIR|0555, nil);
+ /*
+ * Owned by whoever is running fw, not by a user called "fw" that
+ * does not exist: with 0600 that locked out the administrator as
+ * effectively as everyone else.
+ */
+ user = getuser();
+ fs.tree = alloctree(user, user, DMDIR|0555, nil);
root = fs.tree->root;
- closefile(createfile(root, "ctl", "fw", 0666, (void*)Qctl));
- closefile(createfile(root, "rules", "fw", 0666, (void*)Qrules));
- closefile(createfile(root, "flows", "fw", 0444, (void*)Qflows));
- closefile(createfile(root, "stats", "fw", 0444, (void*)Qstats));
+ closefile(createfile(root, "ctl", user, 0600, (void*)Qctl));
+ closefile(createfile(root, "rules", user, 0600, (void*)Qrules));
+ closefile(createfile(root, "flows", user, 0440, (void*)Qflows));
+ closefile(createfile(root, "stats", user, 0440, (void*)Qstats));
threadpostmountsrv(&fs, srvname, mtpt, MREPL);
}
@@ -947,9 +987,14 @@ etherin(void *a)
buf = emalloc(Maxpkt);
for(;;){
if((n = read(efd, buf, Maxpkt)) <= 0){
+ /*
+ * One relay stopping would leave the other running
+ * and that direction unfiltered, with nothing to
+ * notice. Take the whole firewall down instead.
+ */
fprint(2, "fw: %s: read the card: %r\n", w->side);
syslog(0, "fw", "stopped reading the card: %r");
- return;
+ threadexitsall("card");
}
if(debug > 1)
fprint(2, "wire: %d bytes type %.4ux\n", n, (buf[12]<<8)|buf[13]);
@@ -977,7 +1022,7 @@ etherout(void *a)
if((n = read(w->dfd, buf, Maxpkt)) <= 0){
fprint(2, "fw: %s: read the stack: %r\n", w->side);
syslog(0, "fw", "stopped reading the stack: %r");
- return;
+ threadexitsall("stack");
}
if(permitted(buf, n, Vout, &p))
etherwriteip(buf, n, ethermask);
@@ -1057,6 +1102,19 @@ learnaddr(char *net, char *dev, char *addr, int naddr, char *gw, int ngw)
* it: a live fw would still be holding the card we are about to take.
*/
/*
+ * Undo a previous fw that died.
+ *
+ * An IP stack outlives the program that configured it, so a fw that is
+ * killed leaves its pkt interface behind, holding the address, with
+ * nothing on the other end of it. The machine has no network until
+ * someone unpicks that by hand, and the next fw to start makes a second
+ * interface with the same address and routes that could go to either.
+ *
+ * So before taking anything, throw away any pkt interface already
+ * carrying the address we are about to use. Nothing else can have made
+ * it: a live fw would still be holding the card we are about to take.
+ */
+/*
* Put the card back.
*
* Taking a card is destructive: the stack loses it, and the pkt
@@ -1248,6 +1306,7 @@ threadmain(int argc, char **argv)
fmtinstall('I', eipfmt);
fmtinstall('V', eipfmt);
fmtinstall('E', eipfmt);
+ fmtinstall('M', eipfmt); /* fmtrules prints masks with it */
rulepath = argv[0];
readrules(rulepath);
@@ -1317,14 +1376,6 @@ threadmain(int argc, char **argv)
ethersetaddr(ip, gw, haveg);
reclaim(netmtpt, abuf);
- backdev = etherdev;
- backaddr = abuf;
- backmask = m;
- backnet = netmtpt;
- backgw = ethergw;
- atexit(putback);
- threadnotify(notehandler, 1);
-
takecard(netmtpt, etherdev);
prot = emalloc(sizeof *prot);
diff --git a/fw/src/netfs.c b/fw/src/netfs.c
index c87412d..f28485f 100644
--- a/fw/src/netfs.c
+++ b/fw/src/netfs.c
@@ -121,11 +121,31 @@ hidden(char *path)
static char*
protect(char *path, int mode)
{
+ char *p;
+
if(hidden(path))
return "fw: does not exist";
if(strcmp(path, "ipifc/clone") == 0)
return "fw: interface creation denied";
- if(under(path, "ipifc") || under(path, "iproute") || under(path, "arp"))
+
+ /*
+ * An interface's data file is a wire. On a machine that is also
+ * running fw -e it is *the* wire, so reading it hands a filtered
+ * program the packet stream the filter exists to control. Not
+ * read-only: not at all.
+ */
+ if(under(path, "ipifc"))
+ if((p = strrchr(path, '/')) != nil && strcmp(p+1, "data") == 0)
+ return "fw: denied";
+
+ /*
+ * ndb is the machine's configuration and log is a trace of every
+ * connection on it, both mode 0666. Writing the first
+ * reconfigures name service for everyone; reading the second
+ * after enabling it watches the whole machine.
+ */
+ if(under(path, "ipifc") || under(path, "iproute") || under(path, "arp")
+ || under(path, "ndb") || under(path, "log"))
if((mode & 3) != OREAD)
return "fw: read-only under fw";
return nil;
@@ -181,6 +201,22 @@ ctlproto(char *path)
* connect takes addr!port with optional trailing fields; announce takes
* a bare port, or addr!port with addr often "*".
*/
+/*
+ * Control messages that only change how this one conversation behaves,
+ * and so cannot reach the network by themselves. Everything outside
+ * this list is refused: see checkctl.
+ */
+static char *okverbs[] = {
+ "bind", /* the local address; announce is what opens */
+ "ttl",
+ "tos",
+ "ignoreadvice",
+ "close",
+ "hangup",
+ "keepalive",
+ nil,
+};
+
static char*
checkctl(char *proto, char *msg, long n)
{
@@ -188,7 +224,7 @@ checkctl(char *proto, char *msg, long n)
static char err[128];
uchar ip[IPaddrlen], mask[IPaddrlen];
Rule *rule;
- int nf, na, verb, anyip, port, lport;
+ int nf, na, verb, anyip, port, lport, i;
if(n <= 0)
return nil;
@@ -203,8 +239,31 @@ checkctl(char *proto, char *msg, long n)
verb = Vout;
else if(strcmp(f[0], "announce") == 0)
verb = Vin;
- else
- return nil; /* hangup, ttl, keepalive: not policy */
+ else{
+ /*
+ * Anything else is refused unless it is known to be
+ * harmless. Letting unknown control messages through was
+ * a hole, not a convenience: "headers" on a udp
+ * conversation turns it into one that carries its own
+ * destination, and the write queue is live from the
+ * moment it is cloned, so three writes send a datagram
+ * anywhere with no connect for a rule to match. gre has
+ * "raw" and "forward"; rudp and icmpv6 have "headers"
+ * too.
+ *
+ * This is the same argument the rule parser already makes
+ * about attributes it does not recognise, applied to the
+ * place it was not.
+ */
+ for(i = 0; okverbs[i] != nil; i++)
+ if(strcmp(f[0], okverbs[i]) == 0)
+ return nil;
+ syslog(0, "fw", "deny %s %s: control message not permitted",
+ proto, f[0]);
+ snprint(err, sizeof err,
+ "fw: %s: not a permitted control message", f[0]);
+ return err;
+ }
if(nf < 2)
return nil; /* malformed; let the kernel say so */
diff --git a/fw/src/rules.c b/fw/src/rules.c
index c0df82d..55de9cb 100644
--- a/fw/src/rules.c
+++ b/fw/src/rules.c
@@ -30,7 +30,6 @@ Rule *rules;
void (*rulechanged)(void);
static Lock rulelock;
-static Rule *lastrule;
static char *rulefile;
static char *parseerr;
static jmp_buf parsejmp;
@@ -135,7 +134,7 @@ verbof(char *s)
* a firewall gets to do.
*/
static void
-addrule(Ndbtuple *t, int nr)
+addrule(Ndbtuple *t, int nr, Rule **head, Rule **tail)
{
char *ip, *mask, *p, abuf[64];
Rule *r;
@@ -206,28 +205,34 @@ addrule(Ndbtuple *t, int nr)
r->anyip = 0;
}
- if(lastrule == nil)
- rules = r;
+ if(*head == nil)
+ *head = r;
else
- lastrule->next = r;
- lastrule = r;
+ (*tail)->next = r;
+ *tail = r;
}
/*
* Parse without installing. Returns the new list, or nil with *err set.
* An empty file is a valid rule set: it denies everything.
*/
+/*
+ * Build the new list in locals. Earlier this borrowed the globals and
+ * put them back afterwards, which meant that for the length of a reload
+ * the relay procs - which take rulelock, a lock this never held - were
+ * walking a list that was first empty and then half built. Every packet
+ * in that window was judged against a partial rule set, and a parse
+ * failure freed nodes a relay might still have been holding.
+ */
Rule*
parserules(char *file, char **err)
{
- Rule *new, *save, *savelast;
+ Rule *head, *tail;
Ndbtuple *t;
Ndb *db;
int nr;
- save = rules;
- savelast = lastrule;
- rules = lastrule = nil;
+ head = tail = nil;
rulefile = file;
parseerr = nil;
@@ -236,30 +241,25 @@ parserules(char *file, char **err)
snprint(eb, sizeof eb, "%s: %r", file);
*err = eb;
- rules = save;
- lastrule = savelast;
return nil;
}
parsing = 1;
if(setjmp(parsejmp) == 0){
for(nr = 1; (t = ndbparse(db)) != nil; nr++){
- addrule(t, nr);
+ addrule(t, nr, &head, &tail);
ndbfree(t);
}
}
parsing = 0;
ndbclose(db);
- new = rules;
- rules = save;
- lastrule = savelast;
if(parseerr != nil){
- freerules(new);
+ freerules(head);
*err = parseerr;
return nil;
}
*err = nil;
- return new;
+ return head;
}
void
generated by cgit v1.2.3 (git 2.39.1) at 2026-08-23 02:10:15 +0000