[Qemu-devel] [PATCH] Slirp reverse UDP firewall

* [Qemu-devel]  [PATCH] Slirp reverse UDP firewall
@ 2011-04-12 16:19 Daisuke Nojiri
  2011-04-12 16:38 ` Jan Kiszka
                   ` (2 more replies)
  0 siblings, 3 replies; 11+ messages in thread
From: Daisuke Nojiri @ 2011-04-12 16:19 UTC (permalink / raw)
  To: qemu-devel

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This patch adds: -drop-udp, -allow-udp ADDR:PORT, -drop-log FILE

  e.g.) $ qemu -net user -drop-log qemu.drop -drop-udp -allow-udp
10.0.2.3:53

-drop-udp enables usermode firewall for out-going UDP packats from a guest.
All UDP packets except ones allowed by -allow-udp will be dropped. Dropped
packets are logged in the file specified by FILE. PORT can be a single
number
(e.g. 53) or a range (e.g. [80-81]). If ADDR is ommitted, all addresses
match
the rule.

Signed-off-by: Daisuke Nojiri <dnojiri@google.com>

--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1119,6 +1119,24 @@ DEF("netdev", HAS_ARG, QEMU_OPTION_netdev,
     "vde|"
 #endif
     "socket],id=str[,option][,option][,...]\n", QEMU_ARCH_ALL)
+
+DEF("drop-udp", 0, QEMU_OPTION_drop_udp,
+"-drop-udp\tDrop UDP packets by usermode firewall\n",
+QEMU_ARCH_ALL)
+
+DEF("allow-udp", HAS_ARG, QEMU_OPTION_allow_udp,
+    "-allow-udp addr:port\n"
+    "                Add an allowed rule for -drop-udp. If destination
matches\n"
+    "                the rule, the packet won't be dropped. 'port' can be a
single\n"
+    "                number (e.g. 53) or a range (e.g. [80-81]. If 'addr'
is omitted,
+    "                all addresses match.\n",
+    QEMU_ARCH_ALL)
+
+DEF("drop-log", HAS_ARG, QEMU_OPTION_drop_log,
+    "-drop-log file\n"
+    "                Set usermode firewall log filename to 'file'.\n",
+    QEMU_ARCH_ALL)
+
 STEXI
 @item -net nic[,vlan=@var{n}][,macaddr=@var{mac}][,model=@var{type}]
[,name=@var{name}][,addr=@var{addr}][,vectors=@var{v}]
 @findex -net

diff --git a/slirp/libslirp.h b/slirp/libslirp.h
index 67c70e3..1ce5d68 100644
--- a/slirp/libslirp.h
+++ b/slirp/libslirp.h
@@ -44,6 +44,15 @@ void slirp_socket_recv(Slirp *slirp, struct in_addr
guest_addr,
 size_t slirp_socket_can_recv(Slirp *slirp, struct in_addr guest_addr,
                              int guest_port);

+/* Usermode firewall functions */
+void slirp_enable_drop_udp(void);
+void slirp_set_drop_log_fd(FILE *fd);
+void slirp_add_allow(const char *optarg, u_int8_t proto);
+int slirp_drop_log(const char *format, ...);
+int slirp_should_drop(unsigned long dst_addr,
+                      unsigned short dst_port,
+                      u_int8_t proto);
+
 #else /* !CONFIG_SLIRP */

 static inline void slirp_select_fill(int *pnfds, fd_set *readfds,
diff --git a/slirp/slirp.c b/slirp/slirp.c
index 1593be1..d321316 100644
--- a/slirp/slirp.c
+++ b/slirp/slirp.c
@@ -1111,3 +1111,192 @@ static int slirp_state_load(QEMUFile *f, void
*opaque, int version_id)

     return 0;
 }
+
+/*
+ * Allow rule for the usermode firewall
+ */
+struct ufw_allowed {
+    struct ufw_allowed *next;
+    unsigned long dst_addr;
+    /* Port range. For a single port, dst_lport = dst_hport. */
+    unsigned short dst_lport;   /* in host byte order */
+    unsigned short dst_hport;   /* in host byte order */
+};
+
+/*
+ * Global variables for the usermode firewall
+ */
+static int drop_udp = 0;
+static FILE *drop_log_fd = NULL;
+static struct ufw_allowed *fw_allowed_udp = NULL;
+
+void slirp_enable_drop_udp(void)
+{
+    drop_udp = 1;
+}
+
+void slirp_set_drop_log_fd(FILE *fd)
+{
+    drop_log_fd = fd;
+}
+
+int slirp_should_drop(unsigned long dst_addr,
+                      unsigned short dst_port,
+                      u_int8_t proto) {
+    struct ufw_allowed *fwa = NULL;
+    unsigned short dport;   /* host byte order */
+
+    switch (proto) {
+    case IPPROTO_UDP:
+        if (drop_udp == 0) {
+            return 0;
+        } else {
+            fwa = fw_allowed_udp;
+        }
+        break;
+    case IPPROTO_TCP:
+    default:
+        return 1;   /* unrecognized protocol. default drop. */
+    }
+
+    /* Find matching allow rule. 0 works as a wildcard for address. */
+    for (; fwa; fwa = fwa->next) {
+        dport = ntohs(dst_port);
+        if ((fwa->dst_lport <= dport) && (dport <= fwa->dst_hport)) {
+            /* allow any destination if 0 */
+            if (fwa->dst_addr == 0 || fwa->dst_addr == dst_addr) {
+                return 0;
+            }
+        }
+    }
+    return 1;
+}
+
+/*
+ * Register an allow rule for user mode firewall
+ */
+void slirp_add_allow_internal(unsigned long dst_addr,
+                              unsigned short dst_lport,
+                              unsigned short dst_hport,
+                              u_int8_t proto) {
+    struct ufw_allowed *fwa;
+
+    fwa = (struct ufw_allowed *)malloc(sizeof(struct ufw_allowed));
+    if (!fwa) {
+        DEBUG_MISC((dfd, "Unabled to create a new firewall rule "
+                    "due to malloc failure\n"));
+        exit(-1);
+    }
+
+    fwa->dst_addr = dst_addr;
+    fwa->dst_lport = dst_lport;
+    fwa->dst_hport = dst_hport;
+
+    switch (proto) {
+    case IPPROTO_UDP:
+        fwa->next = fw_allowed_udp;
+        fw_allowed_udp = fwa;
+        break;
+    case IPPROTO_TCP:
+    default:
+        free(fwa);
+        return;   /* unrecognized protocol */
+    }
+}
+
+/*
+ * Parse a null-terminated string specifying a network port or port range
(e.g.
+ * "[1024-65535]"). In case of a single port, lport and hport are the same.
+ * Returns 0 on success and -1 on error.
+ */
+int parse_port_range(const char *str,
+                     unsigned short *lport,
+                     unsigned short *hport) {
+    unsigned int low = 0, high = 0;
+    char *p, *arg = strdup(str);
+
+    p = rindex(arg, ']');
+    if ((*arg == '[') & (p != NULL)) {
+        p = arg + 1;   /* skip '[' */
+        low  = atoi(strsep(&p, "-"));
+        high = atoi(p);
+    } else {
+        low = atoi(arg);
+        high = low;
+    }
+
+    free(arg);
+
+    if ((low > 0) && (high > 0) && (low <= high) && (high < 65536)) {
+        *lport = low;
+        *hport = high;
+        return 0;
+    }
+
+    return -1;
+}
+
+/*
+ * Add allow rules for the usermode firewall.
+ */
+void slirp_add_allow(const char *optarg, u_int8_t proto)
+{
+    /*
+     * we expect the following format:
+     *  dst_addr:dst_port OR dst_addr:[dst_lport-dst_hport]
+     */
+    char *argument = strdup(optarg), *p = argument;
+    char *dst_addr_str, *dst_port_str;
+    struct in_addr dst_addr;
+    unsigned short dst_lport, dst_hport;
+
+    dst_addr_str = strsep(&p, ":");
+    dst_port_str = p;
+
+    if (dst_addr_str == NULL || dst_port_str == NULL) {
+        fprintf(stderr,
+                "Invalid argument %s for -allow. We expect "
+                "dst_addr:dst_port or dst_addr:[dst_lport-dst_hport]\n",
+                optarg);
+        exit(1);
+    }
+
+    /* handling ":port" notation (when IP address is omitted entirely). */
+    if (*dst_addr_str == '\0') {
+        dst_addr.s_addr = 0;
+    }
+    /* inet_aton returns 0 on failure. */
+    else if (inet_aton(dst_addr_str, &dst_addr) == 0) {
+        fprintf(stderr, "Invalid destination IP address: %s\n",
dst_addr_str);
+        exit(1);
+    }
+
+    if (parse_port_range(dst_port_str, &dst_lport, &dst_hport) == -1) {
+        fprintf(stderr, "Invalid destination port or port range\n");
+        exit(1);
+    }
+
+    slirp_add_allow_internal(dst_addr.s_addr, dst_lport, dst_hport, proto);
+
+    free(argument);
+}
+
+/*
+ * Write to drop-log
+ */
+int slirp_drop_log(const char *format, ...)
+{
+    va_list args;
+
+    if (!drop_log_fd) {
+        return 0;
 +    }
+
+    va_start(args, format);
+    vfprintf(drop_log_fd, format, args);
+    va_end(args);
+
+    fflush(drop_log_fd);
+
+    return 1;
+}
diff --git a/slirp/slirp.h b/slirp/slirp.h
index 954289a..29ee425 100644
--- a/slirp/slirp.h
+++ b/slirp/slirp.h
@@ -299,6 +299,15 @@ int tcp_emu(struct socket *, struct mbuf *);
 int tcp_ctl(struct socket *);
 struct tcpcb *tcp_drop(struct tcpcb *tp, int err);

+/* slirp.c */
+void slirp_add_allow_internal(unsigned long dst_addr,
+                              unsigned short dst_lport,
+                              unsigned short dst_hport,
+                              u_int8_t proto);
+int parse_port_range(const char *str,
+                     unsigned short *lport,
+                     unsigned short *hport);
+
 #ifdef USE_PPP
 #define MIN_MRU MINMRU
 #define MAX_MRU MAXMRU
diff --git a/slirp/udp.c b/slirp/udp.c
index 02b3793..db7e4ca 100644
--- a/slirp/udp.c
+++ b/slirp/udp.c
@@ -67,6 +67,8 @@ udp_input(register struct mbuf *m, int iphlen)
  DEBUG_ARG("m = %lx", (long)m);
  DEBUG_ARG("iphlen = %d", iphlen);

+        time_t timestamp = time(NULL);
+
  /*
  * Strip IP options, if any; should skip this,
  * make available to user, and use on returned packets,
@@ -98,6 +100,28 @@ udp_input(register struct mbuf *m, int iphlen)
  ip->ip_len = len;
  }

+        /*
+         * User mode firewall
+         */
+        if (slirp_should_drop(ip->ip_dst.s_addr, uh->uh_dport,
IPPROTO_UDP)) {
+            slirp_drop_log(
+                "Dropped UDP: src:0x%08x:0x%04hx dst:0x%08x:0x%04hx %ld\n",
+                ntohl(ip->ip_src.s_addr),
+                ntohs(uh->uh_sport),
+                ntohl(ip->ip_dst.s_addr),
+                ntohs(uh->uh_dport),
+                timestamp);
+            goto bad;
+        } else {
+            slirp_drop_log(
+                "Allowed UDP: src:0x%08x:0x%04hx dst:0x%08x:0x%04hx %ld\n",
+                ntohl(ip->ip_src.s_addr),
+                ntohs(uh->uh_sport),
+                ntohl(ip->ip_dst.s_addr),
+                ntohs(uh->uh_dport),
+                timestamp);
+        }
+
  /*
  * Save a copy of the IP header in case we want restore it
  * for sending an ICMP error message in response.
diff --git a/vl.c b/vl.c
index 68c3b53..b0583e3 100644
--- a/vl.c
+++ b/vl.c
@@ -2287,6 +2287,24 @@ int main(int argc, char **argv, char **envp)
                     exit(1);
                 break;
 #endif
+            case QEMU_OPTION_drop_udp:
+                slirp_enable_drop_udp();
+                break;
+            case QEMU_OPTION_allow_udp:
+                slirp_add_allow(optarg, IPPROTO_UDP);
+                break;
+            case QEMU_OPTION_drop_log:
+                {
+                    FILE *drop_log_fd;
+                    drop_log_fd = fopen(optarg, "w");
+
+                    if (!drop_log_fd) {
+                        fprintf(stderr, "Cannot open drop log: %s\n",
optarg);
+                        exit(1);
+                    }
+                    slirp_set_drop_log_fd(drop_log_fd);
+                }
+                break;
             case QEMU_OPTION_bt:
                 add_device_config(DEV_BT, optarg);
                 break;

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