add disable_host_loopback (prohibit connections to 127.0.0.1)

From https://github.com/rootless-containers/slirp4netns/blob/4889f5299f407d7d7566c76a3b8b5f71c99b6db5/qemu_patches/0003-slirp-add-disable_host_loopback-prohibit-connections.patch

Original commits:
* https://github.com/rootless-containers/slirp4netns/commit/6325473781bb344c225f54e2d28800fb0619d7ee
* https://github.com/rootless-containers/slirp4netns/commit/13b24026867d4c30d5d1465ac82e3bb890bf4caa

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

7 files changed, 35 insertions, 13 deletions

diff --git a/src/ip_icmp.c b/src/ip_icmp.c
index 7590cff..58e35a5 100644
--- a/src/ip_icmp.c
+++ b/src/ip_icmp.c
@@ -190,7 +190,12 @@ void icmp_input(struct mbuf *m, int hlen)
 
             /* Send the packet */
             addr = so->fhost.ss;
-            sotranslate_out(so, &addr);
+            if (sotranslate_out(so, &addr) < 0) {
+                icmp_send_error(m, ICMP_UNREACH, ICMP_UNREACH_NET, 0,
+                                strerror(errno));
+                udp_detach(so);
+                return;
+            }
 
             if (sendto(so->s, icmp_ping_msg, strlen(icmp_ping_msg), 0,
                        (struct sockaddr *)&addr, sockaddr_size(&addr)) == -1) {
diff --git a/src/libslirp.h b/src/libslirp.h
index 2ba4388..a568488 100644
--- a/src/libslirp.h
+++ b/src/libslirp.h
@@ -89,6 +89,8 @@ typedef struct SlirpConfig {
     size_t if_mtu;
     /* Default: IF_MRU_DEFAULT */
     size_t if_mru;
+    /* Prohibit connecting to 127.0.0.1:* */
+    bool disable_host_loopback;
 } SlirpConfig;
 
 Slirp *slirp_new(const SlirpConfig *cfg, const SlirpCb *callbacks,
diff --git a/src/slirp.c b/src/slirp.c
index 3be982c..f645145 100644
--- a/src/slirp.c
+++ b/src/slirp.c
@@ -317,6 +317,7 @@ Slirp *slirp_new(const SlirpConfig *cfg, const SlirpCb *callbacks, void *opaque)
     }
     slirp->if_mtu = cfg->if_mtu == 0 ? IF_MTU_DEFAULT : cfg->if_mtu;
     slirp->if_mru = cfg->if_mru == 0 ? IF_MRU_DEFAULT : cfg->if_mru;
+    slirp->disable_host_loopback = cfg->disable_host_loopback;
 
     return slirp;
 }
diff --git a/src/slirp.h b/src/slirp.h
index 5fbee5c..ea8e8c5 100644
--- a/src/slirp.h
+++ b/src/slirp.h
@@ -147,6 +147,8 @@ struct Slirp {
     int if_mtu;
     int if_mru;
 
+    bool disable_host_loopback;
+
     /* mbuf states */
     struct quehead m_freelist;
     struct quehead m_usedlist;
diff --git a/src/socket.c b/src/socket.c
index 34daffc..d96d8c4 100644
--- a/src/socket.c
+++ b/src/socket.c
@@ -657,7 +657,9 @@ int sosendto(struct socket *so, struct mbuf *m)
 
     addr = so->fhost.ss;
     DEBUG_CALL(" sendto()ing)");
-    sotranslate_out(so, &addr);
+    if (sotranslate_out(so, &addr) < 0) {
+        return -1;
+    }
 
     /* Don't care what port we get */
     ret = sendto(so->s, m->m_data, m->m_len, 0, (struct sockaddr *)&addr,
@@ -818,8 +820,9 @@ void sofwdrain(struct socket *so)
 /*
  * Translate addr in host addr when it is a virtual address
  */
-void sotranslate_out(struct socket *so, struct sockaddr_storage *addr)
+int sotranslate_out(struct socket *so, struct sockaddr_storage *addr)
 {
+    int rc = 0;
     Slirp *slirp = so->slirp;
     struct sockaddr_in *sin = (struct sockaddr_in *)addr;
     struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *)addr;
@@ -830,18 +833,19 @@ void sotranslate_out(struct socket *so, struct sockaddr_storage *addr)
             slirp->vnetwork_addr.s_addr) {
             /* It's an alias */
             if (so->so_faddr.s_addr == slirp->vnameserver_addr.s_addr) {
-                if (get_dns_addr(&sin->sin_addr) < 0) {
-                    sin->sin_addr = loopback_addr;
+                if (get_dns_addr(&sin->sin_addr) >= 0) {
+                    goto ret;
                 }
+            }
+            if (slirp->disable_host_loopback) {
+                rc = -1;
+                errno = EPERM;
+                goto ret;
             } else {
                 sin->sin_addr = loopback_addr;
             }
         }
-
-        DEBUG_MISC(" addr.sin_port=%d, addr.sin_addr.s_addr=%.16s",
-                   ntohs(sin->sin_port), inet_ntoa(sin->sin_addr));
         break;
-
     case AF_INET6:
         if (in6_equal_net(&so->so_faddr6, &slirp->vprefix_addr6,
                           slirp->vprefix_len)) {
@@ -849,9 +853,13 @@ void sotranslate_out(struct socket *so, struct sockaddr_storage *addr)
                 uint32_t scope_id;
                 if (get_dns6_addr(&sin6->sin6_addr, &scope_id) >= 0) {
                     sin6->sin6_scope_id = scope_id;
-                } else {
-                    sin6->sin6_addr = in6addr_loopback;
+                    goto ret;
                 }
+            }
+            if (slirp->disable_host_loopback) {
+                rc = -1;
+                errno = EPERM;
+                goto ret;
             } else {
                 sin6->sin6_addr = in6addr_loopback;
             }
@@ -861,6 +869,8 @@ void sotranslate_out(struct socket *so, struct sockaddr_storage *addr)
     default:
         break;
     }
+ret:
+    return rc;
 }
 
 void sotranslate_in(struct socket *so, struct sockaddr_storage *addr)
diff --git a/src/socket.h b/src/socket.h
index d07f56d..a6a1e5e 100644
--- a/src/socket.h
+++ b/src/socket.h
@@ -155,7 +155,7 @@ struct iovec; /* For win32 */
 size_t sopreprbuf(struct socket *so, struct iovec *iov, int *np);
 int soreadbuf(struct socket *so, const char *buf, int size);
 
-void sotranslate_out(struct socket *, struct sockaddr_storage *);
+int sotranslate_out(struct socket *, struct sockaddr_storage *);
 void sotranslate_in(struct socket *, struct sockaddr_storage *);
 void sotranslate_accept(struct socket *);
 void sodrop(struct socket *, int num);
diff --git a/src/tcp_subr.c b/src/tcp_subr.c
index 83c7520..60cc0a1 100644
--- a/src/tcp_subr.c
+++ b/src/tcp_subr.c
@@ -424,7 +424,9 @@ int tcp_fconnect(struct socket *so, unsigned short af)
 
         addr = so->fhost.ss;
         DEBUG_CALL(" connect()ing");
-        sotranslate_out(so, &addr);
+        if (sotranslate_out(so, &addr) < 0) {
+            return -1;
+        }
 
         /* We don't care what port we get */
         ret = connect(s, (struct sockaddr *)&addr, sockaddr_size(&addr));