[Qemu-devel] [PATCH 06/10] slirp: Forward ICMP echo requests via unprivileged sockets

[Jan Kiszka]

Linux 3.0 gained support for unprivileged ICMP ping sockets. Use this
feature to forward guest pings to the outer world. The host admin has to
set the ping_group_range in order to grant access to those sockets. To
allow ping for the users group (GID 100):

echo 100 100 > /proc/sys/net/ipv4/ping_group_range

Signed-off-by: Jan Kiszka <address@hidden>
---
 slirp/ip_icmp.c  |   87 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
 slirp/ip_icmp.h  |    3 ++
 slirp/ip_input.c |    1 +
 slirp/misc.c     |   13 ++++++++
 slirp/slirp.c    |   37 +++++++++++++++++++++++
 slirp/slirp.h    |    5 +++
 slirp/socket.c   |    2 +
 7 files changed, 147 insertions(+), 1 deletions(-)

diff --git a/slirp/ip_icmp.c b/slirp/ip_icmp.c
index 4f10826..14a5312 100644
--- a/slirp/ip_icmp.c
+++ b/slirp/ip_icmp.c
@@ -60,6 +60,52 @@ static const int icmp_flush[19] = {
 /* ADDR MASK REPLY (18) */ 0
 };
 
+void icmp_init(Slirp *slirp)
+{
+    slirp->icmp.so_next = slirp->icmp.so_prev = &slirp->icmp;
+    slirp->icmp_last_so = &slirp->icmp;
+}
+
+static int icmp_send(struct socket *so, struct mbuf *m, int hlen)
+{
+    struct ip *ip = mtod(m, struct ip *);
+    struct sockaddr_in addr;
+
+    so->s = qemu_socket(AF_INET, SOCK_DGRAM, IPPROTO_ICMP);
+    if (so->s == -1) {
+        return -1;
+    }
+
+    so->so_m = m;
+    so->so_faddr = ip->ip_dst;
+    so->so_laddr = ip->ip_src;
+    so->so_iptos = ip->ip_tos;
+    so->so_type = IPPROTO_ICMP;
+    so->so_state = SS_ISFCONNECTED;
+    so->so_expire = curtime + SO_EXPIRE;
+
+    addr.sin_family = AF_INET;
+    addr.sin_addr = so->so_faddr;
+
+    insque(so, &so->slirp->icmp);
+
+    if (sendto(so->s, m->m_data + hlen, m->m_len - hlen, 0,
+               (struct sockaddr *)&addr, sizeof(addr)) == -1) {
+        DEBUG_MISC((dfd, "icmp_input icmp sendto tx errno = %d-%s\n",
+                    errno, strerror(errno)));
+        icmp_error(m, ICMP_UNREACH, ICMP_UNREACH_NET, 0, strerror(errno));
+        icmp_detach(so);
+    }
+
+    return 0;
+}
+
+void icmp_detach(struct socket *so)
+{
+    closesocket(so->s);
+    sofree(so);
+}
+
 /*
  * Process a received ICMP message.
  */
@@ -97,7 +143,6 @@ icmp_input(struct mbuf *m, int hlen)
   DEBUG_ARG("icmp_type = %d", icp->icmp_type);
   switch (icp->icmp_type) {
   case ICMP_ECHO:
-    icp->icmp_type = ICMP_ECHOREPLY;
     ip->ip_len += hlen;                     /* since ip_input subtracts this */
     if (ip->ip_dst.s_addr == slirp->vhost_addr.s_addr) {
       icmp_reflect(m);
@@ -107,6 +152,9 @@ icmp_input(struct mbuf *m, int hlen)
       struct socket *so;
       struct sockaddr_in addr;
       if ((so = socreate(slirp)) == NULL) goto freeit;
+      if (icmp_send(so, m, hlen) == 0) {
+        return;
+      }
       if(udp_attach(so) == -1) {
        DEBUG_MISC((dfd,"icmp_input udp_attach errno = %d-%s\n",
                    errno,strerror(errno)));
@@ -321,6 +369,7 @@ icmp_reflect(struct mbuf *m)
   m->m_len -= hlen;
   icp = mtod(m, struct icmp *);
 
+  icp->icmp_type = ICMP_ECHOREPLY;
   icp->icmp_cksum = 0;
   icp->icmp_cksum = cksum(m, ip->ip_len - hlen);
 
@@ -351,3 +400,39 @@ icmp_reflect(struct mbuf *m)
 
   (void ) ip_output((struct socket *)NULL, m);
 }
+
+void icmp_receive(struct socket *so)
+{
+    struct mbuf *m = so->so_m;
+    struct ip *ip = mtod(m, struct ip *);
+    int hlen = ip->ip_hl << 2;
+    u_char error_code;
+    struct icmp *icp;
+    int id, len;
+
+    m->m_data += hlen;
+    m->m_len -= hlen;
+    icp = mtod(m, struct icmp *);
+
+    id = icp->icmp_id;
+    len = recv(so->s, icp, m->m_len, 0);
+    icp->icmp_id = id;
+
+    m->m_data -= hlen;
+    m->m_len += hlen;
+
+    if (len == -1 || len == 0) {
+        if (errno == ENETUNREACH) {
+            error_code = ICMP_UNREACH_NET;
+        } else {
+            error_code = ICMP_UNREACH_HOST;
+        }
+        DEBUG_MISC((dfd, " udp icmp rx errno = %d-%s\n", errno,
+                    strerror(errno)));
+        icmp_error(so->so_m, ICMP_UNREACH, error_code, 0, strerror(errno));
+    } else {
+        icmp_reflect(so->so_m);
+        so->so_m = NULL; /* Don't m_free() it again! */
+    }
+    icmp_detach(so);
+}
diff --git a/slirp/ip_icmp.h b/slirp/ip_icmp.h
index 2692822..b3da1f2 100644
--- a/slirp/ip_icmp.h
+++ b/slirp/ip_icmp.h
@@ -153,9 +153,12 @@ struct icmp {
        (type) == ICMP_IREQ || (type) == ICMP_IREQREPLY || \
        (type) == ICMP_MASKREQ || (type) == ICMP_MASKREPLY)
 
+void icmp_init(Slirp *slirp);
 void icmp_input(struct mbuf *, int);
 void icmp_error(struct mbuf *msrc, u_char type, u_char code, int minsize,
                 const char *message);
 void icmp_reflect(struct mbuf *);
+void icmp_receive(struct socket *so);
+void icmp_detach(struct socket *so);
 
 #endif
diff --git a/slirp/ip_input.c b/slirp/ip_input.c
index 46c60b0..5e67631 100644
--- a/slirp/ip_input.c
+++ b/slirp/ip_input.c
@@ -58,6 +58,7 @@ ip_init(Slirp *slirp)
     slirp->ipq.ip_link.next = slirp->ipq.ip_link.prev = &slirp->ipq.ip_link;
     udp_init(slirp);
     tcp_init(slirp);
+    icmp_init(slirp);
 }
 
 /*
diff --git a/slirp/misc.c b/slirp/misc.c
index 34179e2..6002550 100644
--- a/slirp/misc.c
+++ b/slirp/misc.c
@@ -407,4 +407,17 @@ void slirp_connection_info(Slirp *slirp, Monitor *mon)
                        inet_ntoa(dst_addr), ntohs(dst_port),
                        so->so_rcv.sb_cc, so->so_snd.sb_cc);
     }
+
+    for (so = slirp->icmp.so_next; so != &slirp->icmp; so = so->so_next) {
+        n = snprintf(buf, sizeof(buf), "  ICMP[%d sec]",
+                     (so->so_expire - curtime) / 1000);
+        src.sin_addr = so->so_laddr;
+        dst_addr = so->so_faddr;
+        memset(&buf[n], ' ', 19 - n);
+        buf[19] = 0;
+        monitor_printf(mon, "%s %3d %15s  -    ", buf, so->s,
+                       src.sin_addr.s_addr ? inet_ntoa(src.sin_addr) : "*");
+        monitor_printf(mon, "%15s  -    %5d %5d\n", inet_ntoa(dst_addr),
+                       so->so_rcv.sb_cc, so->so_snd.sb_cc);
+    }
 }
diff --git a/slirp/slirp.c b/slirp/slirp.c
index 1593be1..faaa2f3 100644
--- a/slirp/slirp.c
+++ b/slirp/slirp.c
@@ -373,6 +373,31 @@ void slirp_select_fill(int *pnfds,
                                UPD_NFDS(so->s);
                        }
                }
+
+                /*
+                 * ICMP sockets
+                 */
+                for (so = slirp->icmp.so_next; so != &slirp->icmp;
+                     so = so_next) {
+                    so_next = so->so_next;
+
+                    /*
+                     * See if it's timed out
+                     */
+                    if (so->so_expire) {
+                        if (so->so_expire <= curtime) {
+                            icmp_detach(so);
+                            continue;
+                        } else {
+                            do_slowtimo = 1; /* Let socket expire */
+                        }
+                    }
+
+                    if (so->so_state & SS_ISFCONNECTED) {
+                        FD_SET(so->s, readfds);
+                        UPD_NFDS(so->s);
+                    }
+                }
        }
 
         *pnfds = nfds;
@@ -542,6 +567,18 @@ void slirp_select_poll(fd_set *readfds, fd_set *writefds, 
fd_set *xfds,
                             sorecvfrom(so);
                         }
                }
+
+                /*
+                 * Check incoming ICMP relies.
+                 */
+                for (so = slirp->icmp.so_next; so != &slirp->icmp;
+                     so = so_next) {
+                     so_next = so->so_next;
+
+                    if (so->s != -1 && FD_ISSET(so->s, readfds)) {
+                        icmp_receive(so);
+                    }
+                }
        }
 
        /*
diff --git a/slirp/slirp.h b/slirp/slirp.h
index 954289a..16bb6ba 100644
--- a/slirp/slirp.h
+++ b/slirp/slirp.h
@@ -152,6 +152,7 @@ int inet_aton(const char *cp, struct in_addr *ia);
 #include "tcp_var.h"
 #include "tcpip.h"
 #include "udp.h"
+#include "ip_icmp.h"
 #include "mbuf.h"
 #include "sbuf.h"
 #include "socket.h"
@@ -218,6 +219,10 @@ struct Slirp {
     struct socket udb;
     struct socket *udp_last_so;
 
+    /* icmp states */
+    struct socket icmp;
+    struct socket *icmp_last_so;
+
     /* tftp states */
     char *tftp_prefix;
     struct tftp_session tftp_sessions[TFTP_SESSIONS_MAX];
diff --git a/slirp/socket.c b/slirp/socket.c
index 6119234..9b8ae13 100644
--- a/slirp/socket.c
+++ b/slirp/socket.c
@@ -71,6 +71,8 @@ sofree(struct socket *so)
       slirp->tcp_last_so = &slirp->tcb;
   } else if (so == slirp->udp_last_so) {
       slirp->udp_last_so = &slirp->udb;
+  } else if (so == slirp->icmp_last_so) {
+      slirp->icmp_last_so = &slirp->icmp;
   }
   m_free(so->so_m);
 
-- 
1.7.3.4