Allow resolv.conf be written by dhclient

When dhclient is used to assign and IP to the container,
it should be able to overwrite resolv.conf

Therefore, we do the /etc mirroring similarly to the situation with
manually configured nameservers.

When both DHCP and manually set nameservers are in use,
warn that the manual ones will be overwritten

2 files changed, 25 insertions, 3 deletions

diff --git a/src/firejail/firejail.h b/src/firejail/firejail.h
index a5eeb4067..bfe680d24 100644
--- a/src/firejail/firejail.h
+++ b/src/firejail/firejail.h
@@ -239,6 +239,24 @@ static inline int any_interface_configured(void) {
                 return 0;
 }
 
+static inline int any_ip_dhcp(void) {
+        if (cfg.bridge0.arg_ip_dhcp || cfg.bridge1.arg_ip_dhcp || cfg.bridge2.arg_ip_dhcp || cfg.bridge3.arg_ip_dhcp)
+                return 1;
+        else
+                return 0;
+}
+
+static inline int any_ip6_dhcp(void) {
+        if (cfg.bridge0.arg_ip6_dhcp || cfg.bridge1.arg_ip6_dhcp || cfg.bridge2.arg_ip6_dhcp || cfg.bridge3.arg_ip6_dhcp)
+                return 1;
+        else
+                return 0;
+}
+
+static inline int any_dhcp(void) {
+  return any_ip_dhcp() || any_ip6_dhcp();
+}
+
 extern int arg_private;         // mount private /home
 extern int arg_private_cache;   // private home/.cache
 extern int arg_debug;           // print debug messages
diff --git a/src/firejail/fs_hostname.c b/src/firejail/fs_hostname.c
index 9da01b24c..60c65746b 100644
--- a/src/firejail/fs_hostname.c
+++ b/src/firejail/fs_hostname.c
@@ -89,7 +89,7 @@ errexit:
 }
 
 void fs_resolvconf(void) {
-        if (cfg.dns1 == NULL)
+        if (cfg.dns1 == NULL && !any_dhcp())
                 return;
 
         if (arg_debug)
@@ -108,7 +108,8 @@ void fs_resolvconf(void) {
                 if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
                         continue;
                 // for resolv.conf we create a brand new file
-                if (strcmp(entry->d_name, "resolv.conf") == 0)
+                if (strcmp(entry->d_name, "resolv.conf") == 0 ||
+        strcmp(entry->d_name, "resolv.conf.dhclient-new") == 0)
                         continue;
 //              printf("linking %s\n", entry->d_name);
 
@@ -169,8 +170,11 @@ void fs_resolvconf(void) {
                 exit(1);
         }
 
-        if (cfg.dns1)
+        if (cfg.dns1) {
+    if (any_dhcp())
+      fwarning("network setup uses DHCP, nameservers will likely be overwritten\n");
                 fprintf(fp, "nameserver %s\n", cfg.dns1);
+  }
         if (cfg.dns2)
                 fprintf(fp, "nameserver %s\n", cfg.dns2);
         if (cfg.dns3)