nss-resolve: fallback to the class NSS "dns" module if we cannot contact resolved

[elogind.git] / src / nss-resolve / nss-resolve.c

diff --git a/src/nss-resolve/nss-resolve.c b/src/nss-resolve/nss-resolve.c
index 0dbc224b5c12af31eb61cd84897c986248719271..b2cb19a7b42918afd2dbb21ed50ecf88352d5156 100644 (file)
--- a/src/nss-resolve/nss-resolve.c
+++ b/src/nss-resolve/nss-resolve.c
@@ -29,6 +29,7 @@
 #include <net/if.h>
 #include <stdlib.h>
 #include <arpa/inet.h>
+#include <dlfcn.h>
 
 #include "sd-bus.h"
 #include "bus-util.h"
@@ -43,20 +44,41 @@ NSS_GETHOSTBYADDR_PROTOTYPES(resolve);
 
 #define DNS_CALL_TIMEOUT_USEC (45*USEC_PER_SEC)
 
-static int count_addresses(sd_bus_message *m, unsigned af, const char **canonical) {
+typedef void (*voidfunc_t)(void);
+
+static voidfunc_t find_fallback(const char *module, const char *symbol) {
+        void *dl;
+
+        /* Try to find a fallback NSS module symbol */
+
+        dl = dlopen(module, RTLD_LAZY|RTLD_NODELETE);
+        if (!dl)
+                return NULL;
+
+        return dlsym(dl, symbol);
+}
+
+static bool bus_error_shall_fallback(sd_bus_error *e) {
+        return sd_bus_error_has_name(e, SD_BUS_ERROR_SERVICE_UNKNOWN) ||
+               sd_bus_error_has_name(e, SD_BUS_ERROR_NAME_HAS_NO_OWNER) ||
+               sd_bus_error_has_name(e, SD_BUS_ERROR_NO_REPLY) ||
+               sd_bus_error_has_name(e, SD_BUS_ERROR_ACCESS_DENIED);
+}
+
+static int count_addresses(sd_bus_message *m, int af, const char **canonical) {
         int c = 0, r;
 
         assert(m);
         assert(canonical);
 
-        r = sd_bus_message_enter_container(m, 'a', "(yayi)");
+        r = sd_bus_message_enter_container(m, 'a', "(iayi)");
         if (r < 0)
                 return r;
 
-        while ((r = sd_bus_message_enter_container(m, 'r', "yayi")) > 0) {
-                unsigned char family;
+        while ((r = sd_bus_message_enter_container(m, 'r', "iayi")) > 0) {
+                int family;
 
-                r = sd_bus_message_read(m, "y", &family);
+                r = sd_bus_message_read(m, "i", &family);
                 if (r < 0)
                         return r;
 
@@ -131,7 +153,7 @@ enum nss_status _nss_resolve_gethostbyname4_r(
         if (r < 0)
                 goto fail;
 
-        r = sd_bus_message_append(req, "sy", name, AF_UNSPEC);
+        r = sd_bus_message_append(req, "si", name, AF_UNSPEC);
         if (r < 0)
                 goto fail;
 
@@ -143,6 +165,25 @@ enum nss_status _nss_resolve_gethostbyname4_r(
                         return NSS_STATUS_NOTFOUND;
                 }
 
+                if (bus_error_shall_fallback(&error)) {
+
+                        enum nss_status (*fallback)(
+                                        const char *name,
+                                        struct gaih_addrtuple **pat,
+                                        char *buffer, size_t buflen,
+                                        int *errnop, int *h_errnop,
+                                        int32_t *ttlp);
+
+                        fallback = (enum nss_status (*)(const char *name,
+                                                        struct gaih_addrtuple **pat,
+                                                        char *buffer, size_t buflen,
+                                                        int *errnop, int *h_errnop,
+                                                        int32_t *ttlp))
+                                find_fallback("libnss_dns.so.2", "_nss_dns_gethostbyname4_r");
+                        if (fallback)
+                                return fallback(name, pat, buffer, buflen, errnop, h_errnop, ttlp);
+                }
+
                 *errnop = -r;
                 *h_errnop = NO_RECOVERY;
                 return NSS_STATUS_UNAVAIL;
@@ -178,17 +219,16 @@ enum nss_status _nss_resolve_gethostbyname4_r(
         /* Second, append addresses */
         r_tuple_first = (struct gaih_addrtuple*) (buffer + idx);
 
-        r = sd_bus_message_enter_container(reply, 'a', "(yayi)");
+        r = sd_bus_message_enter_container(reply, 'a', "(iayi)");
         if (r < 0)
                 goto fail;
 
-        while ((r = sd_bus_message_enter_container(reply, 'r', "yayi")) > 0) {
-                unsigned char family;
+        while ((r = sd_bus_message_enter_container(reply, 'r', "iayi")) > 0) {
+                int family, ifindex;
                 const void *a;
-                int ifindex;
                 size_t sz;
 
-                r = sd_bus_message_read(reply, "y", &family);
+                r = sd_bus_message_read(reply, "i", &family);
                 if (r < 0)
                         goto fail;
 
@@ -207,7 +247,7 @@ enum nss_status _nss_resolve_gethostbyname4_r(
                 if (!IN_SET(family, AF_INET, AF_INET6))
                         continue;
 
-                if (sz != PROTO_ADDRESS_SIZE(family)) {
+                if (sz != FAMILY_ADDRESS_SIZE(family)) {
                         r = -EINVAL;
                         goto fail;
                 }
@@ -298,7 +338,7 @@ enum nss_status _nss_resolve_gethostbyname3_r(
         if (r < 0)
                 goto fail;
 
-        r = sd_bus_message_append(req, "sy", name, af);
+        r = sd_bus_message_append(req, "si", name, af);
         if (r < 0)
                 goto fail;
 
@@ -310,6 +350,29 @@ enum nss_status _nss_resolve_gethostbyname3_r(
                         return NSS_STATUS_NOTFOUND;
                 }
 
+                if (bus_error_shall_fallback(&error)) {
+
+                        enum nss_status (*fallback)(
+                                        const char *name,
+                                        int af,
+                                        struct hostent *result,
+                                        char *buffer, size_t buflen,
+                                        int *errnop, int *h_errnop,
+                                        int32_t *ttlp,
+                                        char **canonp);
+
+                        fallback =  (enum nss_status (*)(const char *name,
+                                                         int af,
+                                                         struct hostent *result,
+                                                         char *buffer, size_t buflen,
+                                                         int *errnop, int *h_errnop,
+                                                         int32_t *ttlp,
+                                                         char **canonp))
+                                find_fallback("libnss_dns.so.2", "_nss_dns_gethostbyname3_r");
+                        if (fallback)
+                                return fallback(name, af, result, buffer, buflen, errnop, h_errnop, ttlp, canonp);
+                }
+
                 *errnop = -r;
                 *h_errnop = NO_RECOVERY;
                 return NSS_STATUS_UNAVAIL;
@@ -329,7 +392,7 @@ enum nss_status _nss_resolve_gethostbyname3_r(
         if (isempty(canonical))
                 canonical = name;
 
-        alen = PROTO_ADDRESS_SIZE(af);
+        alen = FAMILY_ADDRESS_SIZE(af);
         l = strlen(canonical);
 
         ms = ALIGN(l+1) +
@@ -356,17 +419,16 @@ enum nss_status _nss_resolve_gethostbyname3_r(
         /* Third, append addresses */
         r_addr = buffer + idx;
 
-        r = sd_bus_message_enter_container(reply, 'a', "(yayi)");
+        r = sd_bus_message_enter_container(reply, 'a', "(iayi)");
         if (r < 0)
                 goto fail;
 
-        while ((r = sd_bus_message_enter_container(reply, 'r', "yayi")) > 0) {
-                unsigned char family;
+        while ((r = sd_bus_message_enter_container(reply, 'r', "iayi")) > 0) {
+                int family, ifindex;
                 const void *a;
-                int ifindex;
                 size_t sz;
 
-                r = sd_bus_message_read(reply, "y", &family);
+                r = sd_bus_message_read(reply, "i", &family);
                 if (r < 0)
                         goto fail;
 
@@ -463,7 +525,7 @@ enum nss_status _nss_resolve_gethostbyaddr2_r(
                 return NSS_STATUS_UNAVAIL;
         }
 
-        if (len != PROTO_ADDRESS_SIZE(af)) {
+        if (len != FAMILY_ADDRESS_SIZE(af)) {
                 *errnop = EINVAL;
                 *h_errnop = NO_RECOVERY;
                 return NSS_STATUS_UNAVAIL;
@@ -487,7 +549,7 @@ enum nss_status _nss_resolve_gethostbyaddr2_r(
         if (r < 0)
                 goto fail;
 
-        r = sd_bus_message_append(req, "y", af);
+        r = sd_bus_message_append(req, "i", af);
         if (r < 0)
                 goto fail;
 
@@ -507,6 +569,29 @@ enum nss_status _nss_resolve_gethostbyaddr2_r(
                         return NSS_STATUS_NOTFOUND;
                 }
 
+                if (bus_error_shall_fallback(&error)) {
+
+                        enum nss_status (*fallback)(
+                                        const void* addr, socklen_t len,
+                                        int af,
+                                        struct hostent *result,
+                                        char *buffer, size_t buflen,
+                                        int *errnop, int *h_errnop,
+                                        int32_t *ttlp);
+
+                        fallback = (enum nss_status (*)(
+                                        const void* addr, socklen_t len,
+                                        int af,
+                                        struct hostent *result,
+                                        char *buffer, size_t buflen,
+                                        int *errnop, int *h_errnop,
+                                        int32_t *ttlp))
+                                find_fallback("libnss_dns.so.2", "_nss_dns_gethostbyaddr2_r");
+
+                        if (fallback)
+                                return fallback(addr, len, af, result, buffer, buflen, errnop, h_errnop, ttlp);
+                }
+
                 *errnop = -r;
                 *h_errnop = NO_RECOVERY;
                 return NSS_STATUS_UNAVAIL;