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authorLennart Poettering <lennart@poettering.net>2021-11-22 15:17:34 +0100
committerLennart Poettering <lennart@poettering.net>2021-11-22 22:33:40 +0100
commitae78529fc75027b3487b64e0d22a572fd9c8ffeb (patch)
tree6d28e30bee8904b5656cfc343bf7d0116cdd7015 /src/nss-resolve/nss-resolve.c
parentresolved: fix ResolveService() hostname handling (diff)
downloadsystemd-ae78529fc75027b3487b64e0d22a572fd9c8ffeb.tar.xz
systemd-ae78529fc75027b3487b64e0d22a572fd9c8ffeb.zip
resolved: properly signal transient errors back to NSS stack
NSS mostly knows four error cases: SUCCESS, NOTFOUND, UNAVAIL, TRYAGAIN, and they can all be used in nsswitch.conf to route requests. So far nss-resolve would return SUCCESS + NOTFOUND + UNAVAIL. Let's also return TRYAGAIN in some cases, specifically the ones where we are currntly unable to resolve a request but likely could later. i.e. errors caused by networking issues or such. Fixes: #20786
Diffstat (limited to 'src/nss-resolve/nss-resolve.c')
-rw-r--r--src/nss-resolve/nss-resolve.c55
1 files changed, 46 insertions, 9 deletions
diff --git a/src/nss-resolve/nss-resolve.c b/src/nss-resolve/nss-resolve.c
index d77ffdd9f2..951d141f35 100644
--- a/src/nss-resolve/nss-resolve.c
+++ b/src/nss-resolve/nss-resolve.c
@@ -41,6 +41,9 @@ NSS_GETHOSTBYNAME_PROTOTYPES(resolve);
NSS_GETHOSTBYADDR_PROTOTYPES(resolve);
static bool error_shall_fallback(const char *error_id) {
+ /* The Varlink errors where we shall signal "please fallback" back to the NSS stack, so that some
+ * fallback module can be loaded. (These are mostly all Varlink-internal errors, as apparently we
+ * then were unable to even do IPC with systemd-resolved.) */
return STR_IN_SET(error_id,
VARLINK_ERROR_DISCONNECTED,
VARLINK_ERROR_TIMEOUT,
@@ -50,6 +53,16 @@ static bool error_shall_fallback(const char *error_id) {
VARLINK_ERROR_METHOD_NOT_IMPLEMENTED);
}
+static bool error_shall_try_again(const char *error_id) {
+ /* The Varlink errors where we shall signal "can't answer now but might be able to later" back to the
+ * NSS stack. These are all errors that indicate lack of configuration or network problems. */
+ return STR_IN_SET(error_id,
+ "io.systemd.Resolve.NoNameServers",
+ "io.systemd.Resolve.QueryTimedOut",
+ "io.systemd.Resolve.MaxAttemptsReached",
+ "io.systemd.Resolve.NetworkDown");
+}
+
static int connect_to_resolved(Varlink **ret) {
_cleanup_(varlink_unrefp) Varlink *link = NULL;
int r;
@@ -242,9 +255,11 @@ enum nss_status _nss_resolve_gethostbyname4_r(
if (r < 0)
goto fail;
if (!isempty(error_id)) {
- if (!error_shall_fallback(error_id))
- goto not_found;
- goto fail;
+ if (error_shall_try_again(error_id))
+ goto try_again;
+ if (error_shall_fallback(error_id))
+ goto fail;
+ goto not_found;
}
r = json_dispatch(rparams, resolve_hostname_reply_dispatch_table, NULL, json_dispatch_flags, &p);
@@ -341,6 +356,12 @@ fail:
not_found:
*h_errnop = HOST_NOT_FOUND;
return NSS_STATUS_NOTFOUND;
+
+try_again:
+ UNPROTECT_ERRNO;
+ *errnop = -r;
+ *h_errnop = TRY_AGAIN;
+ return NSS_STATUS_TRYAGAIN;
}
enum nss_status _nss_resolve_gethostbyname3_r(
@@ -390,9 +411,11 @@ enum nss_status _nss_resolve_gethostbyname3_r(
if (r < 0)
goto fail;
if (!isempty(error_id)) {
- if (!error_shall_fallback(error_id))
- goto not_found;
- goto fail;
+ if (error_shall_try_again(error_id))
+ goto try_again;
+ if (error_shall_fallback(error_id))
+ goto fail;
+ goto not_found;
}
r = json_dispatch(rparams, resolve_hostname_reply_dispatch_table, NULL, json_dispatch_flags, &p);
@@ -508,6 +531,12 @@ fail:
not_found:
*h_errnop = HOST_NOT_FOUND;
return NSS_STATUS_NOTFOUND;
+
+try_again:
+ UNPROTECT_ERRNO;
+ *errnop = -r;
+ *h_errnop = TRY_AGAIN;
+ return NSS_STATUS_TRYAGAIN;
}
typedef struct ResolveAddressReply {
@@ -594,9 +623,11 @@ enum nss_status _nss_resolve_gethostbyaddr2_r(
if (r < 0)
goto fail;
if (!isempty(error_id)) {
- if (!error_shall_fallback(error_id))
- goto not_found;
- goto fail;
+ if (error_shall_try_again(error_id))
+ goto try_again;
+ if (error_shall_fallback(error_id))
+ goto fail;
+ goto not_found;
}
r = json_dispatch(rparams, resolve_address_reply_dispatch_table, NULL, json_dispatch_flags, &p);
@@ -694,6 +725,12 @@ fail:
not_found:
*h_errnop = HOST_NOT_FOUND;
return NSS_STATUS_NOTFOUND;
+
+try_again:
+ UNPROTECT_ERRNO;
+ *errnop = -r;
+ *h_errnop = TRY_AGAIN;
+ return NSS_STATUS_TRYAGAIN;
}
NSS_GETHOSTBYNAME_FALLBACKS(resolve);