141 lines
5.1 KiB
Diff
141 lines
5.1 KiB
Diff
From 7ab91cb307eb0a518f4a956674a108221538fc88 Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Mon, 22 Nov 2021 15:17:34 +0100
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Subject: [PATCH] resolved: properly signal transient errors back to NSS stack
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NSS mostly knows four error cases: SUCCESS, NOTFOUND, UNAVAIL, TRYAGAIN,
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and they can all be used in nsswitch.conf to route requests.
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So far nss-resolve would return SUCCESS + NOTFOUND + UNAVAIL. Let's also
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return TRYAGAIN in some cases, specifically the ones where we are
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currntly unable to resolve a request but likely could later. i.e.
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errors caused by networking issues or such.
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Fixes: #20786
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(cherry picked from commit ae78529fc75027b3487b64e0d22a572fd9c8ffeb)
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Conflict:NA
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Reference:https://github.com/systemd/systemd/commit/7ab91cb307eb0a518f4a956674a108221538fc88
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---
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src/nss-resolve/nss-resolve.c | 55 +++++++++++++++++++++++++++++------
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1 file changed, 46 insertions(+), 9 deletions(-)
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diff --git a/src/nss-resolve/nss-resolve.c b/src/nss-resolve/nss-resolve.c
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index e2a29475a2..4f54973202 100644
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--- a/src/nss-resolve/nss-resolve.c
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+++ b/src/nss-resolve/nss-resolve.c
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@@ -41,6 +41,9 @@ NSS_GETHOSTBYNAME_PROTOTYPES(resolve);
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NSS_GETHOSTBYADDR_PROTOTYPES(resolve);
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static bool error_shall_fallback(const char *error_id) {
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+ /* The Varlink errors where we shall signal "please fallback" back to the NSS stack, so that some
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+ * fallback module can be loaded. (These are mostly all Varlink-internal errors, as apparently we
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+ * then were unable to even do IPC with systemd-resolved.) */
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return STR_IN_SET(error_id,
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VARLINK_ERROR_DISCONNECTED,
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VARLINK_ERROR_TIMEOUT,
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@@ -50,6 +53,16 @@ static bool error_shall_fallback(const char *error_id) {
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VARLINK_ERROR_METHOD_NOT_IMPLEMENTED);
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}
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+static bool error_shall_try_again(const char *error_id) {
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+ /* The Varlink errors where we shall signal "can't answer now but might be able to later" back to the
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+ * NSS stack. These are all errors that indicate lack of configuration or network problems. */
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+ return STR_IN_SET(error_id,
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+ "io.systemd.Resolve.NoNameServers",
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+ "io.systemd.Resolve.QueryTimedOut",
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+ "io.systemd.Resolve.MaxAttemptsReached",
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+ "io.systemd.Resolve.NetworkDown");
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+}
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+
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static int connect_to_resolved(Varlink **ret) {
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_cleanup_(varlink_unrefp) Varlink *link = NULL;
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int r;
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@@ -242,9 +255,11 @@ enum nss_status _nss_resolve_gethostbyname4_r(
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if (r < 0)
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goto fail;
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if (!isempty(error_id)) {
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- if (!error_shall_fallback(error_id))
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- goto not_found;
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- goto fail;
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+ if (error_shall_try_again(error_id))
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+ goto try_again;
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+ if (error_shall_fallback(error_id))
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+ goto fail;
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+ goto not_found;
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}
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r = json_dispatch(rparams, resolve_hostname_reply_dispatch_table, NULL, json_dispatch_flags, &p);
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@@ -341,6 +356,12 @@ fail:
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not_found:
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*h_errnop = HOST_NOT_FOUND;
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return NSS_STATUS_NOTFOUND;
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+
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+try_again:
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+ UNPROTECT_ERRNO;
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+ *errnop = -r;
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+ *h_errnop = TRY_AGAIN;
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+ return NSS_STATUS_TRYAGAIN;
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}
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enum nss_status _nss_resolve_gethostbyname3_r(
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@@ -390,9 +411,11 @@ enum nss_status _nss_resolve_gethostbyname3_r(
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if (r < 0)
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goto fail;
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if (!isempty(error_id)) {
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- if (!error_shall_fallback(error_id))
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- goto not_found;
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- goto fail;
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+ if (error_shall_try_again(error_id))
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+ goto try_again;
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+ if (error_shall_fallback(error_id))
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+ goto fail;
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+ goto not_found;
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}
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r = json_dispatch(rparams, resolve_hostname_reply_dispatch_table, NULL, json_dispatch_flags, &p);
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@@ -508,6 +531,12 @@ fail:
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not_found:
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*h_errnop = HOST_NOT_FOUND;
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return NSS_STATUS_NOTFOUND;
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+
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+try_again:
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+ UNPROTECT_ERRNO;
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+ *errnop = -r;
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+ *h_errnop = TRY_AGAIN;
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+ return NSS_STATUS_TRYAGAIN;
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}
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typedef struct ResolveAddressReply {
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@@ -594,9 +623,11 @@ enum nss_status _nss_resolve_gethostbyaddr2_r(
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if (r < 0)
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goto fail;
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if (!isempty(error_id)) {
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- if (!error_shall_fallback(error_id))
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- goto not_found;
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- goto fail;
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+ if (error_shall_try_again(error_id))
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+ goto try_again;
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+ if (error_shall_fallback(error_id))
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+ goto fail;
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+ goto not_found;
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}
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r = json_dispatch(rparams, resolve_address_reply_dispatch_table, NULL, json_dispatch_flags, &p);
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@@ -694,6 +725,12 @@ fail:
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not_found:
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*h_errnop = HOST_NOT_FOUND;
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return NSS_STATUS_NOTFOUND;
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+
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+try_again:
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+ UNPROTECT_ERRNO;
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+ *errnop = -r;
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+ *h_errnop = TRY_AGAIN;
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+ return NSS_STATUS_TRYAGAIN;
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}
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NSS_GETHOSTBYNAME_FALLBACKS(resolve);
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--
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2.33.0
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