Merge pull request #11086 from poettering/nscd-cache-flush

flush nscd's caches when we register user/groups/hostnames

src/shared/meson.build

@@ -82,6 +82,8 @@ shared_sources = files('''
         install-printf.h
         install.c
         install.h
+        ip-protocol-list.c
+        ip-protocol-list.h
         journal-importer.c
         journal-importer.h
         journal-util.c
@@ -103,6 +105,8 @@ shared_sources = files('''
         module-util.h
         mount-util.c
         mount-util.h
+        nscd-flush.c
+        nscd-flush.h
         nsflags.c
         nsflags.h
         os-util.c
@@ -128,8 +132,6 @@ shared_sources = files('''
         serialize.h
         sleep-config.c
         sleep-config.h
-        ip-protocol-list.c
-        ip-protocol-list.h
         spawn-ask-password-agent.c
         spawn-ask-password-agent.h
         spawn-polkit-agent.c

src/shared/nscd-flush.c

@@ -0,0 +1,151 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+#include <sys/poll.h>
+
+#include "fd-util.h"
+#include "io-util.h"
+#include "nscd-flush.h"
+#include "socket-util.h"
+#include "strv.h"
+#include "time-util.h"
+
+#define NSCD_FLUSH_CACHE_TIMEOUT_USEC (5*USEC_PER_SEC)
+
+struct nscdInvalidateRequest {
+        int32_t version;
+        int32_t type; /* in glibc this is an enum. We don't replicate this here 1:1. Also, wtf, how unportable is that
+                       * even? */
+        int32_t key_len;
+        char dbname[];
+};
+
+static const union sockaddr_union nscd_sa = {
+        .un.sun_family = AF_UNIX,
+        .un.sun_path = "/run/nscd/socket",
+};
+
+static int nscd_flush_cache_one(const char *database, usec_t end) {
+        size_t req_size, has_written = 0, has_read = 0, l;
+        struct nscdInvalidateRequest *req;
+        _cleanup_close_ int fd = -1;
+        int32_t resp;
+        int events;
+
+        assert(database);
+
+        l = strlen(database);
+        req_size = offsetof(struct nscdInvalidateRequest, dbname) + l + 1;
+
+        req = alloca(req_size);
+        *req = (struct nscdInvalidateRequest) {
+                .version = 2,
+                .type = 10,
+                .key_len = l + 1,
+        };
+
+        strcpy(req->dbname, database);
+
+        fd = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
+        if (fd < 0)
+                return log_debug_errno(errno, "Failed to allocate nscd socket: %m");
+
+        /* Note: connect() returns EINPROGRESS if O_NONBLOCK is set and establishing a connection takes time. The
+         * kernel lets us know this way that the connection is now being established, and we should watch with poll()
+         * to learn when it is fully established. That said, AF_UNIX on Linux never triggers this IRL (connect() is
+         * always instant on AF_UNIX), hence handling this is mostly just an excercise in defensive, protocol-agnostic
+         * programming.
+         *
+         * connect() returns EAGAIN if the socket's backlog limit has been reached. When we see this we give up right
+         * away, after all this entire function here is written in a defensive style so that a non-responding nscd
+         * doesn't stall us for good. (Even if we wanted to handle this better: the Linux kernel doesn't really have a
+         * nice way to connect() to a server synchronously with a time limit that would also cover dealing with the
+         * backlog limit. After all SO_RCVTIMEO and SR_SNDTIMEO don't apply to connect(), and alarm() is frickin' ugly
+         * and not really reasonably usable from threads-aware code.) */
+        if (connect(fd, &nscd_sa.sa, SOCKADDR_UN_LEN(nscd_sa.un)) < 0) {
+                if (errno == EAGAIN)
+                        return log_debug_errno(errno, "nscd is overloaded (backlog limit reached) and refuses to take further connections: %m");
+                if (errno != EINPROGRESS)
+                        return log_debug_errno(errno, "Failed to connect to nscd socket: %m");
+
+                /* Continue in case of EINPROGRESS, but don't bother with send() or recv() until being notified that
+                 * establishing the connection is complete. */
+                events = 0;
+        } else
+                events = POLLIN|POLLOUT; /* Let's assume initially that we can write and read to the fd, to suppress
+                                          * one poll() invocation */
+        for (;;) {
+                usec_t p;
+
+                if (events & POLLOUT) {
+                        ssize_t m;
+
+                        assert(has_written < req_size);
+
+                        m = send(fd, (uint8_t*) req + has_written, req_size - has_written, MSG_NOSIGNAL);
+                        if (m < 0) {
+                                if (errno != EAGAIN) /* Note that EAGAIN is returned by the kernel whenever it can't
+                                                      * take the data right now, and that includes if the connect() is
+                                                      * asynchronous and we saw EINPROGRESS on it, and it hasn't
+                                                      * completed yet. */
+                                        return log_debug_errno(errno, "Failed to write to nscd socket: %m");
+                        } else
+                                has_written += m;
+                }
+
+                if (events & (POLLIN|POLLERR|POLLHUP)) {
+                        ssize_t m;
+
+                        if (has_read >= sizeof(resp))
+                                return log_debug_errno(SYNTHETIC_ERRNO(EIO), "Response from nscd longer than expected: %m");
+
+                        m = recv(fd, (uint8_t*) &resp + has_read, sizeof(resp) - has_read, 0);
+                        if (m < 0) {
+                                if (errno != EAGAIN)
+                                        return log_debug_errno(errno, "Failed to read from nscd socket: %m");
+                        } else if (m == 0) { /* EOF */
+                                if (has_read == 0 && has_written >= req_size) /* Older nscd immediately terminated the
+                                                                               * connection, accept that as OK */
+                                        return 1;
+
+                                return log_debug_errno(SYNTHETIC_ERRNO(EIO), "nscd prematurely ended connection.");
+                        } else
+                                has_read += m;
+                }
+
+                if (has_written >= req_size && has_read >= sizeof(resp)) { /* done? */
+                        if (resp < 0)
+                                return log_debug_errno(SYNTHETIC_ERRNO(EBADMSG), "nscd sent us a negative error numer: %i", resp);
+                        if (resp > 0)
+                                return log_debug_errno(resp, "nscd return failure code on invalidating '%s'.", database);
+                        return 1;
+                }
+
+                p = now(CLOCK_MONOTONIC);
+                if (p >= end)
+                        return -ETIMEDOUT;
+
+                events = fd_wait_for_event(fd, POLLIN | (has_written < req_size ? POLLOUT : 0), end - p);
+                if (events < 0)
+                        return events;
+        }
+}
+
+int nscd_flush_cache(char **databases) {
+        usec_t end;
+        int r = 0;
+        char **i;
+
+        /* Tries to invalidate the specified database in nscd. We do this carefully, with a 5s time-out, so that we
+         * don't block indefinitely on another service. */
+
+        end = usec_add(now(CLOCK_MONOTONIC), NSCD_FLUSH_CACHE_TIMEOUT_USEC);
+
+        STRV_FOREACH(i, databases) {
+                int k;
+
+                k = nscd_flush_cache_one(*i, end);
+                if (k < 0 && r >= 0)
+                        r = k;
+        }
+
+        return r;
+}

src/shared/nscd-flush.h

@@ -0,0 +1,4 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+#pragma once
+
+int nscd_flush_cache(char **databases);