dhcpcd-discuss

On 29/10/2020 21:59, Dudemanguy wrote:
> On 10/29/20 4:47 PM, Roy Marples wrote:
> > It seems that you don't have a system logger running?
> > dhcpcd cannot connect to /dev/log from the looks of it.
> > Can you verify?
> >
> > Roy
>
> Right, I didn't have a system logger setup at the time. So I went ahead
> and installed the syslog-ng service, activated it, and then ran the new
> dhcpcd. It works now!

This patch should fix dhcpcd in privsep with seccomp and no syslogd running.
Let me know if it works for you!

Roy

diff --git a/src/dhcpcd.c b/src/dhcpcd.c
index 9b0a79a4..bd4cb74f 100644
--- a/src/dhcpcd.c
+++ b/src/dhcpcd.c
@@ -1860,7 +1860,7 @@ main(int argc, char **argv, char **envp)
 	ctx.dhcp6_wfd = -1;
 #endif
 #ifdef PRIVSEP
-	ctx.ps_root_fd = ctx.ps_data_fd = -1;
+	ctx.ps_root_fd = ctx.ps_syslog_fd = ctx.ps_data_fd = -1;
 	ctx.ps_inet_fd = ctx.ps_control_fd = -1;
 	TAILQ_INIT(&ctx.ps_processes);
 #endif
diff --git a/src/dhcpcd.h b/src/dhcpcd.h
index 8cdd3c19..b3cdf941 100644
--- a/src/dhcpcd.h
+++ b/src/dhcpcd.h
@@ -199,6 +199,7 @@ struct dhcpcd_ctx {
 	struct passwd *ps_user;	/* struct passwd for privsep user */
 	pid_t ps_root_pid;
 	int ps_root_fd;		/* Privileged Actioneer commands */
+	int ps_syslog_fd;	/* syslog(3) wrapper */
 	int ps_data_fd;		/* Data from root spawned processes */
 	struct eloop *ps_eloop;	/* eloop for polling root data */
 	struct ps_process_head ps_processes;	/* List of spawned processes */
diff --git a/src/logerr.c b/src/logerr.c
index ad337ba0..6d793082 100644
--- a/src/logerr.c
+++ b/src/logerr.c
@@ -47,11 +47,15 @@
 #undef LOGERR_TAG
 #endif
 
+/* syslog protocol is 1k message max, RFC 3164 section 4.1 */
+#define LOGERR_SYSLOGBUF	1024 + sizeof(int)
+
 #define UNUSED(a)		(void)(a)
 
 struct logctx {
 	char		 log_buf[BUFSIZ];
 	unsigned int	 log_opts;
+	int		 log_syslogfd;
 #ifndef SMALL
 	FILE		*log_file;
 #ifdef LOGERR_TAG
@@ -63,9 +67,10 @@ struct logctx {
 static struct logctx _logctx = {
 	/* syslog style, but without the hostname or tag. */
 	.log_opts = LOGERR_LOG | LOGERR_LOG_DATE | LOGERR_LOG_PID,
+	.log_syslogfd = -1,
 };
 
-#if defined(LOGERR_TAG) && defined(__linux__)
+#if defined(__linux__)
 /* Poor man's getprogname(3). */
 static char *_logprog;
 static const char *
@@ -79,9 +84,12 @@ getprogname(void)
 		 * so zero the buffer. */
 		if ((_logprog = calloc(1, PATH_MAX + 1)) == NULL)
 			return NULL;
+		if (readlink("/proc/self/exe", _logprog, PATH_MAX + 1) == -1) {
+			free(_logprog);
+			_logprog = NULL;
+			return NULL;
+		}
 	}
-	if (readlink("/proc/self/exe", _logprog, PATH_MAX + 1) == -1)
-		return NULL;
 	if (_logprog[0] == '[')
 		return NULL;
 	p = strrchr(_logprog, '/');
@@ -198,22 +206,33 @@ vlogmessage(int pri, const char *fmt, va_list args)
 	struct logctx *ctx = &_logctx;
 	int len = 0;
 
+	if (ctx->log_syslogfd != -1) {
+		char buf[LOGERR_SYSLOGBUF];
+
+		memcpy(buf, &pri, sizeof(pri));
+		len = vsnprintf(buf + sizeof(pri), sizeof(buf) - sizeof(pri),
+		    fmt, args);
+		if (len != -1)
+			len = (int)write(ctx->log_syslogfd, buf,
+			    ((size_t)++len) + sizeof(pri));
+		return len;
+	}
+
 	if (ctx->log_opts & LOGERR_ERR &&
 	    (pri <= LOG_ERR ||
 	    (!(ctx->log_opts & LOGERR_QUIET) && pri <= LOG_INFO) ||
 	    (ctx->log_opts & LOGERR_DEBUG && pri <= LOG_DEBUG)))
 		len = vlogprintf_r(ctx, stderr, fmt, args);
 
-	if (!(ctx->log_opts & LOGERR_LOG))
-		return len;
-
 #ifndef SMALL
 	if (ctx->log_file != NULL &&
 	    (pri != LOG_DEBUG || (ctx->log_opts & LOGERR_DEBUG)))
 		len = vlogprintf_r(ctx, ctx->log_file, fmt, args);
 #endif
 
-	vsyslog(pri, fmt, args);
+	if (ctx->log_opts & LOGERR_LOG)
+		vsyslog(pri, fmt, args);
+
 	return len;
 }
 #if defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ > 5))
@@ -331,6 +350,43 @@ log_errx(const char *fmt, ...)
 	va_end(args);
 }
 
+int
+loggetsyslogfd(void)
+{
+	struct logctx *ctx = &_logctx;
+
+	return ctx->log_syslogfd;
+}
+
+void
+logsetsyslogfd(int fd)
+{
+	struct logctx *ctx = &_logctx;
+
+	ctx->log_syslogfd = fd;
+}
+
+int
+loghandlesyslogfd(int fd)
+{
+	char buf[LOGERR_SYSLOGBUF];
+	int len, pri;
+
+	len = (int)read(fd, buf, sizeof(buf));
+	if (len == -1)
+		return -1;
+
+	/* Ensure we have pri and a terminator */
+	if (len < (int)sizeof(pri) + 1 || buf[len - 1] != '\0') {
+		errno = EINVAL;
+		return -1;
+	}
+
+	memcpy(&pri, buf, sizeof(pri));
+	logmessage(pri, "%s", buf + sizeof(pri));
+	return len;
+}
+
 unsigned int
 loggetopts(void)
 {
@@ -373,15 +429,9 @@ logopen(const char *path)
 
 	(void)setvbuf(stderr, ctx->log_buf, _IOLBF, sizeof(ctx->log_buf));
 
-	if (!(ctx->log_opts & LOGERR_LOG))
-		return 1;
-
-#ifdef LOG_NDELAY
-	opts |= LOG_NDELAY;
-#endif
 	if (ctx->log_opts & LOGERR_LOG_PID)
 		opts |= LOG_PID;
-	openlog(NULL, opts, LOGERR_SYSLOG_FACILITY);
+	openlog(getprogname(), opts, LOGERR_SYSLOG_FACILITY);
 	if (path == NULL)
 		return 1;
 
@@ -410,7 +460,7 @@ logclose(void)
 	fclose(ctx->log_file);
 	ctx->log_file = NULL;
 #endif
-#if defined(LOGERR_TAG) && defined(__linux__)
+#if defined(__linux__)
 	free(_logprog);
 #endif
 }
diff --git a/src/logerr.h b/src/logerr.h
index 4b4d6dc4..c1b80153 100644
--- a/src/logerr.h
+++ b/src/logerr.h
@@ -76,6 +76,11 @@ __printflike(2, 3) void logerrmessage(int pri, const char *fmt, ...);
 #define logerr(...)	log_err(__VA_ARGS__)
 #define logerrx(...)	log_errx(__VA_ARGS__)
 
+/* For syslog in a chroot */
+int loggetsyslogfd(void);
+void logsetsyslogfd(int);
+int loghandlesyslogfd(int);
+
 unsigned int loggetopts(void);
 void logsetopts(unsigned int);
 #define	LOGERR_DEBUG	(1U << 6)
diff --git a/src/privsep-root.c b/src/privsep-root.c
index 770dd953..209f2624 100644
--- a/src/privsep-root.c
+++ b/src/privsep-root.c
@@ -780,18 +780,34 @@ ps_root_dispatch(void *arg)
 		logerr(__func__);
 }
 
+static void
+ps_root_syslog(void *arg)
+{
+	struct dhcpcd_ctx *ctx = arg;
+
+	if (loghandlesyslogfd(ctx->ps_syslog_fd) == -1)
+		logerr(__func__);
+}
+
 pid_t
 ps_root_start(struct dhcpcd_ctx *ctx)
 {
-	int fd[2];
+	int logfd[2], datafd[2];
 	pid_t pid;
 
-	if (socketpair(AF_UNIX, SOCK_DGRAM | SOCK_CXNB, 0, fd) == -1)
+	if (xsocketpair(AF_UNIX, SOCK_DGRAM | SOCK_CXNB, 0, logfd) == -1)
 		return -1;
-	if (ps_setbuf_fdpair(fd) == -1)
+#ifdef PRIVSEP_RIGHTS
+	if (ps_rights_limit_fdpair(logfd) == -1)
+		return -1;
+#endif
+
+	if (socketpair(AF_UNIX, SOCK_DGRAM | SOCK_CXNB, 0, datafd) == -1)
+		return -1;
+	if (ps_setbuf_fdpair(datafd) == -1)
 		return -1;
 #ifdef PRIVSEP_RIGHTS
-	if (ps_rights_limit_fdpair(fd) == -1)
+	if (ps_rights_limit_fdpair(datafd) == -1)
 		return -1;
 #endif
 
@@ -800,14 +816,22 @@ ps_root_start(struct dhcpcd_ctx *ctx)
 	    ps_root_startcb, ps_root_signalcb, 0);
 
 	if (pid == 0) {
-		ctx->ps_data_fd = fd[1];
-		close(fd[0]);
+		ctx->ps_syslog_fd = logfd[1];
+		if (eloop_event_add(ctx->eloop, ctx->ps_syslog_fd,
+		    ps_root_syslog, ctx) == -1)
+			return -1;
+		close(logfd[0]);
+		ctx->ps_data_fd = datafd[1];
+		close(datafd[0]);
 		return 0;
 	} else if (pid == -1)
 		return -1;
 
-	ctx->ps_data_fd = fd[0];
-	close(fd[1]);
+	logsetsyslogfd(logfd[0]);
+	close(logfd[1]);
+
+	ctx->ps_data_fd = datafd[0];
+	close(datafd[1]);
 	if (eloop_event_add(ctx->eloop, ctx->ps_data_fd,
 	    ps_root_dispatch, ctx) == -1)
 		return -1;
diff --git a/src/privsep.c b/src/privsep.c
index e9fa463f..6e76902a 100644
--- a/src/privsep.c
+++ b/src/privsep.c
@@ -542,6 +542,19 @@ ps_mastersandbox(struct dhcpcd_ctx *ctx, const char *_pledge)
 	dropped = ps_dropprivs(ctx);
 	if (forked)
 		ctx->options |= DHCPCD_FORKED;
+
+	/*
+	 * If we don't have a root process, we cannot use syslog.
+	 * If it cannot be opened before chrooting then syslog(3) will fail.
+	 * openlog(3) does not return an error which doubly sucks.
+	 */
+	if (ctx->ps_root_fd == -1) {
+		unsigned int logopts = loggetopts();
+
+		logopts &= ~LOGERR_LOG;
+		logsetopts(logopts);
+	}
+
 	if (dropped == -1) {
 		logerr("%s: ps_dropprivs", __func__);
 		return -1;