[PATCH 24/25] virtiofsd: add --syslog command-line option

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: Stefan Hajnoczi <stefanha@redhat.com>

Sometimes collecting output from stderr is inconvenient or does not fit
within the overall logging architecture.  Add syslog(3) support for
cases where stderr cannot be used.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
dgilbert: Reworked as a logging function
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 contrib/virtiofsd/fuse_lowlevel.h  |  1 +
 contrib/virtiofsd/helper.c         |  2 ++
 contrib/virtiofsd/passthrough_ll.c | 34 +++++++++++++++++++++++++++---
 contrib/virtiofsd/seccomp.c        | 32 ++++++++++++++++++++--------
 contrib/virtiofsd/seccomp.h        |  4 +++-
 5 files changed, 60 insertions(+), 13 deletions(-)

diff --git a/contrib/virtiofsd/fuse_lowlevel.h b/contrib/virtiofsd/fuse_lowlevel.h
index 13fd9791d5..112596caaf 100644
--- a/contrib/virtiofsd/fuse_lowlevel.h
+++ b/contrib/virtiofsd/fuse_lowlevel.h
@@ -1798,6 +1798,7 @@ struct fuse_cmdline_opts {
 	int show_help;
 	int print_capabilities;
 	int clone_fd;
+	int syslog;
 	unsigned int max_idle_threads;
 };
 
diff --git a/contrib/virtiofsd/helper.c b/contrib/virtiofsd/helper.c
index 08e00c0d13..b1e45aee05 100644
--- a/contrib/virtiofsd/helper.c
+++ b/contrib/virtiofsd/helper.c
@@ -53,6 +53,7 @@ static const struct fuse_opt fuse_helper_opts[] = {
 #endif
 	FUSE_HELPER_OPT("clone_fd",	clone_fd),
 	FUSE_HELPER_OPT("max_idle_threads=%u", max_idle_threads),
+	FUSE_HELPER_OPT("--syslog",	syslog),
 	FUSE_OPT_END
 };
 
@@ -135,6 +136,7 @@ void fuse_cmdline_help(void)
 	       "    -V   --version             print version\n"
 	       "    --print-capabilities       print vhost-user.json\n"
 	       "    -d   -o debug              enable debug output (implies -f)\n"
+	       "    --syslog                   log to syslog (default stderr)\n"
 	       "    -f                         foreground operation\n"
 	       "    --daemonize                run in background\n"
 	       "    -s                         disable multi-threaded operation\n"
diff --git a/contrib/virtiofsd/passthrough_ll.c b/contrib/virtiofsd/passthrough_ll.c
index 25f7ad854a..b413687720 100644
--- a/contrib/virtiofsd/passthrough_ll.c
+++ b/contrib/virtiofsd/passthrough_ll.c
@@ -42,6 +42,7 @@
 #include <stddef.h>
 #include <stdbool.h>
 #include <string.h>
+#include <syslog.h>
 #include <limits.h>
 #include <dirent.h>
 #include <assert.h>
@@ -151,6 +152,7 @@ static const struct fuse_opt lo_opts[] = {
 	  offsetof(struct lo_data, norace), 1 },
 	FUSE_OPT_END
 };
+static bool use_syslog = false;
 
 static void unref_inode(struct lo_data *lo, struct lo_inode *inode, uint64_t n);
 
@@ -2103,13 +2105,13 @@ static void setup_mount_namespace(const char *source)
  * Lock down this process to prevent access to other processes or files outside
  * source directory.  This reduces the impact of arbitrary code execution bugs.
  */
-static void setup_sandbox(struct lo_data *lo)
+static void setup_sandbox(struct lo_data *lo, bool enable_syslog)
 {
 	setup_pid_namespace();
 	setup_proc_self_fd(lo);
 	setup_net_namespace();
 	setup_mount_namespace(lo->source);
-	setup_seccomp();
+	setup_seccomp(enable_syslog);
 }
 
 /* Raise the maximum number of open file descriptors to the system limit */
@@ -2142,6 +2144,27 @@ static void setup_nofile_rlimit(void)
 	g_free(nr_open);
 }
 
+static void log_func(enum fuse_log_level level,
+		     const char *fmt, va_list ap)
+{
+	if (use_syslog) {
+		int priority = LOG_ERR;
+		switch (level) {
+			case FUSE_LOG_EMERG:   priority = LOG_EMERG;   break;
+			case FUSE_LOG_ALERT:   priority = LOG_ALERT;   break;
+			case FUSE_LOG_CRIT:    priority = LOG_CRIT;    break;
+			case FUSE_LOG_ERR:     priority = LOG_ERR;     break;
+			case FUSE_LOG_WARNING: priority = LOG_WARNING; break;
+			case FUSE_LOG_NOTICE:  priority = LOG_NOTICE;  break;
+			case FUSE_LOG_INFO:    priority = LOG_INFO;    break;
+			case FUSE_LOG_DEBUG:   priority = LOG_DEBUG;   break;
+		}
+		vsyslog(priority, fmt, ap);
+	} else {
+		vfprintf(stderr, fmt, ap);
+	}
+}
+
 int main(int argc, char *argv[])
 {
 	struct fuse_args args = FUSE_ARGS_INIT(argc, argv);
@@ -2179,6 +2202,11 @@ int main(int argc, char *argv[])
 
 	if (fuse_parse_cmdline(&args, &opts) != 0)
 		return 1;
+	fuse_set_log_func(log_func);
+	use_syslog = opts.syslog;
+	if (use_syslog) {
+	    openlog("virtiofsd", LOG_PID, LOG_DAEMON);
+	}
 	if (opts.show_help) {
 		printf("usage: %s [options]\n\n", argv[0]);
 		fuse_cmdline_help();
@@ -2260,7 +2288,7 @@ int main(int argc, char *argv[])
 
 	fuse_daemonize(opts.foreground);
 
-	setup_sandbox(&lo);
+	setup_sandbox(&lo, opts.syslog);
 
 	/* Block until ctrl+c or fusermount -u */
 	ret = virtio_loop(se);
diff --git a/contrib/virtiofsd/seccomp.c b/contrib/virtiofsd/seccomp.c
index df1390d6be..77bc405bdc 100644
--- a/contrib/virtiofsd/seccomp.c
+++ b/contrib/virtiofsd/seccomp.c
@@ -88,11 +88,28 @@ static const int syscall_whitelist[] = {
     SCMP_SYS(writev),
 };
 
-void setup_seccomp(void)
+/* Syscalls used when --syslog is enabled */
+static const int syscall_whitelist_syslog[] = {
+    SCMP_SYS(sendto),
+};
+
+static void add_whitelist(scmp_filter_ctx ctx, const int syscalls[], size_t len)
 {
-    scmp_filter_ctx ctx;
     size_t i;
 
+    for (i = 0; i < len; i++) {
+        if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW, syscalls[i], 0) != 0) {
+            fuse_log(FUSE_LOG_ERR, "seccomp_rule_add syscall %d failed\n",
+                     syscalls[i]);
+            exit(1);
+        }
+    }
+}
+
+void setup_seccomp(bool enable_syslog)
+{
+    scmp_filter_ctx ctx;
+
 #ifdef SCMP_ACT_KILL_PROCESS
     ctx = seccomp_init(SCMP_ACT_KILL_PROCESS);
     /* Handle a newer libseccomp but an older kernel */
@@ -107,13 +124,10 @@ void setup_seccomp(void)
         exit(1);
     }
 
-    for (i = 0; i < G_N_ELEMENTS(syscall_whitelist); i++) {
-        if (seccomp_rule_add(ctx, SCMP_ACT_ALLOW,
-                             syscall_whitelist[i], 0) != 0) {
-            fuse_log(FUSE_LOG_ERR, "seccomp_rule_add syscall %d",
-                     syscall_whitelist[i]);
-            exit(1);
-        }
+    add_whitelist(ctx, syscall_whitelist, G_N_ELEMENTS(syscall_whitelist));
+    if (enable_syslog) {
+        add_whitelist(ctx, syscall_whitelist_syslog,
+                      G_N_ELEMENTS(syscall_whitelist_syslog));
     }
 
     /* libvhost-user calls this for post-copy migration, we don't need it */
diff --git a/contrib/virtiofsd/seccomp.h b/contrib/virtiofsd/seccomp.h
index 86bce72652..d47c8eade6 100644
--- a/contrib/virtiofsd/seccomp.h
+++ b/contrib/virtiofsd/seccomp.h
@@ -9,6 +9,8 @@
 #ifndef VIRTIOFSD_SECCOMP_H
 #define VIRTIOFSD_SECCOMP_H
 
-void setup_seccomp(void);
+#include <stdbool.h>
+
+void setup_seccomp(bool enable_syslog);
 
 #endif /* VIRTIOFSD_SECCOMP_H */
-- 
2.23.0