virtiofsd: add --syslog command-line option

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>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

tools/virtiofsd/fuse_lowlevel.h

@@ -1795,6 +1795,7 @@ struct fuse_cmdline_opts {
     int show_version;
     int show_help;
     int print_capabilities;
+    int syslog;
     unsigned int max_idle_threads;
 };
 

tools/virtiofsd/helper.c

@@ -54,6 +54,7 @@ static const struct fuse_opt fuse_helper_opts[] = {
     FUSE_HELPER_OPT("subtype=", nodefault_subtype),
     FUSE_OPT_KEY("subtype=", FUSE_OPT_KEY_KEEP),
     FUSE_HELPER_OPT("max_idle_threads=%u", max_idle_threads),
+    FUSE_HELPER_OPT("--syslog", syslog),
     FUSE_OPT_END
 };
 
@@ -138,6 +139,7 @@ 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"
            "    -o max_idle_threads        the maximum number of idle worker "

tools/virtiofsd/passthrough_ll.c

@@ -58,6 +58,7 @@
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <sys/xattr.h>
+#include <syslog.h>
 #include <unistd.h>
 
 #include "passthrough_helpers.h"
@@ -138,6 +139,7 @@ static const struct fuse_opt lo_opts[] = {
     { "norace", 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);
 
@@ -2262,11 +2264,12 @@ static void setup_mounts(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, struct fuse_session *se)
+static void setup_sandbox(struct lo_data *lo, struct fuse_session *se,
+                          bool enable_syslog)
 {
     setup_namespaces(lo, se);
     setup_mounts(lo->source);
-    setup_seccomp();
+    setup_seccomp(enable_syslog);
 }
 
 /* Raise the maximum number of open file descriptors */
@@ -2298,6 +2301,42 @@ static void setup_nofile_rlimit(void)
     }
 }
 
+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);
@@ -2336,6 +2375,11 @@ 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();
@@ -2424,7 +2468,7 @@ int main(int argc, char *argv[])
     /* Must be before sandbox since it wants /proc */
     setup_capng();
 
-    setup_sandbox(&lo, se);
+    setup_sandbox(&lo, se, opts.syslog);
 
     /* Block until ctrl+c or fusermount -u */
     ret = virtio_loop(se);

tools/virtiofsd/seccomp.c

@@ -107,11 +107,28 @@ 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 */
@@ -126,13 +143,10 @@ 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 */

tools/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 */