logger: do not rely only getlogin(3) telling who ran the command

The getlogin(3) is known not to always work, and when that happens it is
reasonable to try determine user of name by looking process owner and
passwd information.

Reference: http://man7.org/linux/man-pages/man3/getlogin.3.html
Signed-off-by: Sami Kerola <kerolasa@iki.fi>

diff --git a/misc-utils/logger.c b/misc-utils/logger.c
index 0c6dbbdd208f13e1340c6afc9c44cb1aa704e515..5204cef55f26990c8364a1487c4a12cb869bc7ad 100644 (file)
--- a/misc-utils/logger.c
+++ b/misc-utils/logger.c
@@ -50,6 +50,7 @@
 #include <arpa/inet.h>
 #include <netdb.h>
 #include <getopt.h>
+#include <pwd.h>
 
 #include "all-io.h"
 #include "c.h"
@@ -257,6 +258,16 @@ static int journald_entry(FILE *fp)
 }
 #endif
 
+static char *xgetlogin()
+{
+       char *cp;
+       struct passwd *pw;
+
+       if (!(cp = getlogin()) || !*cp)
+               cp = (pw = getpwuid(geteuid()))? pw->pw_name : "<someone>";
+       return cp;
+}
+
 static void mysyslog(int fd, int logflags, int pri, char *tag, char *msg)
 {
        char buf[1000], pid[30], *cp, *tp;
@@ -269,11 +280,8 @@ static void mysyslog(int fd, int logflags, int pri, char *tag, char *msg)
                        pid[0] = 0;
                if (tag)
                        cp = tag;
-               else {
-                       cp = getlogin();
-                       if (!cp)
-                               cp = "<someone>";
-               }
+               else
+                       cp = xgetlogin();
                time(&now);
                tp = ctime(&now) + 4;
 
@@ -438,7 +446,7 @@ int main(int argc, char **argv)
        else if (usock)
                LogSock = unix_socket(usock, socket_type);
        else
-               openlog(tag ? tag : getlogin(), logflags, 0);
+               openlog(tag ? tag : xgetlogin(), logflags, 0);
 
        /* log input line if appropriate */
        if (argc > 0) {