Feature: uid support in run_as

src/utils.c

@@ -28,6 +28,7 @@
 #include <unistd.h>
 #include <string.h>
 #include <errno.h>
+#include <ctype.h>
 #ifndef __MINGW32__
 #include <pwd.h>
 #endif
@@ -86,6 +87,15 @@ ss_itoa(int i)
     return p;
 }
 
+int
+ss_isnumeric(const char *s) {
+    if (!s || !*s)
+        return 0;
+    while (isdigit(*s))
+        ++s;
+    return *s == '\0';
+}
+
 /*
  * setuid() and setgid() for a specified user.
  */
@@ -94,6 +104,18 @@ run_as(const char *user)
 {
 #ifndef __MINGW32__
     if (user[0]) {
+        printf("user: %s\n", user);
+        /* Convert user to a long integer if it is a non-negative number.
+         * -1 means it is a user name. */
+        long uid = -1;
+        if (ss_isnumeric(user)) {
+            errno = 0;
+            char *endptr;
+            uid = strtol(user, &endptr, 10);
+            if (errno || endptr == user)
+                uid = -1;
+        }
+
 #ifdef HAVE_GETPWNAM_R
         struct passwd pwdbuf, *pwd;
         size_t buflen;
@@ -105,7 +127,8 @@ run_as(const char *user)
             /* Note that we use getpwnam_r() instead of getpwnam(),
              * which returns its result in a statically allocated buffer and
              * cannot be considered thread safe. */
-            err = getpwnam_r(user, &pwdbuf, buf, buflen, &pwd);
+            err = uid >= 0 ? getpwuid_r((uid_t)uid, &pwdbuf, buf, buflen, &pwd)
+                : getpwnam_r(user, &pwdbuf, buf, buflen, &pwd);
 
             if (err == 0 && pwd) {
                 /* setgid first, because we may not be allowed to do it anymore after setuid */
@@ -145,7 +168,7 @@ run_as(const char *user)
         /* No getpwnam_r() :-(  We'll use getpwnam() and hope for the best. */
         struct passwd *pwd;
 
-        if (!(pwd = getpwnam(user))) {
+        if (!(pwd = uid >=0 ? getpwuid((uid_t)uid) : getpwnam(user))) {
             LOGE("run_as user %s could not be found.", user);
             return 0;
         }

src/utils.h

@@ -209,6 +209,7 @@ void ERROR(const char *s);
 #endif
 
 char *ss_itoa(int i);
+int ss_isnumeric(const char *s);
 int run_as(const char *user);
 void FATAL(const char *msg);
 void usage(void);