From dc8d50bd8d382505ca7a34d501097ce7c181803b Mon Sep 17 00:00:00 2001
From: lns <matzeton@googlemail.com>
Date: Thu, 26 Apr 2018 15:31:31 +0200
Subject: POTD skeleton #30.

Signed-off-by: lns <matzeton@googlemail.com>
---
 src/utils.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

(limited to 'src/utils.c')

diff --git a/src/utils.c b/src/utils.c
index 996a8a7..ada3c13 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -5,6 +5,8 @@
 #include <stdarg.h>
 #include <fcntl.h>
 #include <signal.h>
+#include <pwd.h>
+#include <grp.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/wait.h>
@@ -153,6 +155,8 @@ int redirect_devnull_to(int fds, ...)
 
     if (null_fd < 0)
         null_fd = open("/dev/null", O_RDWR);
+    if (null_fd < 0)
+        return -1;
     assert(null_fd >= 0);
 
     va_start(ap, fds);
@@ -169,5 +173,27 @@ int redirect_devnull_to(int fds, ...)
 
 int change_user_group(const char *user, const char *group)
 {
+    struct passwd *pwd = NULL;
+    struct group *grp = NULL;
+    gid_t gid;
+
+    pwd = getpwnam(user);
+    if (!pwd)
+        return 1;
+
+    if (!group) {
+        gid = pwd->pw_gid;
+    } else {
+        grp = getgrnam(group);
+        if (!grp)
+            return 1;
+        gid = grp->gr_gid;
+    }
+
+    if (setregid(gid, gid))
+        return 1;
+    if (setreuid(pwd->pw_uid, pwd->pw_uid))
+        return 1;
+
     return 0;
 }
-- 
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