Both setegid and seteuid were implemented suboptimally, such that

we were unable to switch back to the original saved group/user ID.
 -Erik

1 files changed, 20 insertions, 1 deletions

diff --git a/libc/sysdeps/linux/common/seteuid.c b/libc/sysdeps/linux/common/seteuid.c
index fbf60909d..e970e0711 100644
--- a/libc/sysdeps/linux/common/seteuid.c
+++ b/libc/sysdeps/linux/common/seteuid.c
@@ -1,9 +1,28 @@
+#define _GNU_SOURCE
 #include <unistd.h>
 #include <stdio.h>
 #include <errno.h>
+#include <pwd.h>
 #include <sys/types.h>
+#include <sys/syscall.h>
 
 int seteuid(uid_t uid)
 {
-    return setreuid(-1, uid);
+    int result;
+
+    if (uid == (uid_t) ~0)
+    {
+	__set_errno (EINVAL);
+	return -1;
+    }
+
+#ifdef __NR_setresuid
+    result = setresuid(-1, uid, -1);
+    if (result == -1 && errno == ENOSYS)
+	/* Will also set the saved user ID if euid != uid,
+	 * making it impossible to switch back...*/
+#endif
+	result = setreuid(-1, uid);
+
+    return result;
 }