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, 22 insertions, 2 deletions

diff --git a/libc/sysdeps/linux/common/setegid.c b/libc/sysdeps/linux/common/setegid.c
index 90928c247..100a34568 100644
--- a/libc/sysdeps/linux/common/setegid.c
+++ b/libc/sysdeps/linux/common/setegid.c
@@ -1,8 +1,28 @@
-#include <stdlib.h>
+#define _GNU_SOURCE
 #include <unistd.h>
+#include <stdio.h>
+#include <errno.h>
+#include <grp.h>
 #include <sys/types.h>
+#include <sys/syscall.h>
 
 int setegid(gid_t gid)
 {
-	return setregid(-1, gid);
+    int result;
+
+    if (gid == (gid_t) ~0)
+    {
+	__set_errno (EINVAL);
+	return -1;
+    }
+
+#ifdef __NR_setresgid
+    result = setresgid(-1, gid, -1);
+    if (result == -1 && errno == ENOSYS)
+	/* Will also set the saved group ID if egid != gid,
+	 * making it impossible to switch back...*/
+#endif
+	result = setregid(-1, gid);
+
+    return result;
 }