1 files changed, 34 insertions, 0 deletions
diff --git a/libc-top-half/musl/src/unistd/setxid.c b/libc-top-half/musl/src/unistd/setxid.c
new file mode 100644
index 0000000..487c1a1
--- /dev/null
+++ b/libc-top-half/musl/src/unistd/setxid.c
@@ -0,0 +1,34 @@
+#include <unistd.h>
+#include <signal.h>
+#include "syscall.h"
+#include "libc.h"
+
+struct ctx {
+	int id, eid, sid;
+	int nr, ret;
+};
+
+static void do_setxid(void *p)
+{
+	struct ctx *c = p;
+	if (c->ret<0) return;
+	int ret = __syscall(c->nr, c->id, c->eid, c->sid);
+	if (ret && !c->ret) {
+		/* If one thread fails to set ids after another has already
+		 * succeeded, forcibly killing the process is the only safe
+		 * thing to do. State is inconsistent and dangerous. Use
+		 * SIGKILL because it is uncatchable. */
+		__block_all_sigs(0);
+		__syscall(SYS_kill, __syscall(SYS_getpid), SIGKILL);
+	}
+	c->ret = ret;
+}
+
+int __setxid(int nr, int id, int eid, int sid)
+{
+	/* ret is initially nonzero so that failure of the first thread does not
+	 * trigger the safety kill above. */
+	struct ctx c = { .nr = nr, .id = id, .eid = eid, .sid = sid, .ret = 1 };
+	__synccall(do_setxid, &c);
+	return __syscall_ret(c.ret);
+}