1#include <unistd.h>
 2#include <signal.h>
 3#include "syscall.h"
 4#include "libc.h"
 5
 6struct ctx {
 7	int id, eid, sid;
 8	int nr, ret;
 9};
10
11static void do_setxid(void *p)
12{
13	struct ctx *c = p;
14	if (c->ret<0) return;
15	int ret = __syscall(c->nr, c->id, c->eid, c->sid);
16	if (ret && !c->ret) {
17		/* If one thread fails to set ids after another has already
18		 * succeeded, forcibly killing the process is the only safe
19		 * thing to do. State is inconsistent and dangerous. Use
20		 * SIGKILL because it is uncatchable. */
21		__block_all_sigs(0);
22		__syscall(SYS_kill, __syscall(SYS_getpid), SIGKILL);
23	}
24	c->ret = ret;
25}
26
27int __setxid(int nr, int id, int eid, int sid)
28{
29	/* ret is initially nonzero so that failure of the first thread does not
30	 * trigger the safety kill above. */
31	struct ctx c = { .nr = nr, .id = id, .eid = eid, .sid = sid, .ret = 1 };
32	__synccall(do_setxid, &c);
33	return __syscall_ret(c.ret > 0 ? -EAGAIN : c.ret);
34}