setxid.c raw

   1  #include <unistd.h>
   2  #include <signal.h>
   3  #include "syscall.h"
   4  #include "libc.h"
   5  
   6  struct ctx {
   7  	int id, eid, sid;
   8  	int nr, ret;
   9  };
  10  
  11  static 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  
  27  int __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);
  34  }
  35