src/unistd/setxid.c

   1 #include <unistd.h>
   2 #include <errno.h>
   3 #include "syscall.h"
   4 #include "libc.h"
   5 #include "pthread_impl.h"
   6
   7 struct ctx {
   8         int id, eid, sid;
   9         int nr, err;
  10 };
  11
  12 static void do_setxid(void *p)
  13 {
  14         struct ctx *c = p;
  15         if (c->err>0) return;
  16         int ret = -__syscall(c->nr, c->id, c->eid, c->sid);
  17         if (ret && !c->err) {
  18                 /* If one thread fails to set ids after another has already
  19                  * succeeded, forcibly killing the process is the only safe
  20                  * thing to do. State is inconsistent and dangerous. Use
  21                  * SIGKILL because it is uncatchable. */
  22                 __block_all_sigs(0);
  23                 __syscall(SYS_kill, __syscall(SYS_getpid), SIGKILL);
  24         }
  25         c->err = ret;
  26 }
  27
  28 int __setxid(int nr, int id, int eid, int sid)
  29 {
  30         /* err is initially nonzero so that failure of the first thread does not
  31          * trigger the safety kill above. */
  32         struct ctx c = { .nr = nr, .id = id, .eid = eid, .sid = sid, .err = -1 };
  33         __synccall(do_setxid, &c);
  34         if (c.err) {
  35                 if (c.err>0) errno = c.err;
  36                 return -1;
  37         }
  38         return 0;
  39 }