do_wait: fix sys_waitid()-specific behaviour
Vitaly Mayatskikh [Wed, 23 Sep 2009 22:56:51 +0000 (15:56 -0700)]
do_wait() checks ->wo_info to figure out who is the caller.  If it's not
NULL the caller should be sys_waitid(), in that case do_wait() fixes up
the retval or zeros ->wo_info, depending on retval from underlying
function.

This is bug: user can pass ->wo_info == NULL and sys_waitid() will return
incorrect value.

man 2 waitid says:

waitid(): returns 0 on success

Test-case:

int main(void)
{
if (fork())
assert(waitid(P_ALL, 0, NULL, WEXITED) == 0);

return 0;
}

Result:

Assertion `waitid(P_ALL, 0, ((void *)0), 4) == 0' failed.

Move that code to sys_waitid().

User-visible change: sys_waitid() will return 0 on success, either
infop is set or not.

Note, there's another bug in wait_noreap_copyout() which affects
return value of sys_waitid(). It will be fixed in next patch.

Signed-off-by: Vitaly Mayatskikh <v.mayatskih@gmail.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/exit.c

index 1daa7f4..2cc69eb 100644 (file)
@@ -1645,32 +1645,6 @@ notask:
 end:
        __set_current_state(TASK_RUNNING);
        remove_wait_queue(&current->signal->wait_chldexit, &wo->child_wait);
-
-       if (wo->wo_info) {
-               struct siginfo __user *infop = wo->wo_info;
-
-               if (retval > 0)
-                       retval = 0;
-               else {
-                       /*
-                        * For a WNOHANG return, clear out all the fields
-                        * we would set so the user can easily tell the
-                        * difference.
-                        */
-                       if (!retval)
-                               retval = put_user(0, &infop->si_signo);
-                       if (!retval)
-                               retval = put_user(0, &infop->si_errno);
-                       if (!retval)
-                               retval = put_user(0, &infop->si_code);
-                       if (!retval)
-                               retval = put_user(0, &infop->si_pid);
-                       if (!retval)
-                               retval = put_user(0, &infop->si_uid);
-                       if (!retval)
-                               retval = put_user(0, &infop->si_status);
-               }
-       }
        return retval;
 }
 
@@ -1715,6 +1689,29 @@ SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
        wo.wo_stat      = NULL;
        wo.wo_rusage    = ru;
        ret = do_wait(&wo);
+
+       if (ret > 0) {
+               ret = 0;
+       } else if (infop) {
+               /*
+                * For a WNOHANG return, clear out all the fields
+                * we would set so the user can easily tell the
+                * difference.
+                */
+               if (!ret)
+                       ret = put_user(0, &infop->si_signo);
+               if (!ret)
+                       ret = put_user(0, &infop->si_errno);
+               if (!ret)
+                       ret = put_user(0, &infop->si_code);
+               if (!ret)
+                       ret = put_user(0, &infop->si_pid);
+               if (!ret)
+                       ret = put_user(0, &infop->si_uid);
+               if (!ret)
+                       ret = put_user(0, &infop->si_status);
+       }
+
        put_pid(pid);
 
        /* avoid REGPARM breakage on x86: */