Return EPERM not ECHILD on security_task_wait failure

wait* syscalls return -ECHILD even when an individual PID of a live child
was requested explicitly, when security_task_wait denies the operation.
This means that something like a broken SELinux policy can produce an
unexpected failure that looks just like a bug with wait or ptrace or
something.

This patch makes do_wait return -EACCES (or other appropriate error returned
from security_task_wait() instead of -ECHILD if some children were ruled out
solely because security_task_wait failed.

[jmorris@namei.org: switch error code to EACCES]
Signed-off-by: Roland McGrath <roland@redhat.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 2 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index b55ed4cc9104..92369240d91d 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1033,6 +1033,8 @@ asmlinkage void sys_exit_group(int error_code)
 
 static int eligible_child(pid_t pid, int options, struct task_struct *p)
 {
+        int err;
+
         if (pid > 0) {
                 if (p->pid != pid)
                         return 0;
@@ -1066,8 +1068,9 @@ static int eligible_child(pid_t pid, int options, struct task_struct *p)
         if (delay_group_leader(p))
                 return 2;
 
-        if (security_task_wait(p))
-                return 0;
+        err = security_task_wait(p);
+        if (err)
+                return err;
 
         return 1;
 }
@@ -1449,6 +1452,7 @@ static long do_wait(pid_t pid, int options, struct siginfo __user *infop,
         DECLARE_WAITQUEUE(wait, current);
         struct task_struct *tsk;
         int flag, retval;
+        int allowed, denied;
 
         add_wait_queue(&current->signal->wait_chldexit,&wait);
 repeat:
@@ -1457,6 +1461,7 @@ repeat:
          * match our criteria, even if we are not able to reap it yet.
          */
         flag = 0;
+        allowed = denied = 0;
         current->state = TASK_INTERRUPTIBLE;
         read_lock(&tasklist_lock);
         tsk = current;
@@ -1472,6 +1477,12 @@ repeat:
                         if (!ret)
                                 continue;
 
+                        if (unlikely(ret < 0)) {
+                                denied = ret;
+                                continue;
+                        }
+                        allowed = 1;
+
                         switch (p->state) {
                         case TASK_TRACED:
                                 /*
@@ -1570,6 +1581,8 @@ check_continued:
                 goto repeat;
         }
         retval = -ECHILD;
+        if (unlikely(denied) && !allowed)
+                retval = denied;
 end:
         current->state = TASK_RUNNING;
         remove_wait_queue(&current->signal->wait_chldexit,&wait);