[PATCH] Return EPERM not ECHILD on security_task_wait failure

[Roland McGrath]

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 -EPERM instead of -ECHILD if some
children were ruled out solely because security_task_wait failed.

Signed-off-by: Roland McGrath <[EMAIL PROTECTED]>
---
 kernel/exit.c |   12 +++++++++++-
 1 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index f132349..a41052f 100644  
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1067,7 +1067,7 @@ static int eligible_child(pid_t pid, int
                return 2;
 
        if (security_task_wait(p))
-               return 0;
+               return -1;
 
        return 1;
 }
@@ -1449,6 +1449,7 @@ static long do_wait(pid_t pid, int optio
        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 +1458,7 @@ 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 +1474,12 @@ repeat:
                        if (!ret)
                                continue;
 
+                       if (unlikely(ret < 0)) {
+                               denied = 1;
+                               continue;
+                       }
+                       allowed = 1;
+
                        switch (p->state) {
                        case TASK_TRACED:
                                /*
@@ -1570,6 +1578,8 @@ check_continued:
                goto repeat;
        }
        retval = -ECHILD;
+       if (unlikely(denied) && !allowed)
+               retval = -EPERM;
 end:
        current->state = TASK_RUNNING;
        remove_wait_queue(&current->signal->wait_chldexit,&wait);
-
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