[PATCH][2.4-rc1] fix side effects of the kmod/ptrace secfix

[Bernhard Kaindl <kaindl@telering.at>]

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On Fri, 25 Apr 2003, Andreas Gietl wrote:
> > system monitoring stuff this way(I've even heard shutdown is affected)
>
> i can confirm that shutdown (halt|reboot) does not work on my 2.4.21-rc1-ac1
> boxes. (gentoo + redhat).

Thanks for the info!

> But your patch does not seem to fix it.

Very interesting also, the two liner adressed only the well-known problems.
To fix the other not so well-known side effects, a real cleanup is the way
to go.

Can you try the attached cleanup patch instead of the two-liner?

It's an inital cleanup and should fix the other side effects which
I described in my mails.

Bernhard Kaindl

PS: If either patch is applied correctly, this

	su guest -c 'ps $PPID;wc -m </proc/$PPID/cmdline'

should give:

  PID TTY      STAT   TIME COMMAND
 2452 pts/2    S      0:00 su bin -c ps $PPID;wc -m </proc/$PPID/cmdline
     46

If it does not, access_process_vm is not fixed properly.

Second, calling this as root:

	strace -fewrite su -c /bin/echo 2>&1 | grep pid

should give:

[pid  2599] --- SIGSTOP (Stopped (signal)) @ 0 (0) ---
[pid  2599] write(1, "\n", 1

If it does not, ptrace_check_attach is not fixed properly.

(These are only the checks for the well known side
effects which should be fixed even with the short
is_dumpable() -> task_dumpable patch.)

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--- kernel/ptrace.c	2003/04/22 21:14:20	1.1
+++ kernel/ptrace.c	2003/04/25 06:21:16	1.3
@@ -21,9 +21,6 @@
  */
 int ptrace_check_attach(struct task_struct *child, int kill)
 {
-	mb();
-	if (!is_dumpable(child))
-		return -EPERM;
 
 	if (!(child->ptrace & PT_PTRACED))
 		return -ESRCH;
@@ -127,8 +124,6 @@ int access_process_vm(struct task_struct
 	/* Worry about races with exit() */
 	task_lock(tsk);
 	mm = tsk->mm;
-	if (!is_dumpable(tsk) || (&init_mm == mm))
-		mm = NULL;
 	if (mm)
 		atomic_inc(&mm->mm_users);
 	task_unlock(tsk);
--- kernel/sys.c	2003/04/25 06:23:15	1.1
+++ kernel/sys.c	2003/04/25 06:23:51
@@ -1252,8 +1252,7 @@ asmlinkage long sys_prctl(int option, un
 				error = -EINVAL;
 				break;
 			}
-			if (is_dumpable(current))
-				current->mm->dumpable = arg2;
+			current->mm->dumpable = arg2;
 			break;
 
 	        case PR_SET_UNALIGN: