ptrace fix changes output of ps ax

[Tachino Nobuhiro]

Hello, 

After 2.4.21-pre6, I found "ps ax" displays some processes
as the process names which are embraced with square brackets
like these.

1115 ?        S      0:00 [httpd]
1478 ?        S      0:00 [atd]

It is because proc_pid_cmdline() calls access_process_vm() and it fails.
The patch below fixes the problem. With this patch, access_process_vm()
do not reject requests if the access is read only.

I'm not certain this is right fix, but at least I confirmed
isec-ptrace-kmot-exploit cannot get root privilege with this patch.

Please comment.

diff -Nur linux-2.4.org/kernel/ptrace.c linux-2.4/kernel/ptrace.c
--- linux-2.4.org/kernel/ptrace.c	2003-03-28 15:59:15.000000000 +0900
+++ linux-2.4/kernel/ptrace.c	2003-04-03 16:04:32.000000000 +0900
@@ -140,7 +140,7 @@
 	/* Worry about races with exit() */
 	task_lock(tsk);
 	mm = tsk->mm;
-	if (!is_dumpable(tsk) || (&init_mm == mm))
+	if ((!is_dumpable(tsk) || (&init_mm == mm)) && write)
 		mm = NULL;
 	if (mm)
 		atomic_inc(&mm->mm_users);