Re: + prctl-add-pr_set_proctitle_area-option.patch added to -mm tree

[Oleg Nesterov <oleg@redhat.com>]

@@ -1424,6 +1424,28 @@ static void k_getrusage(struct task_stru
 			} while (t != p);
 			break;
 
+		case PR_SET_PROCTITLE_AREA: {
+			struct mm_struct *mm = current->mm;
+			unsigned long addr = arg2;
+			unsigned long len = arg3;
+			unsigned long end = arg2 + arg3;
+
+			if (len > PAGE_SIZE)
+				return -EINVAL;
+
+			if (addr >= end)
+				return -EINVAL;
+
+			if (!access_ok(VERIFY_READ, addr, len))
+				return -EFAULT;
+
+			mutex_lock(&mm->arg_lock);
+			mm->arg_start = addr;
+			mm->arg_end = end;
+			mutex_unlock(&mm->arg_lock);

This looks like the merging error, I guess this code should go into
sys_prct(), not k_getrusage().


The patch adds mm_struct->arg_lock mutex. Can't we reuse mm->mmap_sem?
A bit ugly to have mm->arg_lock just to synchronize sys_prctl() and
proc_pid_cmdline(), imho.

Yes, we can't do access_process_vm() under ->mmap_sem, but we can add
the new helper, say, access_process_vm_locked(tsk, mm, ...) which does
the actual work. Then proc_pid_cmdline() can take mmap_sem for reading,
read arg_start/arg_end and call access_process_vm_locked().

No?

Oleg.