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

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Date:	Tue, 10 Nov 2009 18:04:53 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Bryan Donlan <bdonlan@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Timo Sirainen <tss@....fi>,
	Ulrich Drepper <drepper@...hat.com>,
	WANG Cong <xiyou.wangcong@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: + prctl-add-pr_set_proctitle_area-option.patch added to -mm
	tree

@@ -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.

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