linux-kernel - Re: [PATCH 1/1] mm: Prevent dereferencing non-allocated per

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20071127151241.038c146d.akpm@linux-foundation.org>
Date:	Tue, 27 Nov 2007 15:12:41 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	travis@....com, ak@...e.de, clameter@....com, pageexec@...email.hu,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mm: Prevent dereferencing non-allocated per_cpu
 variables

On Tue, 27 Nov 2007 23:16:28 +0100
Andi Kleen <andi@...stfloor.org> wrote:

> On Tue, Nov 27, 2007 at 01:50:53PM -0800, travis@....com wrote:
> > Change loops controlled by 'for (i = 0; i < NR_CPUS; i++)' to use
> > 'for_each_possible_cpu(i)' when there's a _remote possibility_ of
> > dereferencing a non-allocated per_cpu variable involved.
> > 
> > All files except mm/vmstat.c are x86 arch.
> > 
> > Based on 2.6.24-rc3-mm1 .
> > 
> > Thanks to pageexec@...email.hu for pointing this out.
> 
> Looks good to me. 2.6.24 candidate.

hm.  Has anyone any evidence that we're actually touching
not-possible-cpu's memory here?

Also, the sum_vm_events() change looks buggy - it assumes that
cpu_possible_map has no gaps in it.  But that change is unneeded because
sum_vm_events() is only ever passed cpu_online_map and I'm hoping that we
don't usually online not-possible CPUs.

--- a/mm/vmstat.c~mm-prevent-dereferencing-non-allocated-per_cpu-variables-fix
+++ a/mm/vmstat.c
@@ -27,12 +27,12 @@ static void sum_vm_events(unsigned long 
 	memset(ret, 0, NR_VM_EVENT_ITEMS * sizeof(unsigned long));
 
 	cpu = first_cpu(*cpumask);
-	while (cpu < NR_CPUS && cpu_possible(cpu)) {
+	while (cpu < NR_CPUS) {
 		struct vm_event_state *this = &per_cpu(vm_event_states, cpu);
 
 		cpu = next_cpu(cpu, *cpumask);
 
-		if (cpu < NR_CPUS && cpu_possible(cpu))
+		if (cpu < NR_CPUS)
 			prefetch(&per_cpu(vm_event_states, cpu));
 
 
_

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/