[patch] net_sched: stack info leak in cbq_dump_wrr()

[patch] net_sched: stack info leak in cbq_dump_wrr()

[Dan Carpenter]

opt.__reserved isn't cleared so we leak a byte of stack information.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
index 71a5688..6398a61 100644
--- a/net/sched/sch_cbq.c
+++ b/net/sched/sch_cbq.c
@@ -1469,6 +1469,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
 	opt.allot = cl->allot;
 	opt.priority = cl->priority + 1;
 	opt.cpriority = cl->cpriority + 1;
+	opt.__reserved = 0;
 	opt.weight = cl->weight;
 	if (nla_put(skb, TCA_CBQ_WRROPT, sizeof(opt), &opt))
 		goto nla_put_failure;

Re: [patch] net_sched: stack info leak in cbq_dump_wrr()

[Joe Perches]

On Mon, 2013-07-29 at 22:36 +0300, Dan Carpenter wrote:
> opt.__reserved isn't cleared so we leak a byte of stack information.
[]
> diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
[]
> @@ -1469,6 +1469,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
>  	opt.allot = cl->allot;
>  	opt.priority = cl->priority + 1;
>  	opt.cpriority = cl->cpriority + 1;
> +	opt.__reserved = 0;
>  	opt.weight = cl->weight;
>  	if (nla_put(skb, TCA_CBQ_WRROPT, sizeof(opt), &opt))
>  		goto nla_put_failure;

Alignment isn't guaranteed here so it'd
probably be better with a memset.

Re: [patch] net_sched: stack info leak in cbq_dump_wrr()

[Dan Carpenter]

On Mon, Jul 29, 2013 at 12:44:32PM -0700, Joe Perches wrote:
> On Mon, 2013-07-29 at 22:36 +0300, Dan Carpenter wrote:
> > opt.__reserved isn't cleared so we leak a byte of stack information.
> []
> > diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
> []
> > @@ -1469,6 +1469,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
> >  	opt.allot = cl->allot;
> >  	opt.priority = cl->priority + 1;
> >  	opt.cpriority = cl->cpriority + 1;
> > +	opt.__reserved = 0;
> >  	opt.weight = cl->weight;
> >  	if (nla_put(skb, TCA_CBQ_WRROPT, sizeof(opt), &opt))
> >  		goto nla_put_failure;
> 
> Alignment isn't guaranteed here so it'd
> probably be better with a memset.
> 

Hm...  Which arches would align it differently?

regards,
dan carpenter

Re: [patch] net_sched: stack info leak in cbq_dump_wrr()

[Joe Perches]

On Mon, 2013-07-29 at 23:01 +0300, Dan Carpenter wrote:
> On Mon, Jul 29, 2013 at 12:44:32PM -0700, Joe Perches wrote:
> > On Mon, 2013-07-29 at 22:36 +0300, Dan Carpenter wrote:
> > > opt.__reserved isn't cleared so we leak a byte of stack information.
> > []
> > > diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
> > []
> > > @@ -1469,6 +1469,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
> > >  	opt.allot = cl->allot;
> > >  	opt.priority = cl->priority + 1;
> > >  	opt.cpriority = cl->cpriority + 1;
> > > +	opt.__reserved = 0;
> > >  	opt.weight = cl->weight;
> > >  	if (nla_put(skb, TCA_CBQ_WRROPT, sizeof(opt), &opt))
> > >  		goto nla_put_failure;
> > 
> > Alignment isn't guaranteed here so it'd
> > probably be better with a memset.
> > 
> 
> Hm...  Which arches would align it differently?

Hey Dan.

None so far as I know, but what difference does it make
when it's a general correctness issue?

Re: [patch] net_sched: stack info leak in cbq_dump_wrr()

[David Miller]

From: Joe Perches <joe@perches.com>
Date: Mon, 29 Jul 2013 13:12:31 -0700

> On Mon, 2013-07-29 at 23:01 +0300, Dan Carpenter wrote:
>> On Mon, Jul 29, 2013 at 12:44:32PM -0700, Joe Perches wrote:
>> > On Mon, 2013-07-29 at 22:36 +0300, Dan Carpenter wrote:
>> > > opt.__reserved isn't cleared so we leak a byte of stack information.
>> > []
>> > > diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
>> > []
>> > > @@ -1469,6 +1469,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
>> > >  	opt.allot = cl->allot;
>> > >  	opt.priority = cl->priority + 1;
>> > >  	opt.cpriority = cl->cpriority + 1;
>> > > +	opt.__reserved = 0;
>> > >  	opt.weight = cl->weight;
>> > >  	if (nla_put(skb, TCA_CBQ_WRROPT, sizeof(opt), &opt))
>> > >  		goto nla_put_failure;
>> > 
>> > Alignment isn't guaranteed here so it'd
>> > probably be better with a memset.
>> > 
>> 
>> Hm...  Which arches would align it differently?
> 
> Hey Dan.
> 
> None so far as I know, but what difference does it make
> when it's a general correctness issue?

Should see if the compiler optimizes the spurious stores away,
and if not we can use an initializer.

Re: [patch] net_sched: stack info leak in cbq_dump_wrr()

[Jiri Pirko]

Mon, Jul 29, 2013 at 09:36:51PM CEST, dan.carpenter@oracle.com wrote:
>opt.__reserved isn't cleared so we leak a byte of stack information.
>
>Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
>
>diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
>index 71a5688..6398a61 100644
>--- a/net/sched/sch_cbq.c
>+++ b/net/sched/sch_cbq.c
>@@ -1469,6 +1469,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
> 	opt.allot = cl->allot;
> 	opt.priority = cl->priority + 1;
> 	opt.cpriority = cl->cpriority + 1;
>+	opt.__reserved = 0;

There's probably better to zero whole opt at the beginning of the function.

Re: [patch] net_sched: stack info leak in cbq_dump_wrr()

[Joe Perches]

On Mon, 2013-07-29 at 14:17 -0700, David Miller wrote:
> From: Joe Perches <joe@perches.com>
> Date: Mon, 29 Jul 2013 13:12:31 -0700
> 
> > On Mon, 2013-07-29 at 23:01 +0300, Dan Carpenter wrote:
> >> On Mon, Jul 29, 2013 at 12:44:32PM -0700, Joe Perches wrote:
> >> > On Mon, 2013-07-29 at 22:36 +0300, Dan Carpenter wrote:
> >> > > opt.__reserved isn't cleared so we leak a byte of stack information.
> >> > []
> >> > > diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
> >> > []
> >> > > @@ -1469,6 +1469,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
> >> > >          opt.allot = cl->allot;
> >> > >          opt.priority = cl->priority + 1;
> >> > >          opt.cpriority = cl->cpriority + 1;
> >> > > +        opt.__reserved = 0;
> >> > >          opt.weight = cl->weight;
> >> > >          if (nla_put(skb, TCA_CBQ_WRROPT, sizeof(opt), &opt))
> >> > >                  goto nla_put_failure;
> >> > 
> >> > Alignment isn't guaranteed here so it'd
> >> > probably be better with a memset.
> >> > 
> >> 
> >> Hm...  Which arches would align it differently?
> > 
> > Hey Dan.
> > 
> > None so far as I know, but what difference does it make
> > when it's a general correctness issue?
> 
> Should see if the compiler optimizes the spurious stores away,
> and if not we can use an initializer.

If the initializer is

	struct foo = {0};

then as far as I know, the compiler is free to 
not initialize any padding.

However, it looks like gcc 4.7 generates the same
code for this with or without the __aligned__ use.

(with gcc -O2 -S t.c)

$ cat t.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct foo {
	int a;
	char b __attribute__((__aligned__(256)));
	long c;
};

void init1(void)
{
	struct foo bar = {0};
	printf("%p\n", &bar);
}

void init2(void)
{
	struct foo bar;
	memset(&bar, 0, sizeof(bar));
	printf("%p\n", &bar);
}

Re: [patch] net_sched: stack info leak in cbq_dump_wrr()

[Dan Carpenter]

On Mon, Jul 29, 2013 at 01:12:31PM -0700, Joe Perches wrote:
> On Mon, 2013-07-29 at 23:01 +0300, Dan Carpenter wrote:
> > On Mon, Jul 29, 2013 at 12:44:32PM -0700, Joe Perches wrote:
> > > On Mon, 2013-07-29 at 22:36 +0300, Dan Carpenter wrote:
> > > > opt.__reserved isn't cleared so we leak a byte of stack information.
> > > []
> > > > diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
> > > []
> > > > @@ -1469,6 +1469,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
> > > >  	opt.allot = cl->allot;
> > > >  	opt.priority = cl->priority + 1;
> > > >  	opt.cpriority = cl->cpriority + 1;
> > > > +	opt.__reserved = 0;
> > > >  	opt.weight = cl->weight;
> > > >  	if (nla_put(skb, TCA_CBQ_WRROPT, sizeof(opt), &opt))
> > > >  		goto nla_put_failure;
> > > 
> > > Alignment isn't guaranteed here so it'd
> > > probably be better with a memset.
> > > 
> > 
> > Hm...  Which arches would align it differently?
> 
> Hey Dan.
> 
> None so far as I know, but what difference does it make
> when it's a general correctness issue?
> 

Because I would assume if these aren't aligned the same way we have
far more serious problems than just this one case.  It would change
the user space API and break network protocols.

regards,
dan carpenter

Re: [patch] net_sched: stack info leak in cbq_dump_wrr()

[Joe Perches]

On Tue, 2013-07-30 at 09:55 +0300, Dan Carpenter wrote:
> On Mon, Jul 29, 2013 at 01:12:31PM -0700, Joe Perches wrote:
> > On Mon, 2013-07-29 at 23:01 +0300, Dan Carpenter wrote:
> > > On Mon, Jul 29, 2013 at 12:44:32PM -0700, Joe Perches wrote:
> > > > On Mon, 2013-07-29 at 22:36 +0300, Dan Carpenter wrote:
> > > > > opt.__reserved isn't cleared so we leak a byte of stack information.
> > > > []
> > > > > diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
> > > > []
> > > > > @@ -1469,6 +1469,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
> > > > >  	opt.allot = cl->allot;
> > > > >  	opt.priority = cl->priority + 1;
> > > > >  	opt.cpriority = cl->cpriority + 1;
> > > > > +	opt.__reserved = 0;
> > > > >  	opt.weight = cl->weight;
> > > > >  	if (nla_put(skb, TCA_CBQ_WRROPT, sizeof(opt), &opt))
> > > > >  		goto nla_put_failure;
> > > > 
> > > > Alignment isn't guaranteed here so it'd
> > > > probably be better with a memset.
> > > > 
> > > 
> > > Hm...  Which arches would align it differently?
> > 
> > Hey Dan.
> > 
> > None so far as I know, but what difference does it make
> > when it's a general correctness issue?
> > 
> 
> Because I would assume if these aren't aligned the same way we have
> far more serious problems than just this one case.  It would change
> the user space API and break network protocols.

<shrug>

I didn't say it was necessary to be done here, I said it
was a correctness issue.  I still believe that's true.

The nla_put here is by structure, the struct is unpacked,
and it's local to the arch, not a particular endian type.

btw: to answer David's question, gcc 4.7 is smart enough
to elide resetting values when the struct is initialized
to 0 either with a memset or using {0}.

$ cat t.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct foo {
	int a;
	char b;
	long c;
};

void init1(void)
{
	struct foo bar = {0};
	bar.a = 1;
	bar.b = 2;
	bar.c = 3;
	printf("%p\n", &bar);
}

void init2(void)
{
	struct foo bar;
	memset(&bar, 0, sizeof(bar));
	bar.a = 1;
	bar.b = 2;
	bar.c = 3;
	printf("%p\n", &bar);

$ gcc -S -O2 t.c
$ cat t.s
	.file	"t.c"
	.section	.rodata.str1.1,"aMS",@progbits,1
.LC0:
	.string	"%p\n"
	.text
	.p2align 4,,15
	.globl	init1
	.type	init1, @function
init1:
.LFB60:
	.cfi_startproc
	subl	$44, %esp
	.cfi_def_cfa_offset 48
	leal	20(%esp), %eax
	movl	%eax, 8(%esp)
	movl	$.LC0, 4(%esp)
	movl	$1, (%esp)
	movl	$0, 24(%esp)
	movl	$1, 20(%esp)
	movb	$2, 24(%esp)
	movl	$3, 28(%esp)
	call	__printf_chk
	addl	$44, %esp
	.cfi_def_cfa_offset 4
	ret
	.cfi_endproc
.LFE60:
	.size	init1, .-init1
	.p2align 4,,15
	.globl	init2
	.type	init2, @function
init2:
.LFB61:
	.cfi_startproc
	subl	$44, %esp
	.cfi_def_cfa_offset 48
	leal	20(%esp), %eax
	movl	%eax, 8(%esp)
	movl	$.LC0, 4(%esp)
	movl	$1, (%esp)
	movl	$0, 24(%esp)
	movl	$1, 20(%esp)
	movb	$2, 24(%esp)
	movl	$3, 28(%esp)
	call	__printf_chk
	addl	$44, %esp
	.cfi_def_cfa_offset 4
	ret
	.cfi_endproc
.LFE61:
	.size	init2, .-init2
	.ident	"GCC: (Ubuntu/Linaro 4.7.3-1ubuntu1) 4.7.3"
	.section	.note.GNU-stack,"",@progbits

Re: [patch] net_sched: stack info leak in cbq_dump_wrr()

[David Miller]

From: Joe Perches <joe@perches.com>
Date: Tue, 30 Jul 2013 00:12:32 -0700

> On Tue, 2013-07-30 at 09:55 +0300, Dan Carpenter wrote:
>> On Mon, Jul 29, 2013 at 01:12:31PM -0700, Joe Perches wrote:
>> > On Mon, 2013-07-29 at 23:01 +0300, Dan Carpenter wrote:
>> > > On Mon, Jul 29, 2013 at 12:44:32PM -0700, Joe Perches wrote:
>> > > > On Mon, 2013-07-29 at 22:36 +0300, Dan Carpenter wrote:
>> > > > > opt.__reserved isn't cleared so we leak a byte of stack information.
>> > > > []
>> > > > > diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
>> > > > []
>> > > > > @@ -1469,6 +1469,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
>> > > > >  	opt.allot = cl->allot;
>> > > > >  	opt.priority = cl->priority + 1;
>> > > > >  	opt.cpriority = cl->cpriority + 1;
>> > > > > +	opt.__reserved = 0;
>> > > > >  	opt.weight = cl->weight;
>> > > > >  	if (nla_put(skb, TCA_CBQ_WRROPT, sizeof(opt), &opt))
>> > > > >  		goto nla_put_failure;
>> > > > 
>> > > > Alignment isn't guaranteed here so it'd
>> > > > probably be better with a memset.
>> > > > 
>> > > 
>> > > Hm...  Which arches would align it differently?
>> > 
>> > Hey Dan.
>> > 
>> > None so far as I know, but what difference does it make
>> > when it's a general correctness issue?
>> > 
>> 
>> Because I would assume if these aren't aligned the same way we have
>> far more serious problems than just this one case.  It would change
>> the user space API and break network protocols.
> 
> <shrug>
> 
> I didn't say it was necessary to be done here, I said it
> was a correctness issue.  I still believe that's true.
> 
> The nla_put here is by structure, the struct is unpacked,
> and it's local to the arch, not a particular endian type.
> 
> btw: to answer David's question, gcc 4.7 is smart enough
> to elide resetting values when the struct is initialized
> to 0 either with a memset or using {0}.

Ok, I've just commited the following, thanks everyone.

--------------------
>From a0db856a95a29efb1c23db55c02d9f0ff4f0db48 Mon Sep 17 00:00:00 2001
From: "David S. Miller" <davem@davemloft.net>
Date: Tue, 30 Jul 2013 00:16:21 -0700
Subject: [PATCH] net_sched: Fix stack info leak in cbq_dump_wrr().

Make sure the reserved fields, and padding (if any), are
fully initialized.

Based upon a patch by Dan Carpenter and feedback from
Joe Perches.

Signed-off-by: David S. Miller <davem@davemloft.net>
---
 net/sched/sch_cbq.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
index 71a5688..7a42c81 100644
--- a/net/sched/sch_cbq.c
+++ b/net/sched/sch_cbq.c
@@ -1465,6 +1465,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
 	unsigned char *b = skb_tail_pointer(skb);
 	struct tc_cbq_wrropt opt;
 
+	memset(&opt, 0, sizeof(opt));
 	opt.flags = 0;
 	opt.allot = cl->allot;
 	opt.priority = cl->priority + 1;
-- 
1.7.11.7

Re: [patch] net_sched: stack info leak in cbq_dump_wrr()

[walter harms]

Am 30.07.2013 09:18, schrieb David Miller:
> From: Joe Perches <joe@perches.com>
> Date: Tue, 30 Jul 2013 00:12:32 -0700
> 
>> On Tue, 2013-07-30 at 09:55 +0300, Dan Carpenter wrote:
>>> On Mon, Jul 29, 2013 at 01:12:31PM -0700, Joe Perches wrote:
>>>> On Mon, 2013-07-29 at 23:01 +0300, Dan Carpenter wrote:
>>>>> On Mon, Jul 29, 2013 at 12:44:32PM -0700, Joe Perches wrote:
>>>>>> On Mon, 2013-07-29 at 22:36 +0300, Dan Carpenter wrote:
>>>>>>> opt.__reserved isn't cleared so we leak a byte of stack information.
>>>>>> []
>>>>>>> diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
>>>>>> []
>>>>>>> @@ -1469,6 +1469,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
>>>>>>>  	opt.allot = cl->allot;
>>>>>>>  	opt.priority = cl->priority + 1;
>>>>>>>  	opt.cpriority = cl->cpriority + 1;
>>>>>>> +	opt.__reserved = 0;
>>>>>>>  	opt.weight = cl->weight;
>>>>>>>  	if (nla_put(skb, TCA_CBQ_WRROPT, sizeof(opt), &opt))
>>>>>>>  		goto nla_put_failure;
>>>>>>
>>>>>> Alignment isn't guaranteed here so it'd
>>>>>> probably be better with a memset.
>>>>>>
>>>>>
>>>>> Hm...  Which arches would align it differently?
>>>>
>>>> Hey Dan.
>>>>
>>>> None so far as I know, but what difference does it make
>>>> when it's a general correctness issue?
>>>>
>>>
>>> Because I would assume if these aren't aligned the same way we have
>>> far more serious problems than just this one case.  It would change
>>> the user space API and break network protocols.
>>
>> <shrug>
>>
>> I didn't say it was necessary to be done here, I said it
>> was a correctness issue.  I still believe that's true.
>>
>> The nla_put here is by structure, the struct is unpacked,
>> and it's local to the arch, not a particular endian type.
>>
>> btw: to answer David's question, gcc 4.7 is smart enough
>> to elide resetting values when the struct is initialized
>> to 0 either with a memset or using {0}.
> 
> Ok, I've just commited the following, thanks everyone.
> 
> --------------------
>>From a0db856a95a29efb1c23db55c02d9f0ff4f0db48 Mon Sep 17 00:00:00 2001
> From: "David S. Miller" <davem@davemloft.net>
> Date: Tue, 30 Jul 2013 00:16:21 -0700
> Subject: [PATCH] net_sched: Fix stack info leak in cbq_dump_wrr().
> 
> Make sure the reserved fields, and padding (if any), are
> fully initialized.
> 
> Based upon a patch by Dan Carpenter and feedback from
> Joe Perches.
> 
> Signed-off-by: David S. Miller <davem@davemloft.net>
> ---
>  net/sched/sch_cbq.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
> index 71a5688..7a42c81 100644
> --- a/net/sched/sch_cbq.c
> +++ b/net/sched/sch_cbq.c
> @@ -1465,6 +1465,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
>  	unsigned char *b = skb_tail_pointer(skb);
>  	struct tc_cbq_wrropt opt;
>  
> +	memset(&opt, 0, sizeof(opt));
>  	opt.flags = 0;
>  	opt.allot = cl->allot;
>  	opt.priority = cl->priority + 1;

You can remove opt.flags = 0; then :=)

re,
 wh