[PATCH v2 2/2] net: openvswitch: Annotate struct mask_array with __counted_by

[PATCH v2 2/2] net: openvswitch: Annotate struct mask_array with __counted_by

[Christophe JAILLET]

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
v2: Fix the subject  [Ilya Maximets]
    fix the field name used with __counted_by  [Ilya Maximets]

v1: https://lore.kernel.org/all/f66ddcf1ef9328f10292ea75a17b584359b6cde3.1696156198.git.christophe.jaillet@wanadoo.fr/


This patch is part of a work done in parallel of what is currently worked
on by Kees Cook.

My patches are only related to corner cases that do NOT match the
semantic of his Coccinelle script[1].

In this case, in tbl_mask_array_alloc(), several things are allocated with
a single allocation. Then, some pointer arithmetic computes the address of
the memory after the flex-array.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
---
 net/openvswitch/flow_table.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/openvswitch/flow_table.h b/net/openvswitch/flow_table.h
index 9e659db78c05..f524dc3e4862 100644
--- a/net/openvswitch/flow_table.h
+++ b/net/openvswitch/flow_table.h
@@ -48,7 +48,7 @@ struct mask_array {
 	int count, max;
 	struct mask_array_stats __percpu *masks_usage_stats;
 	u64 *masks_usage_zero_cntr;
-	struct sw_flow_mask __rcu *masks[];
+	struct sw_flow_mask __rcu *masks[] __counted_by(max);
 };
 
 struct table_instance {
-- 
2.34.1

Re: [PATCH v2 2/2] net: openvswitch: Annotate struct mask_array with __counted_by

[Kees Cook]

On Sat, Oct 14, 2023 at 08:34:53AM +0200, Christophe JAILLET wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> ---
> v2: Fix the subject  [Ilya Maximets]
>     fix the field name used with __counted_by  [Ilya Maximets]
> 
> v1: https://lore.kernel.org/all/f66ddcf1ef9328f10292ea75a17b584359b6cde3.1696156198.git.christophe.jaillet@wanadoo.fr/
> 
> 
> This patch is part of a work done in parallel of what is currently worked
> on by Kees Cook.
> 
> My patches are only related to corner cases that do NOT match the
> semantic of his Coccinelle script[1].
> 
> In this case, in tbl_mask_array_alloc(), several things are allocated with
> a single allocation. Then, some pointer arithmetic computes the address of
> the memory after the flex-array.
> 
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> ---
>  net/openvswitch/flow_table.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/openvswitch/flow_table.h b/net/openvswitch/flow_table.h
> index 9e659db78c05..f524dc3e4862 100644
> --- a/net/openvswitch/flow_table.h
> +++ b/net/openvswitch/flow_table.h
> @@ -48,7 +48,7 @@ struct mask_array {
>  	int count, max;
>  	struct mask_array_stats __percpu *masks_usage_stats;
>  	u64 *masks_usage_zero_cntr;
> -	struct sw_flow_mask __rcu *masks[];
> +	struct sw_flow_mask __rcu *masks[] __counted_by(max);
>  };

Yup, this looks correct to me. Thanks!

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

Re: [PATCH v2 2/2] net: openvswitch: Annotate struct mask_array with __counted_by

[Julia Lawall]

On Sat, 14 Oct 2023, Kees Cook wrote:

> On Sat, Oct 14, 2023 at 08:34:53AM +0200, Christophe JAILLET wrote:
> > Prepare for the coming implementation by GCC and Clang of the __counted_by
> > attribute. Flexible array members annotated with __counted_by can have
> > their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> > (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> > functions).
> >
> > Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> > ---
> > v2: Fix the subject  [Ilya Maximets]
> >     fix the field name used with __counted_by  [Ilya Maximets]
> >
> > v1: https://lore.kernel.org/all/f66ddcf1ef9328f10292ea75a17b584359b6cde3.1696156198.git.christophe.jaillet@wanadoo.fr/
> >
> >
> > This patch is part of a work done in parallel of what is currently worked
> > on by Kees Cook.
> >
> > My patches are only related to corner cases that do NOT match the
> > semantic of his Coccinelle script[1].

What was the problem with the semantic patch in this case?

thanks,
julia


> >
> > In this case, in tbl_mask_array_alloc(), several things are allocated with
> > a single allocation. Then, some pointer arithmetic computes the address of
> > the memory after the flex-array.
> >
> > [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> > ---
> >  net/openvswitch/flow_table.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/openvswitch/flow_table.h b/net/openvswitch/flow_table.h
> > index 9e659db78c05..f524dc3e4862 100644
> > --- a/net/openvswitch/flow_table.h
> > +++ b/net/openvswitch/flow_table.h
> > @@ -48,7 +48,7 @@ struct mask_array {
> >  	int count, max;
> >  	struct mask_array_stats __percpu *masks_usage_stats;
> >  	u64 *masks_usage_zero_cntr;
> > -	struct sw_flow_mask __rcu *masks[];
> > +	struct sw_flow_mask __rcu *masks[] __counted_by(max);
> >  };
>
> Yup, this looks correct to me. Thanks!
>
> Reviewed-by: Kees Cook <keescook@chromium.org>
>
> --
> Kees Cook
>

Re: [PATCH v2 2/2] net: openvswitch: Annotate struct mask_array with __counted_by

[Christophe JAILLET]

Le 15/10/2023 à 06:53, Julia Lawall a écrit :
> 
> 
> On Sat, 14 Oct 2023, Kees Cook wrote:
> 
>> On Sat, Oct 14, 2023 at 08:34:53AM +0200, Christophe JAILLET wrote:
>>> Prepare for the coming implementation by GCC and Clang of the __counted_by
>>> attribute. Flexible array members annotated with __counted_by can have
>>> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
>>> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
>>> functions).
>>>
>>> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
>>> ---
>>> v2: Fix the subject  [Ilya Maximets]
>>>      fix the field name used with __counted_by  [Ilya Maximets]
>>>
>>> v1: https://lore.kernel.org/all/f66ddcf1ef9328f10292ea75a17b584359b6cde3.1696156198.git.christophe.jaillet@wanadoo.fr/
>>>
>>>
>>> This patch is part of a work done in parallel of what is currently worked
>>> on by Kees Cook.
>>>
>>> My patches are only related to corner cases that do NOT match the
>>> semantic of his Coccinelle script[1].
> 
> What was the problem with the semantic patch in this case?


The allocation in tbl_mask_array_alloc() looks like:
	new = kzalloc(sizeof(struct mask_array) +
		      sizeof(struct sw_flow_mask *) * size +
		      sizeof(u64) * size, GFP_KERNEL);


We allocated the struct, the ending flex aray *and* some more memory at 
the same time.

IIUC the cocci script, this extra space is not taken into account with 
the current script and it won't match.

CJ


> 
> thanks,
> julia
> 
> 
>>>
>>> In this case, in tbl_mask_array_alloc(), several things are allocated with
>>> a single allocation. Then, some pointer arithmetic computes the address of
>>> the memory after the flex-array.
>>>
>>> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
>>> ---
>>>   net/openvswitch/flow_table.h | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/net/openvswitch/flow_table.h b/net/openvswitch/flow_table.h
>>> index 9e659db78c05..f524dc3e4862 100644
>>> --- a/net/openvswitch/flow_table.h
>>> +++ b/net/openvswitch/flow_table.h
>>> @@ -48,7 +48,7 @@ struct mask_array {
>>>   	int count, max;
>>>   	struct mask_array_stats __percpu *masks_usage_stats;
>>>   	u64 *masks_usage_zero_cntr;
>>> -	struct sw_flow_mask __rcu *masks[];
>>> +	struct sw_flow_mask __rcu *masks[] __counted_by(max);
>>>   };
>>
>> Yup, this looks correct to me. Thanks!
>>
>> Reviewed-by: Kees Cook <keescook@chromium.org>
>>
>> --
>> Kees Cook
>>
> 

Re: [ovs-dev] [PATCH v2 2/2] net: openvswitch: Annotate struct mask_array with __counted_by

[Simon Horman]

On Sat, Oct 14, 2023 at 07:29:57PM -0700, Kees Cook wrote:
> On Sat, Oct 14, 2023 at 08:34:53AM +0200, Christophe JAILLET wrote:
> > Prepare for the coming implementation by GCC and Clang of the __counted_by
> > attribute. Flexible array members annotated with __counted_by can have
> > their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> > (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> > functions).
> > 
> > Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> > ---
> > v2: Fix the subject  [Ilya Maximets]
> >     fix the field name used with __counted_by  [Ilya Maximets]
> > 
> > v1: https://lore.kernel.org/all/f66ddcf1ef9328f10292ea75a17b584359b6cde3.1696156198.git.christophe.jaillet@wanadoo.fr/
> > 
> > 
> > This patch is part of a work done in parallel of what is currently worked
> > on by Kees Cook.
> > 
> > My patches are only related to corner cases that do NOT match the
> > semantic of his Coccinelle script[1].
> > 
> > In this case, in tbl_mask_array_alloc(), several things are allocated with
> > a single allocation. Then, some pointer arithmetic computes the address of
> > the memory after the flex-array.
> > 
> > [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> > ---
> >  net/openvswitch/flow_table.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/net/openvswitch/flow_table.h b/net/openvswitch/flow_table.h
> > index 9e659db78c05..f524dc3e4862 100644
> > --- a/net/openvswitch/flow_table.h
> > +++ b/net/openvswitch/flow_table.h
> > @@ -48,7 +48,7 @@ struct mask_array {
> >  	int count, max;
> >  	struct mask_array_stats __percpu *masks_usage_stats;
> >  	u64 *masks_usage_zero_cntr;
> > -	struct sw_flow_mask __rcu *masks[];
> > +	struct sw_flow_mask __rcu *masks[] __counted_by(max);
> >  };
> 
> Yup, this looks correct to me. Thanks!
> 
> Reviewed-by: Kees Cook <keescook@chromium.org>
> 

Likewise, I agree this is correct.

Reviewed-by: Simon Horman <horms@kernel.org>