Previously, one-element and zero-length arrays were treated as true
flexible arrays, even though they are actually "fake" flex arrays.
The __randomize_layout would leave them untouched at the end of the
struct, similarly to proper C99 flex-array members.
However, this approach changed with commit 1ee60356c2dc ("gcc-plugins:
randstruct: Only warn about true flexible arrays"). Now, only C99
flexible-array members will remain untouched at the end of the struct,
while one-element and zero-length arrays will be subject to randomization.
Fix a `__randomize_layout` crash in `struct neighbour` by transforming
zero-length array `primary_key` into a proper C99 flexible-array member.
Fixes: 1ee60356c2dc ("gcc-plugins: randstruct: Only warn about true flexible arrays")
Closes: https://lore.kernel.org/linux-hardening/[email protected]/
Signed-off-by: Gustavo A. R. Silva <[email protected]>
---
include/net/neighbour.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 07022bb0d44d..0d28172193fa 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -162,7 +162,7 @@ struct neighbour {
struct rcu_head rcu;
struct net_device *dev;
netdevice_tracker dev_tracker;
- u8 primary_key[0];
+ u8 primary_key[];
} __randomize_layout;
struct neigh_ops {
--
2.34.1
On Sat, Nov 25, 2023 at 03:33:58PM -0600, Gustavo A. R. Silva wrote:
> Previously, one-element and zero-length arrays were treated as true
> flexible arrays, even though they are actually "fake" flex arrays.
> The __randomize_layout would leave them untouched at the end of the
> struct, similarly to proper C99 flex-array members.
>
> However, this approach changed with commit 1ee60356c2dc ("gcc-plugins:
> randstruct: Only warn about true flexible arrays"). Now, only C99
> flexible-array members will remain untouched at the end of the struct,
> while one-element and zero-length arrays will be subject to randomization.
>
> Fix a `__randomize_layout` crash in `struct neighbour` by transforming
> zero-length array `primary_key` into a proper C99 flexible-array member.
>
> Fixes: 1ee60356c2dc ("gcc-plugins: randstruct: Only warn about true flexible arrays")
> Closes: https://lore.kernel.org/linux-hardening/[email protected]/
> Signed-off-by: Gustavo A. R. Silva <[email protected]>
Yes, please. Do we have any other 0-sized arrays hiding out in the
kernel? We need to get these all cleared...
Reviewed-by: Kees Cook <[email protected]>
--
Kees Cook
On 11/27/23 18:29, Kees Cook wrote:
> On Sat, Nov 25, 2023 at 03:33:58PM -0600, Gustavo A. R. Silva wrote:
>> Previously, one-element and zero-length arrays were treated as true
>> flexible arrays, even though they are actually "fake" flex arrays.
>> The __randomize_layout would leave them untouched at the end of the
>> struct, similarly to proper C99 flex-array members.
>>
>> However, this approach changed with commit 1ee60356c2dc ("gcc-plugins:
>> randstruct: Only warn about true flexible arrays"). Now, only C99
>> flexible-array members will remain untouched at the end of the struct,
>> while one-element and zero-length arrays will be subject to randomization.
>>
>> Fix a `__randomize_layout` crash in `struct neighbour` by transforming
>> zero-length array `primary_key` into a proper C99 flexible-array member.
>>
>> Fixes: 1ee60356c2dc ("gcc-plugins: randstruct: Only warn about true flexible arrays")
>> Closes: https://lore.kernel.org/linux-hardening/[email protected]/
>> Signed-off-by: Gustavo A. R. Silva <[email protected]>
>
> Yes, please. Do we have any other 0-sized arrays hiding out in the
> kernel? We need to get these all cleared...
I've found 27 instances of zero-length fake-flex arrays in next-20231127.
I'll send a patch series to transform all of them.
>
> Reviewed-by: Kees Cook <[email protected]>
>
Thanks!
--
Gustavo
Hi,
On Sat, Nov 25, 2023 at 03:33:58PM -0600, Gustavo A. R. Silva wrote:
> Previously, one-element and zero-length arrays were treated as true
> flexible arrays, even though they are actually "fake" flex arrays.
> The __randomize_layout would leave them untouched at the end of the
> struct, similarly to proper C99 flex-array members.
>
> However, this approach changed with commit 1ee60356c2dc ("gcc-plugins:
> randstruct: Only warn about true flexible arrays"). Now, only C99
> flexible-array members will remain untouched at the end of the struct,
> while one-element and zero-length arrays will be subject to randomization.
>
> Fix a `__randomize_layout` crash in `struct neighbour` by transforming
> zero-length array `primary_key` into a proper C99 flexible-array member.
>
> Fixes: 1ee60356c2dc ("gcc-plugins: randstruct: Only warn about true flexible arrays")
> Closes: https://lore.kernel.org/linux-hardening/[email protected]/
> Signed-off-by: Gustavo A. R. Silva <[email protected]>
> ---
> include/net/neighbour.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/net/neighbour.h b/include/net/neighbour.h
> index 07022bb0d44d..0d28172193fa 100644
> --- a/include/net/neighbour.h
> +++ b/include/net/neighbour.h
> @@ -162,7 +162,7 @@ struct neighbour {
> struct rcu_head rcu;
> struct net_device *dev;
> netdevice_tracker dev_tracker;
> - u8 primary_key[0];
> + u8 primary_key[];
> } __randomize_layout;
>
> struct neigh_ops {
Fixes the crash for me!
Tested-by: Joey Gouly <[email protected]>
>> diff --git a/include/net/neighbour.h b/include/net/neighbour.h
>> index 07022bb0d44d..0d28172193fa 100644
>> --- a/include/net/neighbour.h
>> +++ b/include/net/neighbour.h
>> @@ -162,7 +162,7 @@ struct neighbour {
>> struct rcu_head rcu;
>> struct net_device *dev;
>> netdevice_tracker dev_tracker;
>> - u8 primary_key[0];
>> + u8 primary_key[];
>> } __randomize_layout;
>>
>> struct neigh_ops {
>
> Fixes the crash for me!
Awesome. :)
--
Gustavo