Re: [PATCH 13/18] ipv6: prevent bounds-check bypass via speculative execution

[Dan Williams]

On Sat, Jan 6, 2018 at 6:48 AM, Stephen Hemminger
<stephen@xxxxxxxxxxxxxxxxxx> wrote:
> On Fri, 05 Jan 2018 17:11:04 -0800
> Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
>
>> Static analysis reports that 'offset' may be a user controlled value
>> that is used as a data dependency reading from a raw6_frag_vec buffer.
>> In order to avoid potential leaks of kernel memory values, block
>> speculative execution of the instruction stream that could issue further
>> reads based on an invalid '*(rfv->c + offset)' value.
>>
>> Based on an original patch by Elena Reshetova.
>>
>> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
>> Cc: Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx>
>> Cc: Hideaki YOSHIFUJI <yoshfuji@xxxxxxxxxxxxxx>
>> Cc: netdev@xxxxxxxxxxxxxxx
>> Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
>> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
>> ---
>>  net/ipv6/raw.c |    9 +++++----
>>  1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
>> index 761a473a07c5..384e3d59d148 100644
>> --- a/net/ipv6/raw.c
>> +++ b/net/ipv6/raw.c
>> @@ -33,6 +33,7 @@
>>  #include <linux/skbuff.h>
>>  #include <linux/compat.h>
>>  #include <linux/uaccess.h>
>> +#include <linux/compiler.h>
>>  #include <asm/ioctls.h>
>>
>>  #include <net/net_namespace.h>
>> @@ -725,17 +726,17 @@ static int raw6_getfrag(void *from, char *to, int offset, int len, int odd,
>>                      struct sk_buff *skb)
>>  {
>>       struct raw6_frag_vec *rfv = from;
>> +     char *rfv_buf;
>>
>> -     if (offset < rfv->hlen) {
>> +     if ((rfv_buf = nospec_array_ptr(rfv->c, offset, rfv->hlen))) {
>>               int copy = min(rfv->hlen - offset, len);
>
> Minor nit.
>
> Please don't do assignment in condition test here.
> Instead.
>         rfv_buf = nospec_array_ptr(rfv->c, offset, rfv->hlen);
>         if (rfv_buf) {

Yeah, sorry about that. This was a hold over from an earlier version
where nospec_array_ptr() did not include the necessary barrier and we
relied on a new if_nospec helper, but now that if_nospec is no longer
being proposed I can go back and clean this up.