From: Joao Moreira <[email protected]>
The function flow_rule_alloc in net/core/flow_offload.c [2] gets an
unsigned int num_actions (line 10) and later traverses the actions in
the rule (line 24) setting hw.stats to FLOW_ACTION_HW_STATS_DONT_CARE.
Within the same file, the loop in the line 24 compares a signed int
(i) to an unsigned int (num_actions), and then uses i as an array
index. If an integer overflow happens, then the array within the loop
is wrongly indexed, causing a write out of bounds.
After checking with maintainers, it seems that the front-end caps the
maximum value of num_action, thus it is not possible to reach the given
write out of bounds, yet, still, to prevent disasters it is better to
fix the signedness here.
Similarly, also it is also good to ensure that an overflow won't happen
in net/netfilter/nf_tables_offload.c's function nft_flow_rule_create by
making the variable unsigned and ensuring that it returns an error if
its value reaches 256. The set limit value comes from discussions in the
mailing list where 256 was identified as a more than enough for the
frontend actions.
This issue was observed by the commit author while reviewing a write-up
regarding a CVE within the same subsystem [1].
1 - https://nickgregory.me/post/2022/03/12/cve-2022-25636/
Tks,
v2:
- Identify overflow by making num_actions unsigned and checking if it
reaches UINT_MAX instead of looking for its signedness.
v3:
- Avoid overflow by checking if num_actions reaches 256 (which is
enough) instead of UINT_MAX.
Joao Moreira (2):
Make loop indexes unsigned
Make num_actions unsigned
net/core/flow_offload.c | 4 ++--
net/netfilter/nf_tables_offload.c | 7 ++++++-
2 files changed, 8 insertions(+), 3 deletions(-)
--
2.42.0
From: Joao Moreira <[email protected]>
Both flow_rule_alloc and offload_action_alloc functions received an
unsigned num_actions parameters which are then operated within a loop.
The index of this loop is declared as a signed int. If it was possible
to pass a large enough num_actions to these functions, it would lead to
an out of bounds write.
After checking with maintainers, it was mentioned that front-end will
cap the num_actions value and that it is not possible to reach this
function with such a large number. Yet, for correctness, it is still
better to fix this.
This issue was observed by the commit author while reviewing a write-up
regarding a CVE within the same subsystem [1].
1 - https://nickgregory.me/post/2022/03/12/cve-2022-25636/
Signed-off-by: Joao Moreira <[email protected]>
---
net/core/flow_offload.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/core/flow_offload.c b/net/core/flow_offload.c
index bc5169482710..bc3f53a09d8f 100644
--- a/net/core/flow_offload.c
+++ b/net/core/flow_offload.c
@@ -10,7 +10,7 @@
struct flow_rule *flow_rule_alloc(unsigned int num_actions)
{
struct flow_rule *rule;
- int i;
+ unsigned int i;
rule = kzalloc(struct_size(rule, action.entries, num_actions),
GFP_KERNEL);
@@ -31,7 +31,7 @@ EXPORT_SYMBOL(flow_rule_alloc);
struct flow_offload_action *offload_action_alloc(unsigned int num_actions)
{
struct flow_offload_action *fl_action;
- int i;
+ unsigned int i;
fl_action = kzalloc(struct_size(fl_action, action.entries, num_actions),
GFP_KERNEL);
--
2.42.0
On Wed, Sep 27, 2023 at 09:47:14AM -0700, [email protected] wrote:
> From: Joao Moreira <[email protected]>
>
> Both flow_rule_alloc and offload_action_alloc functions received an
> unsigned num_actions parameters which are then operated within a loop.
> The index of this loop is declared as a signed int. If it was possible
> to pass a large enough num_actions to these functions, it would lead to
> an out of bounds write.
>
> After checking with maintainers, it was mentioned that front-end will
> cap the num_actions value and that it is not possible to reach this
> function with such a large number. Yet, for correctness, it is still
> better to fix this.
>
> This issue was observed by the commit author while reviewing a write-up
> regarding a CVE within the same subsystem [1].
>
> 1 - https://nickgregory.me/post/2022/03/12/cve-2022-25636/
>
> Signed-off-by: Joao Moreira <[email protected]>
> ---
> net/core/flow_offload.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/core/flow_offload.c b/net/core/flow_offload.c
> index bc5169482710..bc3f53a09d8f 100644
> --- a/net/core/flow_offload.c
> +++ b/net/core/flow_offload.c
> @@ -10,7 +10,7 @@
> struct flow_rule *flow_rule_alloc(unsigned int num_actions)
> {
> struct flow_rule *rule;
> - int i;
> + unsigned int i;
With the 2^8 cap, I don't think this patch is required anymore.
>
> rule = kzalloc(struct_size(rule, action.entries, num_actions),
> GFP_KERNEL);
> @@ -31,7 +31,7 @@ EXPORT_SYMBOL(flow_rule_alloc);
> struct flow_offload_action *offload_action_alloc(unsigned int num_actions)
> {
> struct flow_offload_action *fl_action;
> - int i;
> + unsigned int i;
>
> fl_action = kzalloc(struct_size(fl_action, action.entries, num_actions),
> GFP_KERNEL);
> --
> 2.42.0
>
On 2023-09-28 06:40, Pablo Neira Ayuso wrote:
> On Wed, Sep 27, 2023 at 09:47:14AM -0700, [email protected]
> wrote:
>> From: Joao Moreira <[email protected]>
>>
>> Both flow_rule_alloc and offload_action_alloc functions received an
>> unsigned num_actions parameters which are then operated within a loop.
>> The index of this loop is declared as a signed int. If it was possible
>> to pass a large enough num_actions to these functions, it would lead
>> to
>> an out of bounds write.
>>
>> After checking with maintainers, it was mentioned that front-end will
>> cap the num_actions value and that it is not possible to reach this
>> function with such a large number. Yet, for correctness, it is still
>> better to fix this.
>>
>> This issue was observed by the commit author while reviewing a
>> write-up
>> regarding a CVE within the same subsystem [1].
>>
>> 1 - https://nickgregory.me/post/2022/03/12/cve-2022-25636/
>>
>> Signed-off-by: Joao Moreira <[email protected]>
>> ---
>> net/core/flow_offload.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/core/flow_offload.c b/net/core/flow_offload.c
>> index bc5169482710..bc3f53a09d8f 100644
>> --- a/net/core/flow_offload.c
>> +++ b/net/core/flow_offload.c
>> @@ -10,7 +10,7 @@
>> struct flow_rule *flow_rule_alloc(unsigned int num_actions)
>> {
>> struct flow_rule *rule;
>> - int i;
>> + unsigned int i;
>
> With the 2^8 cap, I don't think this patch is required anymore.
Hm. While I understand that there is not a significant menace haunting
this... would it be good for (1) type correctness and (2) prevent that
things blow up if something changes and someone misses this spot?
>
>>
>> rule = kzalloc(struct_size(rule, action.entries, num_actions),
>> GFP_KERNEL);
>> @@ -31,7 +31,7 @@ EXPORT_SYMBOL(flow_rule_alloc);
>> struct flow_offload_action *offload_action_alloc(unsigned int
>> num_actions)
>> {
>> struct flow_offload_action *fl_action;
>> - int i;
>> + unsigned int i;
>>
>> fl_action = kzalloc(struct_size(fl_action, action.entries,
>> num_actions),
>> GFP_KERNEL);
>> --
>> 2.42.0
>>
On Thu, Sep 28, 2023 at 07:53:14PM -0700, Joao Moreira wrote:
> On 2023-09-28 06:40, Pablo Neira Ayuso wrote:
> > On Wed, Sep 27, 2023 at 09:47:14AM -0700, [email protected] wrote:
> > > From: Joao Moreira <[email protected]>
> > >
> > > Both flow_rule_alloc and offload_action_alloc functions received an
> > > unsigned num_actions parameters which are then operated within a loop.
> > > The index of this loop is declared as a signed int. If it was possible
> > > to pass a large enough num_actions to these functions, it would lead
> > > to
> > > an out of bounds write.
> > >
> > > After checking with maintainers, it was mentioned that front-end will
> > > cap the num_actions value and that it is not possible to reach this
> > > function with such a large number. Yet, for correctness, it is still
> > > better to fix this.
> > >
> > > This issue was observed by the commit author while reviewing a
> > > write-up
> > > regarding a CVE within the same subsystem [1].
> > >
> > > 1 - https://nickgregory.me/post/2022/03/12/cve-2022-25636/
> > >
> > > Signed-off-by: Joao Moreira <[email protected]>
> > > ---
> > > net/core/flow_offload.c | 4 ++--
> > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/net/core/flow_offload.c b/net/core/flow_offload.c
> > > index bc5169482710..bc3f53a09d8f 100644
> > > --- a/net/core/flow_offload.c
> > > +++ b/net/core/flow_offload.c
> > > @@ -10,7 +10,7 @@
> > > struct flow_rule *flow_rule_alloc(unsigned int num_actions)
> > > {
> > > struct flow_rule *rule;
> > > - int i;
> > > + unsigned int i;
> >
> > With the 2^8 cap, I don't think this patch is required anymore.
>
> Hm. While I understand that there is not a significant menace haunting
> this... would it be good for (1) type correctness and (2) prevent that
> things blow up if something changes and someone misses this spot?
Nothing is going to change, please remove unnecesary updates. Capping
to 2^8 for all hardware offload subsystems is sufficient by now. If
someone needs more than that, it will have to justify it.