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
checking that num_actions is not negative.
Tks,
Joao Moreira (2):
Make loop indexes unsigned
Ensure num_actions is not a negative
net/core/flow_offload.c | 4 ++--
net/netfilter/nf_tables_offload.c | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)
--
2.41.0
On 2023-08-31 18:28, Jakub Kicinski wrote:
> On Thu, 31 Aug 2023 18:04:35 -0700 [email protected] wrote:
>> 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.
>
> How did you find this? The commit messages should include info
> about how the issue was discovered.
Sure, I'll wait a bit longer for more suggestions and add the info in a
next patch version.
Meanwhile, fwiiw, I stumbled on the bug when I was reading Nick
Gregory's write-up on CVE-2022-25636 [1], which happens nearby but is
not exactly this issue.
Tks,
Joao
[1] - https://nickgregory.me/post/2022/03/12/cve-2022-25636/
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.
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);
--
2.41.0
On Thu, 31 Aug 2023 18:04:35 -0700 [email protected] wrote:
> 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.
How did you find this? The commit messages should include info
about how the issue was discovered.
--
pw-bot: cr