Re: [PATCH 0/2] Prevent potential write out of bounds

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On 2023-08-31 18:28, Jakub Kicinski wrote:
On Thu, 31 Aug 2023 18:04:35 -0700 joao@xxxxxxxxxxxxxxxxxx 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.


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