From: Joao Moreira <joao.moreira@xxxxxxxxx> 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
