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Message-ID: <6aab36aa.56337.18ca3c6af7a.Coremail.linma@zju.edu.cn> Date: Tue, 26 Dec 2023 09:39:16 +0800 (GMT+08:00) From: "Lin Ma" <linma@....edu.cn> To: "Jamal Hadi Salim" <jhs@...atatu.com> Cc: xiyou.wangcong@...il.com, jiri@...nulli.us, davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH net v1] net/sched: cls_api: complement tcf_tfilter_dump_policy Hello Jamal, > > Can you clarify what "heap data leak" you are referring to? > As much as i can see any reference to NLA_TCA_CHAIN is checked for > presence before being put to use. So far that reason I dont see how > this patch qualifies as "net". It looks like an enhancement to me > which should target net-next, unless i am missing something obvious. > Sure, thanks for your reply, (and merry Christmas :D). I didn't mention the detail as I consider the commit message in `5e2424708da7` could make a point. In short, the code ``` if (tca[TCA_CHAIN] && nla_get_u32(tca[TCA_CHAIN]) ``` only checks if the attribute TCA_CHAIN exists but never checks about the attribute length because that attribute is parsed by the function nlmsg_parse_deprecated which will parse an attribute even not described in the given policy (here, the tcf_tfilter_dump_policy). Moreover, the netlink message is allocated via netlink_alloc_large_skb (see net/netlink/af_netlink.c) that does not clear out the heap buffer. Hence a malicious user could send a malicious TCA_CHAIN attribute here without putting any payload and the above `nla_get_u32` could dereference a dirty data that is sprayed by the user. Other place gets TCA_CHAIN with provide policy rtm_tca_policy that has a description. ``` [TCA_CHAIN] = { .type = NLA_U32 }, ``` and this patch aims to do so. Unfortunately, I have not opened the exploit for CVE-2023-3773 (https://access.redhat.com/security/cve/cve-2023-3773) yet but the idea is similar and you can take it as an example. > cheers, > jamal > Regards Lin
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