lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Message-ID: <20221004170400.52c97523@kernel.org> Date: Tue, 4 Oct 2022 17:04:00 -0700 From: Jakub Kicinski <kuba@...nel.org> To: Kees Cook <keescook@...omium.org> Cc: Dmitry Vyukov <dvyukov@...gle.com>, syzbot <syzbot+3a080099974c271cd7e9@...kaller.appspotmail.com>, bpf@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com, fw@...len.de, harshit.m.mogalapalli@...cle.com, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, pabeni@...hat.com, syzkaller-bugs@...glegroups.com, linux-hardening@...r.kernel.org Subject: Re: [syzbot] upstream boot error: WARNING in netlink_ack On Tue, 4 Oct 2022 16:40:32 -0700 Kees Cook wrote: > On Tue, Oct 04, 2022 at 10:42:53AM -0700, Jakub Kicinski wrote: > > This has been weighing on my conscience a little, I don't like how we > > still depend on putting one length in the skb and then using a > > different one for the actual memcpy(). How would you feel about this > > patch on top (untested): > > tl;dr: yes, I like it. Please add a nlmsg_contents member. :) Can do, but you'll need to tell me how.. __DECLARE_FLEX_ARRAY(char, nlmsg_contents) ? > > + u32 size) > > +{ > > + if (unlikely(skb_tailroom(skb) < NLMSG_ALIGN(size))) > > + return NULL; > > + > > + if (!__builtin_constant_p(size) || NLMSG_ALIGN(size) - size != 0) > > why does a fixed size mean no memset? Copy and paste, it seems to originate from: 0c19b0adb8dd ("netlink: avoid memset of 0 bytes sparse warning") Any idea why sparse would not like empty memsets? > > rep = nlmsg_put(skb, NETLINK_CB(in_skb).portid, nlh->nlmsg_seq, > > - NLMSG_ERROR, payload, flags); > > + NLMSG_ERROR, sizeof(*errmsg), flags); > > + if (!rep) > > + goto err_bad_put; > > errmsg = nlmsg_data(rep); > > errmsg->error = err; > > - unsafe_memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg) > > - ? nlh->nlmsg_len : sizeof(*nlh), > > - /* Bounds checked by the skb layer. */); > > + memcpy(&errmsg->msg, nlh, sizeof(*nlh)); > > + > > + if (!(flags & NLM_F_CAPPED)) { > > Should it test this flag, or test if the sizes show the need for "extra" > payload length? > > I always found the progression of sizes here to be confusing. "payload" > starts as sizeof(*errmsg), and gets nlmsg_len(nlh) added but only when if > "(err && !(nlk->flags & NETLINK_F_CAP_ACK)" was true. struct nlmsgerr is one of the least badly documented structs we have in netlink so let me start with a copy & paste: struct nlmsgerr { int error; struct nlmsghdr msg; /* * followed by the message contents unless NETLINK_CAP_ACK was set * or the ACK indicates success (error == 0) * message length is aligned with NLMSG_ALIGN() */ /* * followed by TLVs defined in enum nlmsgerr_attrs * if NETLINK_EXT_ACK was set */ }; *Why* that's the behavior - 🤷 > Why is nlmsg_len(nlh) _wrong_ if the rest of its contents are > correct? This is an ack message, to be clear, doesn't mean anything was wrong. It just carries errno. > If this was "0" in the other state, the logic would just be: > > nlh_bytes = nlmsg_len(nlh); > total = sizeof(*errmsg); > total += nlh_bytes; > total += tlvlen; > > and: > > nlmsg_new(total, ...); > ... nlmsg_put(..., sizeof(*errmsg), ...); > ... > errmsg->error = err; > errmsg->nlh = *nlh; > if (nlh_bytes) { > data = nlmsg_append(..., nlh_bytes), ...); > ... > memcpy(data, nlh->nlmsg_contents, nlh_bytes); > } > > > + size_t data_len = nlh->nlmsg_len - sizeof(*nlh); > > I think data_len here is also "payload - sizeof(*errmsg)"? So if it's > >0, we need to append the nlh contents. I was trying to avoid using payload in case it has overflown :S > > + void *data; > > + > > + data = nlmsg_append(skb, rep, data_len); > > + if (!data) > > + goto err_bad_put; > > + > > + /* the nlh + 1 is probably going to make you > > unhappy? */ > > Right, the compiler may think it is an object no larger than > sizeof(*nlh). My earliest attempt at changes here introduced a > flex-array for the contents, and split the memcpy: > https://lore.kernel.org/lkml/d7251d92-150b-5346-6237-52afc154bb00@rasmusvillemoes.dk/ > which is basically the solution you have here, except it wasn't having > the nlmsg_*-helpers do the bounds checking. > > > + memcpy(data, nlh + 1, data_len); > > So with the struct nlmsghdr::nlmsg_contents member, this becomes: > > memcpy(data, nlh->nlmsg_contents, data_len); >
Powered by blists - more mailing lists