Messages in this thread | | | Date | Wed, 31 Aug 2022 23:27:08 -0700 | From | Kees Cook <> | Subject | Re: [PATCH 1/2] netlink: Bounds-check nlmsg_len() |
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On Wed, Aug 31, 2022 at 08:18:25PM -0700, Jakub Kicinski wrote: > On Wed, 31 Aug 2022 20:06:09 -0700 Kees Cook wrote: > > static inline int nlmsg_len(const struct nlmsghdr *nlh) > > { > > - return nlh->nlmsg_len - NLMSG_HDRLEN; > > + u32 nlmsg_contents_len; > > + > > + if (WARN_ON_ONCE(check_sub_overflow(nlh->nlmsg_len, > > + (u32)NLMSG_HDRLEN, > > + &nlmsg_contents_len))) > > + return 0; > > + if (WARN_ON_ONCE(nlmsg_contents_len > INT_MAX)) > > + return INT_MAX; > > + return nlmsg_contents_len; > > We check the messages on input, making sure the length is valid wrt > skb->len, and sane, ie > NLMSG_HDRLEN. See netlink_rcv_skb(). > > Can we not, pretty please? :(
This would catch corrupted values...
Is the concern the growth in image size? The check_sub_overflow() isn't large at all -- it's just adding a single overflow bit test. The WARNs are heavier, but they're all out-of-line.
-- Kees Cook
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