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    SubjectRe: [PATCH v2] netfilter: nfnetlink: Improve input length sanitization in nfnetlink_rcv
    On Thu, Jun 29, 2017 at 6:22 PM, Pablo Neira Ayuso <pablo@netfilter.org> wrote:
    > On Tue, Jun 27, 2017 at 07:05:27PM +0200, Pablo Neira Ayuso wrote:
    >> On Tue, Jun 27, 2017 at 05:58:25PM +0200, Pablo Neira Ayuso wrote:
    >> > On Wed, Jun 07, 2017 at 03:50:38PM +0200, Mateusz Jurczyk wrote:
    >> > > Verify that the length of the socket buffer is sufficient to cover the
    >> > > nlmsghdr structure before accessing the nlh->nlmsg_len field for further
    >> > > input sanitization. If the client only supplies 1-3 bytes of data in
    >> > > sk_buff, then nlh->nlmsg_len remains partially uninitialized and
    >> > > contains leftover memory from the corresponding kernel allocation.
    >> > > Operating on such data may result in indeterminate evaluation of the
    >> > > nlmsg_len < NLMSG_HDRLEN expression.
    >> > >
    >> > > The bug was discovered by a runtime instrumentation designed to detect
    >> > > use of uninitialized memory in the kernel. The patch prevents this and
    >> > > other similar tools (e.g. KMSAN) from flagging this behavior in the future.
    >> >
    >> > Applied, thanks.
    >>
    >> Wait, I keeping this back after closer look.
    >>
    >> I think we have to remove this:
    >>
    >> if (nlh->nlmsg_len < NLMSG_HDRLEN || <---
    >> skb->len < NLMSG_HDRLEN + sizeof(struct nfgenmsg))
    >> return;
    >>
    >> in nfnetlink_rcv_skb_batch()
    >>
    >> now that we make this unfront check from nfnetlink_rcv().
    >
    > BTW, I can just mangle your patch here to delete such line to speed up
    > things. See the mangled patch that is attached to this email.

    Sure, I think the condition in nfnetlink_rcv_skb_batch() can be now
    safely removed. Feel free to proceed with the mangled patch. Thanks.

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