netdev - RE: SO_PEERSEC protections in sk

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Date:   Mon, 10 Oct 2022 12:54:12 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Alexei Starovoitov' <alexei.starovoitov@...il.com>,
        Paul Moore <paul@...l-moore.com>
CC:     Martin KaFai Lau <martin.lau@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        "selinux@...r.kernel.org" <selinux@...r.kernel.org>
Subject: RE: SO_PEERSEC protections in sk_getsockopt()?

From: Alexei Starovoitov
> Sent: 07 October 2022 22:55
....
> Not easy at all.
> There is only way place in the whole kernel that does:
>                 return sk_getsockopt(sk, SOL_SOCKET, optname,
>                                      KERNEL_SOCKPTR(optval),
>                                      KERNEL_SOCKPTR(optlen));

Until I add change my out of tree driver to work with
the new code.
(Although it actually needs to do a getsockopt into SCTP.)

I didn't spot the change to sk_getsockopt() going though.
But KERNEL_SOCKPTR() is really the wrong function/type
for the length.
It would be much safer to have a struct with two members,
one an __user pointer and one a kernel pointer both to
socklen_t.

It isn't really ideal for the buffer pointer either.
That started as a single field (assuming the caller
has verified the user/kernel status), then the is_kernel
field was added for architectures where user/kernel
addresses use the same values.
Then a horrid bug (forgotten where) forced the is_kernel
field be used everywhere.
Again a structure with two pointers would be much safer.

Indeed the length could likely be included as well.
That would even give scope for a short user buffer being
copied into kernel memory while letting code that needs
a long buffer (or ignores the length) still directly
access userspace.

I can't remember, but something makes me think that a lot
of the 'not checking the length' setsockopt calls were in
decnet - which has now been deleted.

	David

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