linux-kernel - Re: [PATCH net] tls: fix NULL deref on tls_sw_splice

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Message-ID: <CAG48ez3dn7CAfTmfziBUd_aFfcM1LOYsUuYrKykZAvTv=AAodg@mail.gmail.com>
Date:   Wed, 22 Nov 2023 22:58:13 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Boris Pismenny <borisp@...dia.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Cc:     David Howells <dhowells@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] tls: fix NULL deref on tls_sw_splice_eof() with empty record

On Wed, Nov 22, 2023 at 10:44 PM Jann Horn <jannh@...gle.com> wrote:
> syzkaller discovered that if tls_sw_splice_eof() is executed as part of
> sendfile() when the plaintext/ciphertext sk_msg are empty, the send path
> gets confused because the empty ciphertext buffer does not have enough
> space for the encryption overhead. This causes tls_push_record() to go on
> the `split = true` path (which is only supposed to be used when interacting
> with an attached BPF program), and then get further confused and hit the
> tls_merge_open_record() path, which then assumes that there must be at
> least one populated buffer element, leading to a NULL deref.

Ah, and in case you're looking for the corresponding syzkaller report,
you can find that at
<https://lore.kernel.org/all/000000000000347a250608e8a4d1@google.com/T/>.