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

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Date:   Sun, 26 Nov 2023 15:56:46 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     Jann Horn <jannh@...gle.com>, 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

Jann Horn wrote:
> 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/>.

I'm a bit slow, but looks good to me as well. Thanks a lot.

Acked-by: John Fastabend <john.fastabend@...il.com>