Re: [PATCH net] tls: fix NULL deref on tls_sw_splice_eof() with empty record

[Jann Horn]

On Wed, Nov 22, 2023 at 10:44 PM Jann Horn <jannh@xxxxxxxxxx> 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@xxxxxxxxxx/T/>.