CVE-2023-52767

In the Linux kernel, the following vulnerability has been resolved: tls:
fix NULL deref on tls_sw_splice_eof() with empty record 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. It is possible
to have empty plaintext/ciphertext buffers if we previously bailed from
tls_sw_sendmsg_locked() via the tls_trim_both_msgs() path.
tls_sw_push_pending_record() already handles this case correctly; let’s do
the same check in tls_sw_splice_eof().