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tls: fix NULL deref on tls_sw_splice_eof() with empty record

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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().

Fixes: df720d288d ("tls/sw: Use splice_eof() to flush")
Cc: stable@vger.kernel.org
Reported-by: syzbot+40d43509a099ea756317@syzkaller.appspotmail.com
Signed-off-by: Jann Horn <jannh@google.com>
Link: https://lore.kernel.org/r/20231122214447.675768-1-jannh@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jann Horn 2023-11-22 22:44:47 +01:00 committed by Jakub Kicinski
parent fd0413bbf8
commit 53f2cb491b
1 changed files with 3 additions and 0 deletions
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3
net/tls/tls_sw.c
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@ -1232,11 +1232,14 @@ void tls_sw_splice_eof(struct socket *sock)
lock_sock(sk);
retry:
/* same checks as in tls_sw_push_pending_record() */
rec = ctx->open_rec;
if (!rec)
goto unlock;
msg_pl = &rec->msg_plaintext;
if (msg_pl->sg.size == 0)
goto unlock;
/* Check the BPF advisor and perform transmission. */
ret = bpf_exec_tx_verdict(msg_pl, sk, false, TLS_RECORD_TYPE_DATA,