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ktls: Disallow transmitting empty frames outside of TLS 1.0/CBC mode

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There was nothing preventing one from sending an empty fragment on an
arbitrary KTLS TX-enabled socket, but ktls_frame() asserts that this
could not happen.  Though the transmit path handles this case for TLS
1.0 with AES-CBC, we should be strict and allow empty fragments only in
modes where it is explicitly allowed.

Modify sosend_generic() to reject writes to a KTLS-enabled socket if the
number of data bytes is zero, so that userspace cannot trigger the
aforementioned assertion.

Add regression tests to exercise this case.

Reported by:	syzkaller
Reviewed by:	gallatin, jhb
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D34195
This commit is contained in:
Mark Johnston 2022-02-08 12:36:41 -05:00
parent 300cfb96fc
commit 5de79eeddb
4 changed files with 41 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
sys/kern/uipc_ktls.c
View File

@ -1691,19 +1691,18 @@ ktls_frame(struct mbuf *top, struct ktls_session *tls, int *enq_cnt,
* All mbufs in the chain should be TLS records whose
* payload does not exceed the maximum frame length.
*
* Empty TLS records are permitted when using CBC.
* Empty TLS 1.0 records are permitted when using CBC.
*/
KASSERT(m->m_len <= maxlen &&
(tls->params.cipher_algorithm == CRYPTO_AES_CBC ?
m->m_len >= 0 : m->m_len > 0),
("ktls_frame: m %p len %d\n", m, m->m_len));
KASSERT(m->m_len <= maxlen && m->m_len >= 0 &&
(m->m_len > 0 || ktls_permit_empty_frames(tls)),
("ktls_frame: m %p len %d", m, m->m_len));
/*
* TLS frames require unmapped mbufs to store session
* info.
*/
KASSERT((m->m_flags & M_EXTPG) != 0,
("ktls_frame: mapped mbuf %p (top = %p)\n", m, top));
("ktls_frame: mapped mbuf %p (top = %p)", m, top));
tls_len = m->m_len;
@ -1797,6 +1796,13 @@ ktls_frame(struct mbuf *top, struct ktls_session *tls, int *enq_cnt,
}
}
bool
ktls_permit_empty_frames(struct ktls_session *tls)
{
return (tls->params.cipher_algorithm == CRYPTO_AES_CBC &&
tls->params.tls_vminor == TLS_MINOR_VER_ZERO);
}
void
ktls_check_rx(struct sockbuf *sb)
{

5
sys/kern/uipc_socket.c
View File

@ -1667,6 +1667,11 @@ sosend_generic(struct socket *so, struct sockaddr *addr, struct uio *uio,
atomic = 1;
}
}
if (resid == 0 && !ktls_permit_empty_frames(tls)) {
error = EINVAL;
goto release;
}
}
#endif

1
sys/sys/ktls.h
View File

@ -213,6 +213,7 @@ int ktls_enable_tx(struct socket *so, struct tls_enable *en);
void ktls_destroy(struct ktls_session *tls);
void ktls_frame(struct mbuf *m, struct ktls_session *tls, int *enqueue_cnt,
uint8_t record_type);
bool ktls_permit_empty_frames(struct ktls_session *tls);
void ktls_seq(struct sockbuf *sb, struct mbuf *m);
void ktls_enqueue(struct mbuf *m, struct socket *so, int page_count);
void ktls_enqueue_to_free(struct mbuf *m);

31
tests/sys/kern/ktls_test.c
View File

@ -1105,9 +1105,19 @@ test_ktls_transmit_empty_fragment(struct tls_enable *en, uint64_t seqno)
fd_set_blocking(sockets[0]);
fd_set_blocking(sockets[1]);
/* A write of zero bytes should send an empty fragment. */
/*
* A write of zero bytes should send an empty fragment only for
* TLS 1.0, otherwise an error should be raised.
*/
rv = write(sockets[1], NULL, 0);
ATF_REQUIRE(rv == 0);
if (rv == 0) {
ATF_REQUIRE(en->cipher_algorithm == CRYPTO_AES_CBC);
ATF_REQUIRE(en->tls_vminor == TLS_MINOR_VER_ZERO);
} else {
ATF_REQUIRE(rv == -1);
ATF_REQUIRE(errno == EINVAL);
goto out;
}
/*
* First read the header to determine how much additional data
@ -1129,6 +1139,7 @@ test_ktls_transmit_empty_fragment(struct tls_enable *en, uint64_t seqno)
"read %zd decrypted bytes for an empty fragment", rv);
ATF_REQUIRE(record_type == TLS_RLTYPE_APP);
out:
free(outbuf);
ATF_REQUIRE(close(sockets[1]) == 0);
@ -1369,7 +1380,7 @@ ATF_TC_BODY(ktls_transmit_##cipher_name##_##name, tc) \
ATF_TP_ADD_TC(tp, ktls_transmit_##cipher_name##_##name);
#define GEN_TRANSMIT_EMPTY_FRAGMENT_TEST(cipher_name, cipher_alg, \
key_size, auth_alg) \
key_size, auth_alg, minor) \
ATF_TC_WITHOUT_HEAD(ktls_transmit_##cipher_name##_empty_fragment); \
ATF_TC_BODY(ktls_transmit_##cipher_name##_empty_fragment, tc) \
{ \
@ -1378,14 +1389,14 @@ ATF_TC_BODY(ktls_transmit_##cipher_name##_empty_fragment, tc) \
\
ATF_REQUIRE_KTLS(); \
seqno = random(); \
build_tls_enable(cipher_alg, key_size, auth_alg, \
TLS_MINOR_VER_ZERO, seqno, &en); \
build_tls_enable(cipher_alg, key_size, auth_alg, minor, seqno, \
&en); \
test_ktls_transmit_empty_fragment(&en, seqno); \
free_tls_enable(&en); \
}
#define ADD_TRANSMIT_EMPTY_FRAGMENT_TEST(cipher_name, cipher_alg, \
key_size, auth_alg) \
key_size, auth_alg, minor) \
ATF_TP_ADD_TC(tp, ktls_transmit_##cipher_name##_empty_fragment);
#define GEN_TRANSMIT_TESTS(cipher_name, cipher_alg, key_size, auth_alg, \
@ -1506,7 +1517,9 @@ AES_CBC_TESTS(GEN_TRANSMIT_PADDING_TESTS);
* Test "empty fragments" which are TLS records with no payload that
* OpenSSL can send for TLS 1.0 connections.
*/
TLS_10_TESTS(GEN_TRANSMIT_EMPTY_FRAGMENT_TEST);
AES_CBC_TESTS(GEN_TRANSMIT_EMPTY_FRAGMENT_TEST);
AES_GCM_TESTS(GEN_TRANSMIT_EMPTY_FRAGMENT_TEST);
CHACHA20_TESTS(GEN_TRANSMIT_EMPTY_FRAGMENT_TEST);
static void
test_ktls_invalid_transmit_cipher_suite(struct tls_enable *en)
@ -1768,7 +1781,9 @@ ATF_TP_ADD_TCS(tp)
AES_GCM_TESTS(ADD_TRANSMIT_TESTS);
CHACHA20_TESTS(ADD_TRANSMIT_TESTS);
AES_CBC_TESTS(ADD_TRANSMIT_PADDING_TESTS);
TLS_10_TESTS(ADD_TRANSMIT_EMPTY_FRAGMENT_TEST);
AES_CBC_TESTS(ADD_TRANSMIT_EMPTY_FRAGMENT_TEST);
AES_GCM_TESTS(ADD_TRANSMIT_EMPTY_FRAGMENT_TEST);
CHACHA20_TESTS(ADD_TRANSMIT_EMPTY_FRAGMENT_TEST);
INVALID_CIPHER_SUITES(ADD_INVALID_TRANSMIT_TEST);
/* Receive tests */