Author: jhb
Date: Tue Oct 13 17:30:34 2020
New Revision: 366674
URL: https://svnweb.freebsd.org/changeset/base/366674
Log:
Permit sending empty fragments for TLS 1.0.
Due to a weakness in the TLS 1.0 protocol, OpenSSL will periodically
send empty TLS records ("empty fragments"). These TLS records have no
payload (and thus a page count of zero). m_uiotombuf_nomap() was
returning NULL instead of an empty mbuf, and a few places needed to be
updated to treat an empty TLS record as having a page count of "1" as
0 means "no work to do" (e.g. nothing to encrypt, or nothing to mark
ready via sbready()).
Reviewed by: gallatin
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D26729
Modified:
head/sys/kern/uipc_ktls.c
head/sys/kern/uipc_mbuf.c
head/sys/kern/uipc_sockbuf.c
Modified: head/sys/kern/uipc_ktls.c
==============================================================================
--- head/sys/kern/uipc_ktls.c Tue Oct 13 17:27:37 2020 (r366673)
+++ head/sys/kern/uipc_ktls.c Tue Oct 13 17:30:34 2020 (r366674)
@@ -1384,7 +1384,9 @@ ktls_seq(struct sockbuf *sb, struct mbuf *m)
* The enq_count argument on return is set to the number of pages of
* payload data for this entire chain that need to be encrypted via SW
* encryption. The returned value should be passed to ktls_enqueue
- * when scheduling encryption of this chain of mbufs.
+ * when scheduling encryption of this chain of mbufs. To handle the
+ * special case of empty fragments for TLS 1.0 sessions, an empty
+ * fragment counts as one page.
*/
void
ktls_frame(struct mbuf *top, struct ktls_session *tls, int *enq_cnt,
@@ -1400,12 +1402,16 @@ ktls_frame(struct mbuf *top, struct ktls_session *tls,
*enq_cnt = 0;
for (m = top; m != NULL; m = m->m_next) {
/*
- * All mbufs in the chain should be non-empty TLS
- * records whose payload does not exceed the maximum
- * frame length.
+ * 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.
*/
- KASSERT(m->m_len <= maxlen && m->m_len > 0,
+ 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));
+
/*
* TLS frames require unmapped mbufs to store session
* info.
@@ -1496,7 +1502,11 @@ ktls_frame(struct mbuf *top, struct ktls_session *tls,
if (tls->mode == TCP_TLS_MODE_SW) {
m->m_flags |= M_NOTREADY;
m->m_epg_nrdy = m->m_epg_npgs;
- *enq_cnt += m->m_epg_npgs;
+ if (__predict_false(tls_len == 0)) {
+ /* TLS 1.0 empty fragment. */
+ *enq_cnt += 1;
+ } else
+ *enq_cnt += m->m_epg_npgs;
}
}
}
@@ -1961,7 +1971,11 @@ retry_page:
dst_iov[i].iov_len = len;
}
- npages += i;
+ if (__predict_false(m->m_epg_npgs == 0)) {
+ /* TLS 1.0 empty fragment. */
+ npages++;
+ } else
+ npages += i;
error = (*tls->sw_encrypt)(tls,
(const struct tls_record_layer *)m->m_epg_hdr,
Modified: head/sys/kern/uipc_mbuf.c
==============================================================================
--- head/sys/kern/uipc_mbuf.c Tue Oct 13 17:27:37 2020 (r366673)
+++ head/sys/kern/uipc_mbuf.c Tue Oct 13 17:30:34 2020 (r366674)
@@ -1655,6 +1655,8 @@ m_uiotombuf_nomap(struct uio *uio, int how, int len, i
int pflags = malloc2vm_flags(how) | VM_ALLOC_NOOBJ | VM_ALLOC_NODUMP |
VM_ALLOC_WIRED;
+ MPASS((flags & M_PKTHDR) == 0);
+
/*
* len can be zero or an arbitrary large value bound by
* the total data supplied by the uio.
@@ -1668,10 +1670,23 @@ m_uiotombuf_nomap(struct uio *uio, int how, int len, i
maxseg = MBUF_PEXT_MAX_PGS * PAGE_SIZE;
/*
+ * If total is zero, return an empty mbuf. This can occur
+ * for TLS 1.0 connections which send empty fragments as
+ * a countermeasure against the known-IV weakness in CBC
+ * ciphersuites.
+ */
+ if (__predict_false(total == 0)) {
+ mb = mb_alloc_ext_pgs(how, mb_free_mext_pgs);
+ if (mb == NULL)
+ return (NULL);
+ mb->m_epg_flags = EPG_FLAG_ANON;
+ return (mb);
+ }
+
+ /*
* Allocate the pages
*/
m = NULL;
- MPASS((flags & M_PKTHDR) == 0);
while (total > 0) {
mb = mb_alloc_ext_pgs(how, mb_free_mext_pgs);
if (mb == NULL)
Modified: head/sys/kern/uipc_sockbuf.c
==============================================================================
--- head/sys/kern/uipc_sockbuf.c Tue Oct 13 17:27:37 2020
(r366673)
+++ head/sys/kern/uipc_sockbuf.c Tue Oct 13 17:30:34 2020
(r366674)
@@ -212,7 +212,7 @@ sbready(struct sockbuf *sb, struct mbuf *m0, int count
while (count > 0) {
KASSERT(m->m_flags & M_NOTREADY,
("%s: m %p !M_NOTREADY", __func__, m));
- if ((m->m_flags & M_EXTPG) != 0) {
+ if ((m->m_flags & M_EXTPG) != 0 && m->m_epg_npgs != 0) {
if (count < m->m_epg_nrdy) {
m->m_epg_nrdy -= count;
count = 0;
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