opencrypto: Handle end-of-cursor conditions in crypto_cursor_segment()

Some consumers, e.g., swcr_encdec(), may call crypto_cursor_segment()
after having advanced the cursor to the end of the buffer.  In this case
I believe the right behaviour is to return NULL and a length of 0.

When this occurs with a CRYPTO_BUF_VMPAGE buffer, the cc_vmpage pointer
will point past the end of the page pointer array, so
crypto_cursor_segment() ends up dereferencing a random pointer before
the function returns a length of 0.  The uio-backed cursor has
a similar problem.

Address this by keeping track of the residual buffer length and
returning immediately once the length is zero.

PR:		271766
Reported by:	Andrew "RhodiumToad" Gierth <andrew@tao11.riddles.org.uk>
Reviewed by:	jhb
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D40428

1 files changed, 27 insertions, 7 deletions

diff --git a/sys/opencrypto/criov.c b/sys/opencrypto/criov.c
index 5312fe622c5e..c832a9af9eec 100644
--- a/sys/opencrypto/criov.c
+++ b/sys/opencrypto/criov.c
@@ -321,6 +321,7 @@ crypto_cursor_init(struct crypto_buffer_cursor *cc,
 		break;
 	case CRYPTO_BUF_UIO:
 		cc->cc_iov = cb->cb_uio->uio_iov;
+		cc->cc_buf_len = cb->cb_uio->uio_resid;
 		break;
 	default:
 #ifdef INVARIANTS
@@ -386,6 +387,7 @@ crypto_cursor_advance(struct crypto_buffer_cursor *cc, size_t amount)
 				cc->cc_offset += amount;
 				break;
 			}
+			cc->cc_buf_len -= remain;
 			amount -= remain;
 			cc->cc_iov++;
 			cc->cc_offset = 0;
@@ -406,14 +408,34 @@ crypto_cursor_segment(struct crypto_buffer_cursor *cc, size_t *len)
 {
 	switch (cc->cc_type) {
 	case CRYPTO_BUF_CONTIG:
-		*len = cc->cc_buf_len;
-		return (cc->cc_buf);
+	case CRYPTO_BUF_UIO:
+	case CRYPTO_BUF_VMPAGE:
+		if (cc->cc_buf_len == 0) {
+			*len = 0;
+			return (NULL);
+		}
+		break;
 	case CRYPTO_BUF_MBUF:
 	case CRYPTO_BUF_SINGLE_MBUF:
 		if (cc->cc_mbuf == NULL) {
 			*len = 0;
 			return (NULL);
 		}
+		break;
+	default:
+#ifdef INVARIANTS
+		panic("%s: invalid buffer type %d", __func__, cc->cc_type);
+#endif
+		*len = 0;
+		return (NULL);
+	}
+
+	switch (cc->cc_type) {
+	case CRYPTO_BUF_CONTIG:
+		*len = cc->cc_buf_len;
+		return (cc->cc_buf);
+	case CRYPTO_BUF_MBUF:
+	case CRYPTO_BUF_SINGLE_MBUF:
 		if (cc->cc_mbuf->m_flags & M_EXTPG)
 			return (m_epg_segment(cc->cc_mbuf, cc->cc_offset, len));
 		*len = cc->cc_mbuf->m_len - cc->cc_offset;
@@ -426,11 +448,7 @@ crypto_cursor_segment(struct crypto_buffer_cursor *cc, size_t *len)
 		*len = cc->cc_iov->iov_len - cc->cc_offset;
 		return ((char *)cc->cc_iov->iov_base + cc->cc_offset);
 	default:
-#ifdef INVARIANTS
-		panic("%s: invalid buffer type %d", __func__, cc->cc_type);
-#endif
-		*len = 0;
-		return (NULL);
+		__assert_unreachable();
 	}
 }
 
@@ -504,6 +522,7 @@ crypto_cursor_copyback(struct crypto_buffer_cursor *cc, int size,
 			todo = MIN(remain, size);
 			memcpy(dst, src, todo);
 			src += todo;
+			cc->cc_buf_len -= todo;
 			if (todo < remain) {
 				cc->cc_offset += todo;
 				break;
@@ -593,6 +612,7 @@ crypto_cursor_copydata(struct crypto_buffer_cursor *cc, int size, void *vdst)
 			todo = MIN(remain, size);
 			memcpy(dst, src, todo);
 			dst += todo;
+			cc->cc_buf_len -= todo;
 			if (todo < remain) {
 				cc->cc_offset += todo;
 				break;