Add read and write support to tls_buffer.

tls_buffer was original created for a specific use case, namely reading in
length prefixed messages. This adds read and write support, along with a
capacity limit, allowing it to be used in additional use cases.

ok beck@ tb@

1 files changed, 126 insertions, 7 deletions

diff --git a/lib/libssl/tls_buffer.c b/lib/libssl/tls_buffer.c
index 9bb6b62e511..f70cfbc1a0d 100644
--- a/lib/libssl/tls_buffer.c
+++ b/lib/libssl/tls_buffer.c
@@ -1,6 +1,6 @@
-/* $OpenBSD: tls_buffer.c,v 1.2 2022/07/20 06:32:24 jsing Exp $ */
+/* $OpenBSD: tls_buffer.c,v 1.3 2022/07/22 19:33:53 jsing Exp $ */
 /*
- * Copyright (c) 2018, 2019 Joel Sing <jsing@openbsd.org>
+ * Copyright (c) 2018, 2019, 2022 Joel Sing <jsing@openbsd.org>
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -21,8 +21,11 @@
 #include "bytestring.h"
 #include "tls_internal.h"
 
+#define TLS_BUFFER_CAPACITY_LIMIT	(1024 * 1024)
+
 struct tls_buffer {
 	size_t capacity;
+	size_t capacity_limit;
 	uint8_t *data;
 	size_t len;
 	size_t offset;
@@ -38,6 +41,8 @@ tls_buffer_new(size_t init_size)
 	if ((buf = calloc(1, sizeof(struct tls_buffer))) == NULL)
 		goto err;
 
+	buf->capacity_limit = TLS_BUFFER_CAPACITY_LIMIT;
+
 	if (!tls_buffer_resize(buf, init_size))
 		goto err;
 
@@ -50,32 +55,76 @@ tls_buffer_new(size_t init_size)
 }
 
 void
+tls_buffer_clear(struct tls_buffer *buf)
+{
+	freezero(buf->data, buf->capacity);
+
+	buf->data = NULL;
+	buf->capacity = 0;
+	buf->len = 0;
+	buf->offset = 0;
+}
+
+void
 tls_buffer_free(struct tls_buffer *buf)
 {
 	if (buf == NULL)
 		return;
 
-	freezero(buf->data, buf->capacity);
+	tls_buffer_clear(buf);
+
 	freezero(buf, sizeof(struct tls_buffer));
 }
 
 static int
+tls_buffer_grow(struct tls_buffer *buf, size_t capacity)
+{
+	if (buf->capacity >= capacity)
+		return 1;
+
+	return tls_buffer_resize(buf, capacity);
+}
+
+static int
 tls_buffer_resize(struct tls_buffer *buf, size_t capacity)
 {
 	uint8_t *data;
 
+	/*
+	 * XXX - Consider maintaining a minimum size and growing more
+	 * intelligently (rather than exactly).
+	 */
 	if (buf->capacity == capacity)
 		return 1;
 
+	if (capacity > buf->capacity_limit)
+		return 0;
+
 	if ((data = recallocarray(buf->data, buf->capacity, capacity, 1)) == NULL)
 		return 0;
 
 	buf->data = data;
 	buf->capacity = capacity;
 
+	/* Ensure that len and offset are valid if capacity decreased. */
+	if (buf->len > buf->capacity)
+		buf->len = buf->capacity;
+	if (buf->offset > buf->len)
+		buf->offset = buf->len;
+
 	return 1;
 }
 
+void
+tls_buffer_set_capacity_limit(struct tls_buffer *buf, size_t limit)
+{
+	/*
+	 * XXX - do we want to force a resize if this limit is less than current
+	 * capacity... and what do we do with existing data? Force a clear?
+	 */
+	buf->capacity_limit = limit;
+}
+
 ssize_t
 tls_buffer_extend(struct tls_buffer *buf, size_t len,
     tls_read_cb read_cb, void *cb_arg)
@@ -106,10 +155,79 @@ tls_buffer_extend(struct tls_buffer *buf, size_t len,
 	}
 }
 
-void
-tls_buffer_cbs(struct tls_buffer *buf, CBS *cbs)
+ssize_t
+tls_buffer_read(struct tls_buffer *buf, uint8_t *rbuf, size_t n)
+{
+	if (buf->offset > buf->len)
+		return TLS_IO_FAILURE;
+
+	if (buf->offset == buf->len)
+		return TLS_IO_WANT_POLLIN;
+
+	if (n > buf->len - buf->offset)
+		n = buf->len - buf->offset;
+
+	memcpy(rbuf, &buf->data[buf->offset], n);
+
+	buf->offset += n;
+
+	return n;
+}
+
+ssize_t
+tls_buffer_write(struct tls_buffer *buf, const uint8_t *wbuf, size_t n)
+{
+	if (buf->offset > buf->len)
+		return TLS_IO_FAILURE;
+
+	/*
+	 * To avoid continually growing the buffer, pull data up to the
+	 * start of the buffer. If all data has been read then we can simply
+	 * reset, otherwise wait until we're going to save at least 4KB of
+	 * memory to reduce overhead.
+	 */
+	if (buf->offset == buf->len) {
+		buf->len = 0;
+		buf->offset = 0;
+	}
+	if (buf->offset >= 4096) {
+		memmove(buf->data, &buf->data[buf->offset],
+		    buf->len - buf->offset);
+		buf->len -= buf->offset;
+		buf->offset = 0;
+	}
+
+	if (buf->len > SIZE_MAX - n)
+		return TLS_IO_FAILURE;
+	if (!tls_buffer_grow(buf, buf->len + n))
+		return TLS_IO_FAILURE;
+
+	memcpy(&buf->data[buf->len], wbuf, n);
+
+	buf->len += n;
+
+	return n;
+}
+
+int
+tls_buffer_append(struct tls_buffer *buf, const uint8_t *wbuf, size_t n)
+{
+	return tls_buffer_write(buf, wbuf, n) == n;
+}
+
+int
+tls_buffer_data(struct tls_buffer *buf, CBS *out_cbs)
 {
-	CBS_init(cbs, buf->data, buf->len);
+	CBS cbs;
+
+	CBS_init(&cbs, buf->data, buf->len);
+
+	if (!CBS_skip(&cbs, buf->offset))
+		return 0;
+
+	CBS_dup(&cbs, out_cbs);
+
+	return 1;
 }
 
 int
@@ -121,9 +239,10 @@ tls_buffer_finish(struct tls_buffer *buf, uint8_t **out, size_t *out_len)
 	*out = buf->data;
 	*out_len = buf->len;
 
-	buf->capacity = 0;
 	buf->data = NULL;
+	buf->capacity = 0;
 	buf->len = 0;
+	buf->offset = 0;
 
 	return 1;
 }