From 3f6877b440d5d44fc0c6d366d1b5d5fdeead626c Mon Sep 17 00:00:00 2001
From: jsing <>
Date: Wed, 15 Dec 2021 17:36:49 +0000
Subject: Provide various CBS_peek_* functions.
These will be used in libcrypto.
With input from and ok tb@
---
src/lib/libssl/bs_cbs.c | 79 ++++++++++++++++++++++++++++++++++++++++++++-
src/lib/libssl/bytestring.h | 32 +++++++++++++++++-
2 files changed, 109 insertions(+), 2 deletions(-)
diff --git a/src/lib/libssl/bs_cbs.c b/src/lib/libssl/bs_cbs.c
index 97b0163f3f..63c078c9b0 100644
--- a/src/lib/libssl/bs_cbs.c
+++ b/src/lib/libssl/bs_cbs.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: bs_cbs.c,v 1.23 2021/12/15 17:30:20 jsing Exp $ */
+/* $OpenBSD: bs_cbs.c,v 1.24 2021/12/15 17:36:49 jsing Exp $ */
/*
* Copyright (c) 2014, Google Inc.
*
@@ -47,6 +47,16 @@ cbs_get(CBS *cbs, const uint8_t **p, size_t n)
return 1;
}
+static int
+cbs_peek(CBS *cbs, const uint8_t **p, size_t n)
+{
+ if (cbs->len < n)
+ return 0;
+
+ *p = cbs->data;
+ return 1;
+}
+
size_t
CBS_offset(const CBS *cbs)
{
@@ -259,6 +269,73 @@ CBS_get_u24_length_prefixed(CBS *cbs, CBS *out)
return cbs_get_length_prefixed(cbs, out, 3);
}
+static int
+cbs_peek_u(CBS *cbs, uint32_t *out, size_t len)
+{
+ uint32_t result = 0;
+ size_t i;
+ const uint8_t *data;
+
+ if (len < 1 || len > 4)
+ return 0;
+
+ if (!cbs_peek(cbs, &data, len))
+ return 0;
+
+ for (i = 0; i < len; i++) {
+ result <<= 8;
+ result |= data[i];
+ }
+ *out = result;
+ return 1;
+}
+
+int
+CBS_peek_u8(CBS *cbs, uint8_t *out)
+{
+ const uint8_t *v;
+
+ if (!cbs_peek(cbs, &v, 1))
+ return 0;
+
+ *out = *v;
+ return 1;
+}
+
+int
+CBS_peek_u16(CBS *cbs, uint16_t *out)
+{
+ uint32_t v;
+
+ if (!cbs_peek_u(cbs, &v, 2))
+ return 0;
+
+ *out = v;
+ return 1;
+}
+
+int
+CBS_peek_u24(CBS *cbs, uint32_t *out)
+{
+ return cbs_peek_u(cbs, out, 3);
+}
+
+int
+CBS_peek_u32(CBS *cbs, uint32_t *out)
+{
+ return cbs_peek_u(cbs, out, 4);
+}
+
+int
+CBS_peek_last_u8(CBS *cbs, uint8_t *out)
+{
+ if (cbs->len == 0)
+ return 0;
+
+ *out = cbs->data[cbs->len - 1];
+ return 1;
+}
+
int
CBS_get_any_asn1_element(CBS *cbs, CBS *out, unsigned int *out_tag,
size_t *out_header_len)
diff --git a/src/lib/libssl/bytestring.h b/src/lib/libssl/bytestring.h
index fa5e05fa27..ce933f3f7b 100644
--- a/src/lib/libssl/bytestring.h
+++ b/src/lib/libssl/bytestring.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: bytestring.h,v 1.21 2021/12/15 17:30:20 jsing Exp $ */
+/* $OpenBSD: bytestring.h,v 1.22 2021/12/15 17:36:49 jsing Exp $ */
/*
* Copyright (c) 2014, Google Inc.
*
@@ -172,6 +172,36 @@ int CBS_get_u16_length_prefixed(CBS *cbs, CBS *out);
*/
int CBS_get_u24_length_prefixed(CBS *cbs, CBS *out);
+/*
+ * CBS_peek_u8 sets |*out| to the next uint8_t from |cbs|, but does not advance
+ * |cbs|. It returns one on success and zero on error.
+ */
+int CBS_peek_u8(CBS *cbs, uint8_t *out);
+
+/*
+ * CBS_peek_u16 sets |*out| to the next, big-endian uint16_t from |cbs|, but
+ * does not advance |cbs|. It returns one on success and zero on error.
+ */
+int CBS_peek_u16(CBS *cbs, uint16_t *out);
+
+/*
+ * CBS_peek_u24 sets |*out| to the next, big-endian 24-bit value from |cbs|, but
+ * does not advance |cbs|. It returns one on success and zero on error.
+ */
+int CBS_peek_u24(CBS *cbs, uint32_t *out);
+
+/*
+ * CBS_peek_u32 sets |*out| to the next, big-endian uint32_t value from |cbs|,
+ * but does not advance |cbs|. It returns one on success and zero on error.
+ */
+int CBS_peek_u32(CBS *cbs, uint32_t *out);
+
+/*
+ * CBS_peek_last_u8 sets |*out| to the last uint8_t from |cbs|, but does not
+ * shorten |cbs|. It returns one on success and zero on error.
+ */
+int CBS_peek_last_u8(CBS *cbs, uint8_t *out);
+
/* Parsing ASN.1 */
--
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