Wrap some tvb_get_ptr calls in crc32c_tvb_offset_calculate().

This eliminates some tvb_get_ptr calls from dissectors, as part of
trying to minimize if not eliminate its use in dissectors (it's a bit of
what's called an "attractive nuisance", in that users who don't
understand what it does - and doesn't! - do may use it in ways that are
unsafe, e.g. thinking you can use it to get a null-terminated string
from a packet).

It also eliminates the possibility of passing one length to
tvb_get_ptr() and another to crc32c_calculate().

Change-Id: I8a07168d0bc088b45d607e00c5bb1d98421ebc73
Reviewed-on: https://code.wireshark.org/review/3488
Reviewed-by: Guy Harris <guy@alum.mit.edu>

1 files changed, 11 insertions, 0 deletions

diff --git a/epan/crc32-tvb.c b/epan/crc32-tvb.c
index 68b4d119cb..e729ce79cf 100644
--- a/epan/crc32-tvb.c
+++ b/epan/crc32-tvb.c
@@ -78,6 +78,17 @@ crc32_ccitt_tvb_offset_seed(tvbuff_t *tvb, guint offset, guint len,
 	return ( crc32_ccitt_seed(buf, len, seed) );
 }
 
+guint32
+crc32c_tvb_offset_calculate(tvbuff_t *tvb, guint offset, guint len, guint32 seed)
+{
+	const guint8* buf;
+
+	tvb_ensure_bytes_exist(tvb, offset, len);  /* len == -1 not allowed */
+	buf = tvb_get_ptr(tvb, offset, len);
+
+	return ( crc32c_calculate(buf, len, seed) );
+}
+
 /*
  * IEEE 802.x version (Ethernet and 802.11, at least) - byte-swap
  * the result of "crc32()".