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nhrp: clean up extension parsing. 

For the top-level item for an extension, initially create it with a
length of "to the end of the packet" and, when we finish dissecting it,
set the length appropriately.  That way, if the length is too large, we
don't throw an immediate exception, making it a little clearer what's
happending.

When dissecting an authentication extension, construct the text of the
top-level item as we dissect it, and initially create it with a length
of "to the end of the packet" and, when we're finished dissecting it,
set the length appropriately.  That way, we don't throw an exception
before doing any dissection if the data for the item isn't all there, we
only throw an exception when we run out of data, and we also don't try
to add the data unless there is at least one byte of data.

The latter of those fixes #18181.
This commit is contained in:
Guy Harris 2022-07-07 02:03:26 -07:00
parent f296a00f09
commit abe8798b78
1 changed files with 13 additions and 6 deletions
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19
epan/dissectors/packet-nhrp.c
View File

@ -814,6 +814,7 @@ static void dissect_nhrp_ext(tvbuff_t *tvb,
while ((offset + 4) <= extEnd)
{
proto_tree *nhrp_tree;
proto_item *nhrp_item;
gint extTypeC = tvb_get_ntohs(tvb, offset);
gint extType = extTypeC & 0x3FFF;
guint len = tvb_get_ntohs(tvb, offset+2);
@ -822,11 +823,11 @@ static void dissect_nhrp_ext(tvbuff_t *tvb,
/* Assume it's not really a Cisco NAT extension, but a device
* capabilities extension instead (see RFC 2735). */
nhrp_tree = proto_tree_add_subtree(tree, tvb, offset,
len + 4, ett_nhrp_ext, NULL, "Device Capabilities Extension");
-1, ett_nhrp_ext, &nhrp_item, "Device Capabilities Extension");
}
else {
nhrp_tree = proto_tree_add_subtree(tree, tvb, offset,
len + 4, ett_nhrp_ext, NULL,
-1, ett_nhrp_ext, &nhrp_item,
val_to_str(extType, ext_type_vals, "Unknown (%u)"));
}
proto_tree_add_boolean(nhrp_tree, hf_nhrp_ext_C, tvb, offset, 2, extTypeC);
@ -881,12 +882,14 @@ static void dissect_nhrp_ext(tvbuff_t *tvb,
}
else {
proto_tree *auth_tree;
proto_item *auth_item;
guint32 spi;
auth_tree = proto_tree_add_subtree_format(nhrp_tree, tvb, offset, len,
ett_nhrp_auth_ext, NULL, "Extension Data: SPI=%u: Data=%s", tvb_get_ntohs(tvb, offset + 2),
tvb_bytes_to_str(pinfo->pool, tvb, offset + 4 + srcLen, len - (4 + srcLen)));
auth_tree = proto_tree_add_subtree_format(nhrp_tree, tvb, offset, -1,
ett_nhrp_auth_ext, &auth_item, "Extension Data");
proto_tree_add_item(auth_tree, hf_nhrp_auth_ext_reserved, tvb, offset, 2, ENC_BIG_ENDIAN);
proto_tree_add_item(auth_tree, hf_nhrp_auth_ext_spi, tvb, offset + 2, 2, ENC_BIG_ENDIAN);
proto_tree_add_item_ret_uint(auth_tree, hf_nhrp_auth_ext_spi, tvb, offset + 2, 2, ENC_BIG_ENDIAN, &spi);
proto_item_append_text(auth_item, ": SPI=%u", spi);
if (srcLen == 4)
proto_tree_add_item(auth_tree, hf_nhrp_auth_ext_src_addr, tvb, offset + 4, 4, ENC_BIG_ENDIAN);
else if (srcLen) {
@ -894,7 +897,10 @@ static void dissect_nhrp_ext(tvbuff_t *tvb,
}
if (len > (4 + srcLen)) {
proto_tree_add_item(auth_tree, hf_nhrp_auth_data, tvb, offset + 4 + srcLen, len - (4 + srcLen), ENC_NA);
proto_item_append_text(auth_item, ": Data=%s",
tvb_bytes_to_str(pinfo->pool, tvb, offset + 4 + srcLen, len - (4 + srcLen)));
}
proto_item_set_len(auth_item, len);
}
break;
@ -935,6 +941,7 @@ static void dissect_nhrp_ext(tvbuff_t *tvb,
skip_switch:
offset += len;
}
proto_item_set_end(nhrp_item, tvb, offset);
if (!nested) {
len = tvb_reported_length_remaining(tvb, offset);