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802.11: clean up data frame handling. 

Change

    case DATA_FRAME:
        if (condition) {
            do stuff;
            break;
        }
        do other stuff;
        break;

to

    case DATA_FRAME:
        if (condition) {
            do stuff;
        } else {
            do other stuff;
        }
        break;

to make it clearer that it's "do this if condition is true, else do
that".
This commit is contained in:
Guy Harris 2020-11-29 02:17:47 -08:00
parent ee764b8d7d
commit 258fb14821
1 changed files with 61 additions and 62 deletions
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123
epan/dissectors/packet-ieee80211.c
View File

@ -26754,79 +26754,78 @@ dissect_ieee80211_common(tvbuff_t *tvb, packet_info *pinfo,
call_dissector(llc_handle, msdu_tvb, pinfo, subframe_tree); call_dissector(llc_handle, msdu_tvb, pinfo, subframe_tree);
msdu_offset = roundup2(msdu_offset+msdu_length, 4); msdu_offset = roundup2(msdu_offset+msdu_length, 4);
} while (tvb_reported_length_remaining(next_tvb, msdu_offset) > 14); } while (tvb_reported_length_remaining(next_tvb, msdu_offset) > 14);
} else {
/* I guess some bridges take Netware Ethernet_802_3 frames,
which are 802.3 frames (with a length field rather than
a type field, but with no 802.2 header in the payload),
and just stick the payload into an 802.11 frame. I've seen
captures that show frames of that sort.
break; We also handle some odd form of encapsulation in which a
} complete Ethernet frame is encapsulated within an 802.11
/* I guess some bridges take Netware Ethernet_802_3 frames, data frame, with no 802.2 header. This has been seen
which are 802.3 frames (with a length field rather than from some hardware.
a type field, but with no 802.2 header in the payload),
and just stick the payload into an 802.11 frame. I've seen
captures that show frames of that sort.
We also handle some odd form of encapsulation in which a On top of that, at least at some point it appeared that
complete Ethernet frame is encapsulated within an 802.11 the OLPC XO sent out frames with two bytes of 0 between
data frame, with no 802.2 header. This has been seen the "end" of the 802.11 header and the beginning of
from some hardware. the payload. Something similar has also been observed
with Atheros chipsets. There the sequence control field
seems repeated.
On top of that, at least at some point it appeared that So, if the packet doesn't start with 0xaa 0xaa:
the OLPC XO sent out frames with two bytes of 0 between
the "end" of the 802.11 header and the beginning of
the payload. Something similar has also been observed
with Atheros chipsets. There the sequence control field
seems repeated.
So, if the packet doesn't start with 0xaa 0xaa: we first use the same scheme that linux-wlan-ng does to detect
those encapsulated Ethernet frames, namely looking to see whether
the frame either starts with 6 octets that match the destination
address from the 802.11 header or has 6 octets that match the
source address from the 802.11 header following the first 6 octets,
and, if so, treat it as an encapsulated Ethernet frame;
we first use the same scheme that linux-wlan-ng does to detect otherwise, we use the same scheme that we use in the Ethernet
those encapsulated Ethernet frames, namely looking to see whether dissector to recognize Netware 802.3 frames, namely checking
the frame either starts with 6 octets that match the destination whether the packet starts with 0xff 0xff and, if so, treat it
address from the 802.11 header or has 6 octets that match the as an encapsulated IPX frame, and then check whether the
source address from the 802.11 header following the first 6 octets, packet starts with 0x00 0x00 and, if so, treat it as an OLPC
and, if so, treat it as an encapsulated Ethernet frame; frame, or check the packet starts with the repetition of the
sequence control field and, if so, treat it as an Atheros frame. */
otherwise, we use the same scheme that we use in the Ethernet heur_dtbl_entry_t *hdtbl_entry;
dissector to recognize Netware 802.3 frames, namely checking if (dissector_try_heuristic(heur_subdissector_list, next_tvb, pinfo, tree, &hdtbl_entry, NULL)) {
whether the packet starts with 0xff 0xff and, if so, treat it pinfo->fragmented = save_fragmented;
as an encapsulated IPX frame, and then check whether the goto end_of_wlan; /* heuristics dissector handled it. */
packet starts with 0x00 0x00 and, if so, treat it as an OLPC }
frame, or check the packet starts with the repetition of the encap_type = ENCAP_802_2;
sequence control field and, if so, treat it as an Atheros frame. */ if (tvb_bytes_exist(next_tvb, 0, 2)) {
heur_dtbl_entry_t *hdtbl_entry; octet1 = tvb_get_guint8(next_tvb, 0);
if (dissector_try_heuristic(heur_subdissector_list, next_tvb, pinfo, tree, &hdtbl_entry, NULL)) { octet2 = tvb_get_guint8(next_tvb, 1);
pinfo->fragmented = save_fragmented; if ((octet1 != 0xaa) || (octet2 != 0xaa)) {
goto end_of_wlan; /* heuristics dissector handled it. */ if ((tvb_memeql(next_tvb, 6, (const guint8 *)pinfo->dl_src.data, 6) == 0) ||
} (tvb_memeql(next_tvb, 0, (const guint8 *)pinfo->dl_dst.data, 6) == 0))
encap_type = ENCAP_802_2; encap_type = ENCAP_ETHERNET;
if (tvb_bytes_exist(next_tvb, 0, 2)) { else if ((octet1 == 0xff) && (octet2 == 0xff))
octet1 = tvb_get_guint8(next_tvb, 0); encap_type = ENCAP_IPX;
octet2 = tvb_get_guint8(next_tvb, 1); else if (((octet1 == 0x00) && (octet2 == 0x00)) ||
if ((octet1 != 0xaa) || (octet2 != 0xaa)) { (((octet2 << 8) | octet1) == seq_control)) {
if ((tvb_memeql(next_tvb, 6, (const guint8 *)pinfo->dl_src.data, 6) == 0) || proto_tree_add_item(tree, hf_ieee80211_mysterious_olpc_stuff, next_tvb, 0, 2, ENC_NA);
(tvb_memeql(next_tvb, 0, (const guint8 *)pinfo->dl_dst.data, 6) == 0)) next_tvb = tvb_new_subset_remaining(next_tvb, 2);
encap_type = ENCAP_ETHERNET; }
else if ((octet1 == 0xff) && (octet2 == 0xff))
encap_type = ENCAP_IPX;
else if (((octet1 == 0x00) && (octet2 == 0x00)) ||
(((octet2 << 8) | octet1) == seq_control)) {
proto_tree_add_item(tree, hf_ieee80211_mysterious_olpc_stuff, next_tvb, 0, 2, ENC_NA);
next_tvb = tvb_new_subset_remaining(next_tvb, 2);
} }
} }
}
switch (encap_type) { switch (encap_type) {
case ENCAP_802_2: case ENCAP_802_2:
call_dissector(llc_handle, next_tvb, pinfo, tree); call_dissector(llc_handle, next_tvb, pinfo, tree);
break; break;
case ENCAP_ETHERNET: case ENCAP_ETHERNET:
call_dissector(eth_withoutfcs_handle, next_tvb, pinfo, tree); call_dissector(eth_withoutfcs_handle, next_tvb, pinfo, tree);
break; break;
case ENCAP_IPX: case ENCAP_IPX:
call_dissector(ipx_handle, next_tvb, pinfo, tree); call_dissector(ipx_handle, next_tvb, pinfo, tree);
break; break;
}
} }
break; break;