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ssh: checking and showing Message Authentication Code

This commit is contained in:
Jérôme HAMM 2022-01-18 21:51:11 +01:00 committed by A Wireshark GitLab Utility
parent 7ea9bab84b
commit 41b442d9c0
1 changed files with 104 additions and 1 deletions
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105
epan/dissectors/packet-ssh.c
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@ -98,6 +98,7 @@ typedef struct {
#define SSH_KEX_HASH_SHA256 2
#define DIGEST_MAX_SIZE 48
typedef struct _ssh_message_info_t {
guint32 sequence_number;
@ -107,6 +108,7 @@ typedef struct _ssh_message_info_t {
gint id; /**< Identifies the exact message within a frame
(there can be multiple records in a frame). */
struct _ssh_message_info_t* next;
guint8 calc_mac[DIGEST_MAX_SIZE];
} ssh_message_info_t;
typedef struct {
@ -214,6 +216,7 @@ static int hf_ssh_payload = -1;
static int hf_ssh_encrypted_packet = -1;
static int hf_ssh_padding_string = -1;
static int hf_ssh_mac_string = -1;
static int hf_ssh_mac_status = -1;
static int hf_ssh_direction = -1;
/* Message codes */
@ -316,6 +319,7 @@ static gint ett_ssh2 = -1;
static expert_field ei_ssh_packet_length = EI_INIT;
static expert_field ei_ssh_invalid_keylen = EI_INIT;
static expert_field ei_ssh_mac_bad = EI_INIT;
static gboolean ssh_desegment = TRUE;
@ -530,6 +534,9 @@ static guint ssh_decrypt_packet(tvbuff_t *tvb, packet_info *pinfo,
static gboolean ssh_decrypt_chacha20(gcry_cipher_hd_t hd, guint32 seqnr,
guint32 counter, const guchar *ctext, guint ctext_len,
guchar *plain, guint plain_len);
static proto_item * ssh_tree_add_mac(proto_tree *tree, tvbuff_t *tvb, const guint offset, const guint mac_len,
const int hf_mac, const int hf_mac_status, struct expert_field* bad_checksum_expert,
packet_info *pinfo, const guint8 * calc_mac, const guint flags);
static int ssh_dissect_decrypted_packet(tvbuff_t *tvb, packet_info *pinfo,
struct ssh_peer_data *peer_data, proto_tree *tree,
@ -2302,6 +2309,8 @@ ssh_decrypt_packet(tvbuff_t *tvb, packet_info *pinfo,
if (gcry_mac_verify(mac_hd, mac, mac_len)) {
g_debug("ssh: MAC does not match");
}
size_t buflen = DIGEST_MAX_SIZE;
gcry_mac_read(mac_hd, message->calc_mac, &buflen);
message->plain_data = plain;
message->data_len = message_length + 4;
@ -2313,12 +2322,101 @@ ssh_decrypt_packet(tvbuff_t *tvb, packet_info *pinfo,
if(plain){
ssh_dissect_decrypted_packet(tvb, pinfo, peer_data, tree, plain, message_length+4);
ssh_tree_add_mac(tree, tvb, offset + 4 + message_length, mac_len, hf_ssh_mac_string, hf_ssh_mac_status, &ei_ssh_mac_bad, pinfo, message->calc_mac,
PROTO_CHECKSUM_VERIFY|PROTO_CHECKSUM_IN_CKSUM);
}
offset += message_length + peer_data->mac_length + 4;
return offset;
}
proto_item *
ssh_tree_add_mac(proto_tree *tree, tvbuff_t *tvb, const guint offset, const guint mac_len,
const int hf_mac, const int hf_mac_status, struct expert_field* bad_checksum_expert,
packet_info *pinfo, const guint8 * calc_mac, const guint flags)
{
// header_field_info *hfinfo = proto_registrar_get_nth(hf_checksum);
proto_item* ti = NULL;
proto_item* ti2;
gboolean incorrect_mac = TRUE;
gchar *mac;
// DISSECTOR_ASSERT_HINT(hfinfo != NULL, "Not passed hfi!");
/*
if (flags & PROTO_CHECKSUM_NOT_PRESENT) {
ti = proto_tree_add_uint_format_value(tree, hf_checksum, tvb, offset, len, 0, "[missing]");
proto_item_set_generated(ti);
if (hf_checksum_status != -1) {
ti2 = proto_tree_add_uint(tree, hf_checksum_status, tvb, offset, len, PROTO_CHECKSUM_E_NOT_PRESENT);
proto_item_set_generated(ti2);
}
return ti;
}
*/
mac = (gchar *)tvb_get_ptr(tvb, offset, mac_len);
if (flags & PROTO_CHECKSUM_GENERATED) {
// ti = proto_tree_add_uint(tree, hf_checksum, tvb, offset, len, computed_checksum);
// proto_item_set_generated(ti);
} else {
ti = proto_tree_add_item(tree, hf_mac, tvb, offset, mac_len, ENC_NA);
if (flags & PROTO_CHECKSUM_VERIFY) {
if (flags & (PROTO_CHECKSUM_IN_CKSUM|PROTO_CHECKSUM_ZERO)) {
if (!memcmp(mac, calc_mac, mac_len)) {
proto_item_append_text(ti, " [correct]");
if (hf_mac_status != -1) {
ti2 = proto_tree_add_uint(tree, hf_mac_status, tvb, offset, 0, PROTO_CHECKSUM_E_GOOD);
proto_item_set_generated(ti2);
}
incorrect_mac = FALSE;
} else if (flags & PROTO_CHECKSUM_IN_CKSUM) {
// computed_checksum = in_cksum_shouldbe(checksum, computed_checksum);
}
} else {
if (!memcmp(mac, calc_mac, mac_len)) {
proto_item_append_text(ti, " [correct]");
if (hf_mac_status != -1) {
ti2 = proto_tree_add_uint(tree, hf_mac_status, tvb, offset, 0, PROTO_CHECKSUM_E_GOOD);
proto_item_set_generated(ti2);
}
incorrect_mac = FALSE;
}
}
if (incorrect_mac) {
if (hf_mac_status != -1) {
ti2 = proto_tree_add_uint(tree, hf_mac_status, tvb, offset, 0, PROTO_CHECKSUM_E_BAD);
proto_item_set_generated(ti2);
}
if (flags & PROTO_CHECKSUM_ZERO) {
proto_item_append_text(ti, " [incorrect]");
if (bad_checksum_expert != NULL)
expert_add_info_format(pinfo, ti, bad_checksum_expert, "%s", expert_get_summary(bad_checksum_expert));
} else {
gchar *data = (gchar *)wmem_alloc(wmem_packet_scope(), mac_len*2 + 1);
// proto_item_append_text(ti, " incorrect, should be TODO");
static const char h2a[] = "0123456789abcdef";
for(guint macCnt=0;macCnt<mac_len;macCnt++){
data[macCnt*2+0] = h2a[(calc_mac[macCnt] >> 4) & 0xF];
data[macCnt*2+1] = h2a[(calc_mac[macCnt] >> 0) & 0xF];
}
data[mac_len*2] = 0;
proto_item_append_text(ti, " incorrect, computed %s", data);
if (bad_checksum_expert != NULL)
expert_add_info_format(pinfo, ti, bad_checksum_expert, "%s", expert_get_summary(bad_checksum_expert));
}
}
} else {
if (hf_mac_status != -1) {
proto_item_append_text(ti, " [unverified]");
ti2 = proto_tree_add_uint(tree, hf_mac_status, tvb, offset, 0, PROTO_CHECKSUM_E_UNVERIFIED);
proto_item_set_generated(ti2);
}
}
}
return ti;
}
static gboolean
ssh_decrypt_chacha20(gcry_cipher_hd_t hd,
guint32 seqnr, guint32 counter, const guchar *ctext, guint ctext_len,
@ -2813,6 +2911,10 @@ proto_register_ssh(void)
FT_BYTES, BASE_NONE, NULL, 0x0,
"Message authentication code", HFILL }},
{ &hf_ssh_mac_status,
{ "MAC Status", "ssh.mac.status", FT_UINT8, BASE_NONE, VALS(proto_checksum_vals), 0x0,
NULL, HFILL }},
{ &hf_ssh_direction,
{ "Direction", "ssh.direction",
FT_BOOLEAN, BASE_NONE, NULL, 0x0,
@ -3211,7 +3313,8 @@ proto_register_ssh(void)
static ei_register_info ei[] = {
{ &ei_ssh_packet_length, { "ssh.packet_length.error", PI_PROTOCOL, PI_WARN, "Overly large number", EXPFILL }},
{ &ei_ssh_invalid_keylen, { "ssh.key_length.error", PI_PROTOCOL, PI_ERROR, "Invalid key length", EXPFILL }}
{ &ei_ssh_invalid_keylen, { "ssh.key_length.error", PI_PROTOCOL, PI_ERROR, "Invalid key length", EXPFILL }},
{ &ei_ssh_mac_bad, { "ssh.mac_bad.expert", PI_CHECKSUM, PI_ERROR, "Bad MAC", EXPFILL }},
};
module_t *ssh_module;