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Clean up the 'data' vs 'body' pointers in struct Packet.

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There's always been some confusion over exactly what it all means. I
haven't cleaned it up to the point of complete sensibleness, but I've
got it to a point where I can at least understand and document the
remaining non-sensibleness.

[originally from svn r10070]
This commit is contained in:
Simon Tatham 2013-11-17 14:04:18 +00:00
parent 1b3edafcff
commit 9f5d51a4ac
1 changed files with 41 additions and 8 deletions
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47
ssh.c
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@ -623,13 +623,13 @@ struct ssh_portfwd {
sfree((pf)->sserv), sfree((pf)->dserv)) : (void)0 ), sfree(pf) )
struct Packet {
long length; /* length of `data' actually used */
long length; /* length of packet: see below */
long forcepad; /* SSH-2: force padding to at least this length */
int type; /* only used for incoming packets */
unsigned long sequence; /* SSH-2 incoming sequence number */
unsigned char *data; /* allocated storage */
unsigned char *body; /* offset of payload within `data' */
long savedpos; /* temporary index into `data' (for strings) */
long savedpos; /* dual-purpose saved packet position: see below */
long maxlen; /* amount of storage allocated for `data' */
long encrypted_len; /* for SSH-2 total-size counting */
@ -639,6 +639,28 @@ struct Packet {
int logmode;
int nblanks;
struct logblank_t *blanks;
/*
* A note on the 'length' and 'savedpos' fields above.
*
* Incoming packets are set up so that pkt->length is measured
* relative to pkt->body, which itself points to a few bytes after
* pkt->data (skipping some uninteresting header fields including
* the packet type code). The ssh_pkt_get* functions all expect
* this setup, and they also use pkt->savedpos to indicate how far
* through the packet being decoded they've got - and that, too,
* is an offset from pkt->body rather than pkt->data.
*
* During construction of an outgoing packet, however, pkt->length
* is measured relative to the base pointer pkt->data, and
* pkt->body is not really used for anything until the packet is
* ready for sending. In this mode, pkt->savedpos is reused as a
* temporary variable by the addstring functions, which write out
* a string length field and then keep going back and updating it
* as more data is appended to the subsequent string data field;
* pkt->savedpos stores the offset (again relative to pkt->data)
* of the start of the string data field.
*/
};
static void ssh1_protocol(Ssh ssh, void *vin, int inlen,
@ -1234,6 +1256,11 @@ static struct Packet *ssh1_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
st->pktin->type = st->pktin->body[-1];
/*
* Now pktin->body and pktin->length identify the semantic content
* of the packet, excluding the initial type byte.
*/
/*
* Log incoming packet, possibly omitting sensitive fields.
*/
@ -1464,9 +1491,15 @@ static struct Packet *ssh2_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
}
}
st->pktin->savedpos = 6;
st->pktin->body = st->pktin->data;
/*
* pktin->body and pktin->length should identify the semantic
* content of the packet, excluding the initial type byte.
*/
st->pktin->type = st->pktin->data[5];
st->pktin->body = st->pktin->data + 6;
st->pktin->length = st->packetlen - 6 - st->pad;
st->pktin->savedpos = 0;
assert(st->pktin->length >= 0); /* one last double-check */
/*
* Log incoming packet, possibly omitting sensitive fields.
@ -1492,7 +1525,7 @@ static struct Packet *ssh2_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
log_packet(ssh->logctx, PKT_INCOMING, st->pktin->type,
ssh2_pkt_type(ssh->pkt_kctx, ssh->pkt_actx,
st->pktin->type),
st->pktin->data+6, st->pktin->length-6,
st->pktin->body, st->pktin->length,
nblanks, &blank, &st->pktin->sequence);
}
@ -5822,9 +5855,9 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
hash_string(ssh->kex->hash, ssh->exhash,
s->our_kexinit, s->our_kexinitlen);
sfree(s->our_kexinit);
if (pktin->length > 5)
/* Include the type byte in the hash of server's KEXINIT */
hash_string(ssh->kex->hash, ssh->exhash,
pktin->data + 5, pktin->length - 5);
pktin->body - 1, pktin->length + 1);
if (s->warn_kex) {
ssh_set_frozen(ssh, 1);