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kex: server fix for first_kex_packet_follows

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Ensure to honor the 'first_kex_packet_follow' field when processing
KEXINIT messages in the 'ssh_packet_kexinit' callback.  Until now
libssh would assume that this field is always unset (zero).  But
some clients may set this (dropbear at or beyond version 2013.57),
and it needs to be included when computing the session ID.

Also include logic for handling wrongly-guessed key exchange algorithms.
Save whether a client's guess is wrong in a new field in the session
struct: when set, the next KEX_DHINIT message to be processed will be
ignored per RFC 4253, 7.1.

While here, update both 'ssh_packet_kexinit' and 'make_sessionid' to
use softabs with a 4 space indent level throughout, and also convert
various error-checking to store intermediate values into an explicit
'rc'.

Signed-off-by: Jon Simons <jon@jonsimons.org>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
This commit is contained in:
Jon Simons
2014-04-09 15:24:04 -07:00
committed by Andreas Schneider
parent ad1313c2e5
commit 5865b9436f
4 changed files with 366 additions and 247 deletions
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9
src/server.c
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@@ -174,6 +174,15 @@ SSH_PACKET_CALLBACK(ssh_packet_kexdh_init){
SSH_LOG(SSH_LOG_RARE,"Invalid state for SSH_MSG_KEXDH_INIT");
goto error;
}
/* If first_kex_packet_follows guess was wrong, ignore this message. */
if (session->first_kex_follows_guess_wrong != 0) {
SSH_LOG(SSH_LOG_RARE, "first_kex_packet_follows guess was wrong, "
"ignoring first SSH_MSG_KEXDH_INIT message");
session->first_kex_follows_guess_wrong = 0;
goto error;
}
switch(session->next_crypto->kex_type){
case SSH_KEX_DH_GROUP1_SHA1:
case SSH_KEX_DH_GROUP14_SHA1: