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CVE-2021-3634: Create a separate length for session_id

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Normally, the length of session_id and secret_hash is the same,
but if we will get into rekeying with a peer that changes preference
of key exchange algorithm, the new secret hash can be larger or
smaller than the previous session_id causing invalid reads or writes.

Resolves https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=35485

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
This commit is contained in:
Jakub Jelen
2021-06-23 13:16:33 +02:00
parent a3b2229a4e
commit f5211239f9
10 changed files with 23 additions and 18 deletions
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4
src/kex.c
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@@ -1233,11 +1233,13 @@ int ssh_make_sessionid(ssh_session session)
}
memcpy(session->next_crypto->session_id, session->next_crypto->secret_hash,
session->next_crypto->digest_len);
/* Initial length is the same as secret hash */
session->next_crypto->session_id_len = session->next_crypto->digest_len;
}
#ifdef DEBUG_CRYPTO
SSH_LOG(SSH_LOG_DEBUG, "Session hash: \n");
ssh_log_hexdump("secret hash", session->next_crypto->secret_hash, session->next_crypto->digest_len);
ssh_log_hexdump("session id", session->next_crypto->session_id, session->next_crypto->digest_len);
ssh_log_hexdump("session id", session->next_crypto->session_id, session->next_crypto->session_id_len);
#endif
rc = SSH_OK;