Mercurial > dropbear
view ltc_prng.c @ 1788:1fc0012b9c38
Fix handling of replies to global requests (#112)
The current code assumes that all global requests want / need a reply.
This isn't always true and the request itself indicates if it wants a
reply or not.
It causes a specific problem with [email protected] messages.
These are sent by OpenSSH after authentication to inform the client of
potential other host keys for the host. This can be used to add a new
type of host key or to rotate host keys.
The initial information message from the server is sent as a global
request, but with want_reply set to false. This means that the server
doesn't expect an answer to this message. Instead the client needs to
send a prove request as a reply if it wants to receive proof of
ownership for the host keys.
The bug doesn't cause any current problems with due to how OpenSSH
treats receiving the failure message. It instead treats it as a
keepalive message and further ignores it.
Arguably this is a protocol violation though of Dropbear and it is only
accidental that it doesn't cause a problem with OpenSSH.
The bug was found when adding host keys support to libssh, which is more
strict protocol wise and treats the unexpected failure message an error,
also see https://gitlab.com/libssh/libssh-mirror/-/merge_requests/145
for more information.
The fix here is to honor the want_reply flag in the global request and
to only send a reply if the other side expects a reply.
author | Dirkjan Bussink <d.bussink@gmail.com> |
---|---|
date | Thu, 10 Dec 2020 16:13:13 +0100 |
parents | d68d61e7056a |
children |
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/* Copied from libtomcrypt/src/prngs/sprng.c and modified to * use Dropbear's genrandom(). */ /* LibTomCrypt, modular cryptographic library -- Tom St Denis * * LibTomCrypt is a library that provides various cryptographic * algorithms in a highly modular and flexible manner. * * The library is free for all purposes without any express * guarantee it works. * * Tom St Denis, [email protected], http://libtomcrypt.com */ #include "includes.h" #include "dbrandom.h" #include "ltc_prng.h" /** @file sprng.c Secure PRNG, Tom St Denis */ /* A secure PRNG using the RNG functions. Basically this is a * wrapper that allows you to use a secure RNG as a PRNG * in the various other functions. */ #if DROPBEAR_LTC_PRNG /** Start the PRNG @param prng [out] The PRNG state to initialize @return CRYPT_OK if successful */ int dropbear_prng_start(prng_state* UNUSED(prng)) { return CRYPT_OK; } /** Add entropy to the PRNG state @param in The data to add @param inlen Length of the data to add @param prng PRNG state to update @return CRYPT_OK if successful */ int dropbear_prng_add_entropy(const unsigned char* UNUSED(in), unsigned long UNUSED(inlen), prng_state* UNUSED(prng)) { return CRYPT_OK; } /** Make the PRNG ready to read from @param prng The PRNG to make active @return CRYPT_OK if successful */ int dropbear_prng_ready(prng_state* UNUSED(prng)) { return CRYPT_OK; } /** Read from the PRNG @param out Destination @param outlen Length of output @param prng The active PRNG to read from @return Number of octets read */ unsigned long dropbear_prng_read(unsigned char* out, unsigned long outlen, prng_state* UNUSED(prng)) { LTC_ARGCHK(out != NULL); genrandom(out, outlen); return outlen; } /** Terminate the PRNG @param prng The PRNG to terminate @return CRYPT_OK if successful */ int dropbear_prng_done(prng_state* UNUSED(prng)) { return CRYPT_OK; } /** Export the PRNG state @param out [out] Destination @param outlen [in/out] Max size and resulting size of the state @param prng The PRNG to export @return CRYPT_OK if successful */ int dropbear_prng_export(unsigned char* UNUSED(out), unsigned long* outlen, prng_state* UNUSED(prng)) { LTC_ARGCHK(outlen != NULL); *outlen = 0; return CRYPT_OK; } /** Import a PRNG state @param in The PRNG state @param inlen Size of the state @param prng The PRNG to import @return CRYPT_OK if successful */ int dropbear_prng_import(const unsigned char* UNUSED(in), unsigned long UNUSED(inlen), prng_state* UNUSED(prng)) { return CRYPT_OK; } /** PRNG self-test @return CRYPT_OK if successful, CRYPT_NOP if self-testing has been disabled */ int dropbear_prng_test(void) { return CRYPT_OK; } const struct ltc_prng_descriptor dropbear_prng_desc = { "dropbear_prng", 0, dropbear_prng_start, dropbear_prng_add_entropy, dropbear_prng_ready, dropbear_prng_read, dropbear_prng_done, dropbear_prng_export, dropbear_prng_import, dropbear_prng_test }; #endif /* DROPBEAR_LTC_PRNG */