Mercurial > dropbear
view libtomcrypt/src/prngs/rng_get_bytes.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 | 6dba84798cd5 |
children |
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/* 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. */ #include "tomcrypt.h" #ifdef LTC_RNG_GET_BYTES /** @file rng_get_bytes.c portable way to get secure random bits to feed a PRNG (Tom St Denis) */ #if defined(LTC_DEVRANDOM) && !defined(_WIN32) /* on *NIX read /dev/random */ static unsigned long _rng_nix(unsigned char *buf, unsigned long len, void (*callback)(void)) { #ifdef LTC_NO_FILE LTC_UNUSED_PARAM(callback); LTC_UNUSED_PARAM(buf); LTC_UNUSED_PARAM(len); return 0; #else FILE *f; unsigned long x; LTC_UNUSED_PARAM(callback); #ifdef LTC_TRY_URANDOM_FIRST f = fopen("/dev/urandom", "rb"); if (f == NULL) #endif /* LTC_TRY_URANDOM_FIRST */ f = fopen("/dev/random", "rb"); if (f == NULL) { return 0; } /* disable buffering */ if (setvbuf(f, NULL, _IONBF, 0) != 0) { fclose(f); return 0; } x = (unsigned long)fread(buf, 1, (size_t)len, f); fclose(f); return x; #endif /* LTC_NO_FILE */ } #endif /* LTC_DEVRANDOM */ #if !defined(_WIN32_WCE) #define ANSI_RNG static unsigned long _rng_ansic(unsigned char *buf, unsigned long len, void (*callback)(void)) { clock_t t1; int l, acc, bits, a, b; l = len; bits = 8; acc = a = b = 0; while (len--) { if (callback != NULL) callback(); while (bits--) { do { t1 = XCLOCK(); while (t1 == XCLOCK()) a ^= 1; t1 = XCLOCK(); while (t1 == XCLOCK()) b ^= 1; } while (a == b); acc = (acc << 1) | a; } *buf++ = acc; acc = 0; bits = 8; } return l; } #endif /* Try the Microsoft CSP */ #if defined(_WIN32) || defined(_WIN32_WCE) #ifndef _WIN32_WINNT #define _WIN32_WINNT 0x0400 #endif #ifdef _WIN32_WCE #define UNDER_CE #define ARM #endif #define WIN32_LEAN_AND_MEAN #include <windows.h> #include <wincrypt.h> static unsigned long _rng_win32(unsigned char *buf, unsigned long len, void (*callback)(void)) { HCRYPTPROV hProv = 0; LTC_UNUSED_PARAM(callback); if (!CryptAcquireContext(&hProv, NULL, MS_DEF_PROV, PROV_RSA_FULL, (CRYPT_VERIFYCONTEXT | CRYPT_MACHINE_KEYSET)) && !CryptAcquireContext (&hProv, NULL, MS_DEF_PROV, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT | CRYPT_MACHINE_KEYSET | CRYPT_NEWKEYSET)) return 0; if (CryptGenRandom(hProv, len, buf) == TRUE) { CryptReleaseContext(hProv, 0); return len; } else { CryptReleaseContext(hProv, 0); return 0; } } #endif /* WIN32 */ /** Read the system RNG @param out Destination @param outlen Length desired (octets) @param callback Pointer to void function to act as "callback" when RNG is slow. This can be NULL @return Number of octets read */ unsigned long rng_get_bytes(unsigned char *out, unsigned long outlen, void (*callback)(void)) { unsigned long x; LTC_ARGCHK(out != NULL); #ifdef LTC_PRNG_ENABLE_LTC_RNG if (ltc_rng) { x = ltc_rng(out, outlen, callback); if (x != 0) { return x; } } #endif #if defined(_WIN32) || defined(_WIN32_WCE) x = _rng_win32(out, outlen, callback); if (x != 0) { return x; } #elif defined(LTC_DEVRANDOM) x = _rng_nix(out, outlen, callback); if (x != 0) { return x; } #endif #ifdef ANSI_RNG x = _rng_ansic(out, outlen, callback); if (x != 0) { return x; } #endif return 0; } #endif /* #ifdef LTC_RNG_GET_BYTES */ /* ref: $Format:%D$ */ /* git commit: $Format:%H$ */ /* commit time: $Format:%ai$ */