X-Git-Url: https://git.distorted.org.uk/u/mdw/putty/blobdiff_plain/6328ea7afa30e261e119bff240aede02f173e97b..98c84eb438c9d388460a921803f3bacaeb63a709:/ssh.c?ds=inline diff --git a/ssh.c b/ssh.c index 29f2a615..7b4bff46 100644 --- a/ssh.c +++ b/ssh.c @@ -122,6 +122,12 @@ #define SSH2_EXTENDED_DATA_STDERR 1 /* 0x1 */ +/* + * Various remote-bug flags. + */ +#define BUG_CHOKES_ON_SSH1_IGNORE 1 +#define BUG_SSH2_HMAC 2 + #define GET_32BIT(cp) \ (((unsigned long)(unsigned char)(cp)[0] << 24) | \ ((unsigned long)(unsigned char)(cp)[1] << 16) | \ @@ -173,9 +179,7 @@ const static struct ssh2_ciphers *ciphers[] = { }; const static struct ssh_kex *kex_algs[] = { -#ifdef DO_DIFFIE_HELLMAN_GEX &ssh_diffiehellman_gex, -#endif &ssh_diffiehellman }; const static struct ssh_signkey *hostkey_algs[] = { &ssh_rsa, &ssh_dss }; @@ -196,10 +200,12 @@ static int ssh_comp_none_block(unsigned char *block, int len, unsigned char **outblock, int *outlen) { return 0; } +static int ssh_comp_none_disable(void) { return 0; } const static struct ssh_compress ssh_comp_none = { "none", ssh_comp_none_init, ssh_comp_none_block, - ssh_comp_none_init, ssh_comp_none_block + ssh_comp_none_init, ssh_comp_none_block, + ssh_comp_none_disable }; extern const struct ssh_compress ssh_zlib; const static struct ssh_compress *compressions[] = { @@ -252,6 +258,7 @@ static unsigned char session_key[32]; static int ssh1_compressing; static int ssh_agentfwd_enabled; static int ssh_X11_fwd_enabled; +static int ssh_remote_bugs; static const struct ssh_cipher *cipher = NULL; static const struct ssh2_cipher *cscipher = NULL; static const struct ssh2_cipher *sccipher = NULL; @@ -659,15 +666,16 @@ static int s_wrpkt_prepare(void) { pktout.body[-1] = pktout.type; +#if 0 + debug(("Packet payload pre-compression:\n")); + for (i = -1; i < pktout.length; i++) + debug((" %02x", (unsigned char)pktout.body[i])); + debug(("\r\n")); +#endif + if (ssh1_compressing) { unsigned char *compblk; int complen; -#if 0 - debug(("Packet payload pre-compression:\n")); - for (i = -1; i < pktout.length; i++) - debug((" %02x", (unsigned char)pktout.body[i])); - debug(("\r\n")); -#endif zlib_compress_block(pktout.body-1, pktout.length+1, &compblk, &complen); ssh1_pktout_size(complen-1); @@ -1090,6 +1098,41 @@ static Bignum ssh2_pkt_getmp(void) { return b; } +/* + * Examine the remote side's version string and compare it against + * a list of known buggy implementations. + */ +static void ssh_detect_bugs(char *vstring) { + char *imp; /* pointer to implementation part */ + imp = vstring; + imp += strcspn(imp, "-"); + imp += strcspn(imp, "-"); + + ssh_remote_bugs = 0; + + if (!strcmp(imp, "1.2.18") || !strcmp(imp, "1.2.19") || + !strcmp(imp, "1.2.20") || !strcmp(imp, "1.2.21") || + !strcmp(imp, "1.2.22")) { + /* + * These versions don't support SSH1_MSG_IGNORE, so we have + * to use a different defence against password length + * sniffing. + */ + ssh_remote_bugs |= BUG_CHOKES_ON_SSH1_IGNORE; + logevent("We believe remote version has SSH1 ignore bug"); + } + + if (!strncmp(imp, "2.1.0", 5) || !strncmp(imp, "2.0.", 4) || + !strncmp(imp, "2.2.0", 5) || !strncmp(imp, "2.3.0", 5) || + !strncmp(imp, "2.1 ", 4)) { + /* + * These versions have the HMAC bug. + */ + ssh_remote_bugs |= BUG_SSH2_HMAC; + logevent("We believe remote version has SSH2 HMAC bug"); + } +} + static int do_ssh_init(unsigned char c) { static char *vsp; static char version[10]; @@ -1137,6 +1180,7 @@ static int do_ssh_init(unsigned char c) { *vsp = 0; sprintf(vlog, "Server version: %s", vstring); + ssh_detect_bugs(vstring); vlog[strcspn(vlog, "\r\n")] = '\0'; logevent(vlog); @@ -1835,38 +1879,65 @@ static int do_ssh1_login(unsigned char *in, int inlen, int ispkt) * N+7. This won't obscure the order of * magnitude of the password length, but it will * introduce a bit of extra uncertainty. + * + * A few servers (the old 1.2.18 through 1.2.22) + * can't deal with SSH1_MSG_IGNORE. For these + * servers, we need an alternative defence. We make + * use of the fact that the password is interpreted + * as a C string: so we can append a NUL, then some + * random data. */ - int bottom, top, pwlen, i; - char *randomstr; - - pwlen = strlen(password); - if (pwlen < 16) { - bottom = 1; - top = 15; + if (ssh_remote_bugs & BUG_CHOKES_ON_SSH1_IGNORE) { + char string[64]; + char *s; + int len; + + len = strlen(password); + if (len < sizeof(string)) { + s = string; + strcpy(string, password); + len++; /* cover the zero byte */ + while (len < sizeof(string)) { + string[len++] = (char)random_byte(); + } + } else { + s = password; + } + send_packet(pwpkt_type, PKT_INT, len, + PKT_DATA, s, len, PKT_END); } else { - bottom = pwlen &~ 7; - top = bottom + 7; - } + int bottom, top, pwlen, i; + char *randomstr; + + pwlen = strlen(password); + if (pwlen < 16) { + bottom = 0; /* zero length passwords are OK! :-) */ + top = 15; + } else { + bottom = pwlen &~ 7; + top = bottom + 7; + } - assert(pwlen >= bottom && pwlen <= top); + assert(pwlen >= bottom && pwlen <= top); - randomstr = smalloc(top+1); + randomstr = smalloc(top+1); - for (i = bottom; i <= top; i++) { - if (i == pwlen) - defer_packet(pwpkt_type, PKT_STR, password, PKT_END); - else { - for (j = 0; j < i; j++) { - do { - randomstr[j] = random_byte(); - } while (randomstr[j] == '\0'); + for (i = bottom; i <= top; i++) { + if (i == pwlen) + defer_packet(pwpkt_type, PKT_STR, password, PKT_END); + else { + for (j = 0; j < i; j++) { + do { + randomstr[j] = random_byte(); + } while (randomstr[j] == '\0'); + } + randomstr[i] = '\0'; + defer_packet(SSH1_MSG_IGNORE, + PKT_STR, randomstr, PKT_END); } - randomstr[i] = '\0'; - defer_packet(SSH1_MSG_IGNORE, - PKT_STR, randomstr, PKT_END); } + ssh_pkt_defersend(); } - ssh_pkt_defersend(); } else { send_packet(pwpkt_type, PKT_STR, password, PKT_END); } @@ -2258,7 +2329,7 @@ static void ssh2_mkkey(Bignum K, char *H, char *sessid, char chr, char *keyspace */ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt) { - static int i, j, len, nbits; + static int i, j, len, nbits, pbits; static char *str; static Bignum p, g, e, f, K; static int kex_init_value, kex_reply_value; @@ -2307,7 +2378,7 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt) /* * Be prepared to work around the buggy MAC problem. */ - if (cfg.buggymac) + if (cfg.buggymac || (ssh_remote_bugs & BUG_SSH2_HMAC)) maclist = buggymacs, nmacs = lenof(buggymacs); else maclist = macs, nmacs = lenof(macs); @@ -2481,30 +2552,34 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt) } /* + * Work out the number of bits of key we will need from the key + * exchange. We start with the maximum key length of either + * cipher... + */ + { + int csbits, scbits; + + csbits = cscipher_tobe->keylen; + scbits = sccipher_tobe->keylen; + nbits = (csbits > scbits ? csbits : scbits); + } + /* The keys only have 160-bit entropy, since they're based on + * a SHA-1 hash. So cap the key size at 160 bits. */ + if (nbits > 160) nbits = 160; + + /* * If we're doing Diffie-Hellman group exchange, start by * requesting a group. */ if (kex == &ssh_diffiehellman_gex) { - int csbits, scbits; - logevent("Doing Diffie-Hellman group exchange"); /* - * Work out number of bits. We start with the maximum key - * length of either cipher... - */ - csbits = cscipher_tobe->keylen; - scbits = sccipher_tobe->keylen; - nbits = (csbits > scbits ? csbits : scbits); - /* The keys only have 160-bit entropy, since they're based on - * a SHA-1 hash. So cap the key size at 160 bits. */ - if (nbits > 160) nbits = 160; - /* - * ... and then work out how big a DH group we will need to - * allow that much data. - */ - nbits = 512 << ((nbits-1) / 64); + * Work out how big a DH group we will need to allow that + * much data. + */ + pbits = 512 << ((nbits-1) / 64); ssh2_pkt_init(SSH2_MSG_KEX_DH_GEX_REQUEST); - ssh2_pkt_adduint32(nbits); + ssh2_pkt_adduint32(pbits); ssh2_pkt_send(); crWaitUntil(ispkt); @@ -2527,7 +2602,7 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt) /* * Now generate and send e for Diffie-Hellman. */ - e = dh_create_e(); + e = dh_create_e(nbits*2); ssh2_pkt_init(kex_init_value); ssh2_pkt_addmp(e); ssh2_pkt_send(); @@ -2545,7 +2620,7 @@ static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt) sha_string(&exhash, hostkeydata, hostkeylen); if (kex == &ssh_diffiehellman_gex) { - sha_uint32(&exhash, nbits); + sha_uint32(&exhash, pbits); sha_mpint(&exhash, p); sha_mpint(&exhash, g); }