Remove instances in libssl of the constant 28 (for size of IPv4 header + UDP) and instead use the value provided by the underlying BIO. Also provide some new DTLS_CTRLs so that the library user can set the mtu without needing to know this constant. These new DTLS_CTRLs provide the capability to set the link level mtu to be used (i.e. including this IP/UDP overhead). The previous DTLS_CTRLs required the library user to subtract this overhead first. Reviewed-by: Tim Hudson <tjh@openssl.org>
diff --git a/ssl/d1_both.c b/ssl/d1_both.c index 9a981e8..bea975b 100644 --- a/ssl/d1_both.c +++ b/ssl/d1_both.c
@@ -156,9 +156,9 @@ static unsigned char bitmask_end_values[] = {0xff, 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f}; /* XDTLS: figure out the right values */ -static const unsigned int g_probable_mtu[] = {1500 - 28, 512 - 28, 256 - 28}; +static const unsigned int g_probable_mtu[] = {1500, 512, 256}; -static unsigned int dtls1_guess_mtu(unsigned int curr_mtu); +static void dtls1_guess_mtu(SSL *s); static void dtls1_fix_message_header(SSL *s, unsigned long frag_off, unsigned long frag_len); static unsigned char *dtls1_write_message_header(SSL *s, @@ -226,18 +226,24 @@ static void dtls1_query_mtu(SSL *s) { + if(s->d1->link_mtu) + { + s->d1->mtu = s->d1->link_mtu-BIO_dgram_get_mtu_overhead(SSL_get_wbio(s)); + s->d1->link_mtu = 0; + } + /* AHA! Figure out the MTU, and stick to the right size */ - if (s->d1->mtu < dtls1_min_mtu() && !(SSL_get_options(s) & SSL_OP_NO_QUERY_MTU)) + if (s->d1->mtu < dtls1_min_mtu(s) && !(SSL_get_options(s) & SSL_OP_NO_QUERY_MTU)) { s->d1->mtu = BIO_ctrl(SSL_get_wbio(s), BIO_CTRL_DGRAM_QUERY_MTU, 0, NULL); /* I've seen the kernel return bogus numbers when it doesn't know * (initial write), so just make sure we have a reasonable number */ - if (s->d1->mtu < dtls1_min_mtu()) + if (s->d1->mtu < dtls1_min_mtu(s)) { s->d1->mtu = 0; - s->d1->mtu = dtls1_guess_mtu(s->d1->mtu); + dtls1_guess_mtu(s); BIO_ctrl(SSL_get_wbio(s), BIO_CTRL_DGRAM_SET_MTU, s->d1->mtu, NULL); } @@ -275,7 +281,7 @@ } #endif - OPENSSL_assert(s->d1->mtu >= dtls1_min_mtu()); /* should have something reasonable now */ + OPENSSL_assert(s->d1->mtu >= dtls1_min_mtu(s)); /* should have something reasonable now */ if ( s->init_off == 0 && type == SSL3_RT_HANDSHAKE) OPENSSL_assert(s->init_num == @@ -1299,26 +1305,40 @@ return p; } -unsigned int -dtls1_min_mtu(void) +unsigned int +dtls1_link_min_mtu(void) { return (g_probable_mtu[(sizeof(g_probable_mtu) / sizeof(g_probable_mtu[0])) - 1]); } -static unsigned int -dtls1_guess_mtu(unsigned int curr_mtu) +unsigned int +dtls1_min_mtu(SSL *s) { + return dtls1_link_min_mtu()-BIO_dgram_get_mtu_overhead(SSL_get_wbio(s)); + } + +static void +dtls1_guess_mtu(SSL *s) + { + unsigned int curr_mtu; unsigned int i; + unsigned int mtu_ovr; + + curr_mtu = s->d1->mtu; + mtu_ovr = BIO_dgram_get_mtu_overhead(SSL_get_wbio(s)); if ( curr_mtu == 0 ) - return g_probable_mtu[0] ; - - for ( i = 0; i < sizeof(g_probable_mtu)/sizeof(g_probable_mtu[0]); i++) - if ( curr_mtu > g_probable_mtu[i]) - return g_probable_mtu[i]; - - return curr_mtu; + { + curr_mtu = g_probable_mtu[0] - mtu_ovr; + } + else + { + for ( i = 0; i < sizeof(g_probable_mtu)/sizeof(g_probable_mtu[0]); i++) + if ( curr_mtu > g_probable_mtu[i] - mtu_ovr) + return g_probable_mtu[i] - mtu_ovr; + } + s->d1->mtu = curr_mtu; } void
diff --git a/ssl/d1_lib.c b/ssl/d1_lib.c index 09268b8..5b3de08 100644 --- a/ssl/d1_lib.c +++ b/ssl/d1_lib.c
@@ -139,6 +139,9 @@ d1->cookie_len = sizeof(s->d1->cookie); } + d1->link_mtu = 0; + d1->mtu = 0; + if( ! d1->unprocessed_rcds.q || ! d1->processed_rcds.q || ! d1->buffered_messages || ! d1->sent_messages || ! d1->buffered_app_data.q) { @@ -234,6 +237,7 @@ pqueue sent_messages; pqueue buffered_app_data; unsigned int mtu; + unsigned int link_mtu; if (s->d1) { @@ -243,6 +247,7 @@ sent_messages = s->d1->sent_messages; buffered_app_data = s->d1->buffered_app_data.q; mtu = s->d1->mtu; + link_mtu = s->d1->link_mtu; dtls1_clear_queues(s); @@ -256,6 +261,7 @@ if (SSL_get_options(s) & SSL_OP_NO_QUERY_MTU) { s->d1->mtu = mtu; + s->d1->link_mtu = link_mtu; } s->d1->unprocessed_rcds.q = unprocessed_rcds; @@ -312,6 +318,25 @@ } return 0; /* Unexpected state; fail closed. */ + /* Just one protocol version is supported so far; + * fail closed if the version is not as expected. */ + return s->version == DTLS_MAX_VERSION; + case DTLS_CTRL_SET_LINK_MTU: + if (larg < (long)dtls1_link_min_mtu()) + return 0; + s->d1->link_mtu = larg; + return 1; + case DTLS_CTRL_GET_LINK_MIN_MTU: + return (long)dtls1_link_min_mtu(); + case SSL_CTRL_SET_MTU: + /* + * We may not have a BIO set yet so can't call dtls1_min_mtu() + * We'll have to make do with dtls1_link_min_mtu() and max overhead + */ + if (larg < (long)dtls1_link_min_mtu() - DTLS1_MAX_MTU_OVERHEAD) + return 0; + s->d1->mtu = larg; + return larg; default: ret = ssl3_ctrl(s, cmd, larg, parg); break;
diff --git a/ssl/dtls1.h b/ssl/dtls1.h index af86f60..96f7334 100644 --- a/ssl/dtls1.h +++ b/ssl/dtls1.h
@@ -121,6 +121,9 @@ #define DTLS1_SCTP_AUTH_LABEL "EXPORTER_DTLS_OVER_SCTP" #endif +/* Max MTU overhead we know about so far is 40 for IPv6 + 8 for UDP */ +#define DTLS1_MAX_MTU_OVERHEAD 48 + typedef struct dtls1_bitmap_st { unsigned long map; /* track 32 packets on 32-bit systems @@ -235,6 +238,7 @@ /* Is set when listening for new connections with dtls1_listen() */ unsigned int listen; + unsigned int link_mtu; /* max on-the-wire DTLS packet size */ unsigned int mtu; /* max DTLS packet size */ struct hm_header_st w_msg_hdr;
diff --git a/ssl/ssl.h b/ssl/ssl.h index bc4cd0d..104e4f1 100644 --- a/ssl/ssl.h +++ b/ssl/ssl.h
@@ -787,6 +787,10 @@ SSL_ctrl((ssl),SSL_CTRL_MODE,0,NULL) #define SSL_set_mtu(ssl, mtu) \ SSL_ctrl((ssl),SSL_CTRL_SET_MTU,(mtu),NULL) +#define DTLS_set_link_mtu(ssl, mtu) \ + SSL_ctrl((ssl),DTLS_CTRL_SET_LINK_MTU,(mtu),NULL) +#define DTLS_get_link_min_mtu(ssl) \ + SSL_ctrl((ssl),DTLS_CTRL_GET_LINK_MIN_MTU,0,NULL) #define SSL_get_secure_renegotiation_support(ssl) \ SSL_ctrl((ssl), SSL_CTRL_GET_RI_SUPPORT, 0, NULL) @@ -1844,6 +1848,8 @@ #define SSL_CTRL_SET_DH_AUTO 118 #define SSL_CTRL_CHECK_PROTO_VERSION 119 +#define DTLS_CTRL_SET_LINK_MTU 120 +#define DTLS_CTRL_GET_LINK_MIN_MTU 121 #define SSL_CERT_SET_FIRST 1
diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c index 43204de..f45b6dd 100644 --- a/ssl/ssl_lib.c +++ b/ssl/ssl_lib.c
@@ -1129,18 +1129,6 @@ l=s->max_cert_list; s->max_cert_list=larg; return(l); - case SSL_CTRL_SET_MTU: -#ifndef OPENSSL_NO_DTLS1 - if (larg < (long)dtls1_min_mtu()) - return 0; -#endif - - if (SSL_IS_DTLS(s)) - { - s->d1->mtu = larg; - return larg; - } - return 0; case SSL_CTRL_SET_MAX_SEND_FRAGMENT: if (larg < 512 || larg > SSL3_RT_MAX_PLAIN_LENGTH) return 0;
diff --git a/ssl/ssl_locl.h b/ssl/ssl_locl.h index 60f8107..ffbf75b 100644 --- a/ssl/ssl_locl.h +++ b/ssl/ssl_locl.h
@@ -1218,7 +1218,8 @@ int dtls1_is_timer_expired(SSL *s); void dtls1_double_timeout(SSL *s); int dtls1_send_newsession_ticket(SSL *s); -unsigned int dtls1_min_mtu(void); +unsigned int dtls1_min_mtu(SSL *s); +unsigned int dtls1_link_min_mtu(void); void dtls1_hm_fragment_free(hm_fragment *frag); /* some client-only functions */