From 42d7e1ff372f9e7e0fed9fe413e34de4b202987a Mon Sep 17 00:00:00 2001 From: Adam Langley Date: Wed, 20 Feb 2013 12:42:09 -0500 Subject: [PATCH 04/11] empty_record_limit Limit the number of empty records that will be processed consecutively in order to prevent ssl3_get_record from never returning. Reported by "oftc_must_be_destroyed" and George Kadianakis. --- ssl/s3_pkt.c | 19 ++++++++++++++++++- ssl/ssl.h | 1 + ssl/ssl_err.c | 1 + 3 files changed, 20 insertions(+), 1 deletion(-) diff --git a/ssl/s3_pkt.c b/ssl/s3_pkt.c index 8056291..e589409 100644 --- a/ssl/s3_pkt.c +++ b/ssl/s3_pkt.c @@ -272,6 +272,12 @@ int ssl3_read_n(SSL *s, int n, int max, int extend) return(n); } +/* MAX_EMPTY_RECORDS defines the number of consecutive, empty records that will + * be processed per call to ssl3_get_record. Without this limit an attacker + * could send empty records at a faster rate than we can process and cause + * ssl3_get_record to loop forever. */ +#define MAX_EMPTY_RECORDS 32 + /* Call this to get a new input record. * It will return <= 0 if more data is needed, normally due to an error * or non-blocking IO. @@ -292,6 +298,7 @@ static int ssl3_get_record(SSL *s) short version; unsigned mac_size; size_t extra; + unsigned empty_record_count = 0; rr= &(s->s3->rrec); sess=s->session; @@ -522,7 +529,17 @@ printf("\n"); s->packet_length=0; /* just read a 0 length packet */ - if (rr->length == 0) goto again; + if (rr->length == 0) + { + empty_record_count++; + if (empty_record_count > MAX_EMPTY_RECORDS) + { + al=SSL_AD_UNEXPECTED_MESSAGE; + SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_TOO_MANY_EMPTY_FRAGMENTS); + goto f_err; + } + goto again; + } #if 0 fprintf(stderr, "Ultimate Record type=%d, Length=%d\n", rr->type, rr->length); diff --git a/ssl/ssl.h b/ssl/ssl.h index e14a8d4..938f65a 100644 --- a/ssl/ssl.h +++ b/ssl/ssl.h @@ -2820,6 +2820,7 @@ void ERR_load_SSL_strings(void); #define SSL_R_TLS_INVALID_ECPOINTFORMAT_LIST 157 #define SSL_R_TLS_PEER_DID_NOT_RESPOND_WITH_CERTIFICATE_LIST 233 #define SSL_R_TLS_RSA_ENCRYPTED_VALUE_LENGTH_IS_WRONG 234 +#define SSL_R_TOO_MANY_EMPTY_FRAGMENTS 388 #define SSL_R_TRIED_TO_USE_UNSUPPORTED_CIPHER 235 #define SSL_R_UNABLE_TO_DECODE_DH_CERTS 236 #define SSL_R_UNABLE_TO_DECODE_ECDH_CERTS 313 diff --git a/ssl/ssl_err.c b/ssl/ssl_err.c index d8b4d70..fd571a3 100644 --- a/ssl/ssl_err.c +++ b/ssl/ssl_err.c @@ -575,6 +575,7 @@ static ERR_STRING_DATA SSL_str_reasons[]= {ERR_REASON(SSL_R_TLS_INVALID_ECPOINTFORMAT_LIST),"tls invalid ecpointformat list"}, {ERR_REASON(SSL_R_TLS_PEER_DID_NOT_RESPOND_WITH_CERTIFICATE_LIST),"tls peer did not respond with certificate list"}, {ERR_REASON(SSL_R_TLS_RSA_ENCRYPTED_VALUE_LENGTH_IS_WRONG),"tls rsa encrypted value length is wrong"}, +{ERR_REASON(SSL_R_TOO_MANY_EMPTY_FRAGMENTS),"too many empty fragments"}, {ERR_REASON(SSL_R_TRIED_TO_USE_UNSUPPORTED_CIPHER),"tried to use unsupported cipher"}, {ERR_REASON(SSL_R_UNABLE_TO_DECODE_DH_CERTS),"unable to decode dh certs"}, {ERR_REASON(SSL_R_UNABLE_TO_DECODE_ECDH_CERTS),"unable to decode ecdh certs"}, -- 1.8.2.1