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Empty record limit.

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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.
This commit is contained in:
Adam Langley 2014-06-20 12:00:00 -07:00
parent d4b4f085d9
commit 48105fa215
3 changed files with 20 additions and 1 deletions
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19
ssl/s3_pkt.c
View File

@ -273,6 +273,12 @@ 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.
@ -293,6 +299,7 @@ static int ssl3_get_record(SSL *s)
short version;
unsigned mac_size, orig_len;
size_t extra;
unsigned empty_record_count = 0;
rr= &(s->s3->rrec);
sess=s->session;
@ -525,7 +532,17 @@ 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;
OPENSSL_PUT_ERROR(SSL, 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);

1
ssl/ssl.h
View File

@ -2974,5 +2974,6 @@ void ERR_load_SSL_strings(void);
#define SSL_R_CERT_CB_ERROR 428
#define SSL_R_DTLS_MESSAGE_TOO_BIG 429
#define SSL_R_INVALID_SRP_USERNAME 430
#define SSL_R_TOO_MANY_EMPTY_FRAGMENTS 431
#endif

1
ssl/ssl_error.c
View File

@ -475,6 +475,7 @@ const ERR_STRING_DATA SSL_error_string_data[] = {
{ERR_PACK(ERR_LIB_SSL, 0, SSL_R_TLS_INVALID_ECPOINTFORMAT_LIST), "TLS_INVALID_ECPOINTFORMAT_LIST"},
{ERR_PACK(ERR_LIB_SSL, 0, SSL_R_TLS_PEER_DID_NOT_RESPOND_WITH_CERTIFICATE_LIST), "TLS_PEER_DID_NOT_RESPOND_WITH_CERTIFICATE_LIST"},
{ERR_PACK(ERR_LIB_SSL, 0, SSL_R_TLS_RSA_ENCRYPTED_VALUE_LENGTH_IS_WRONG), "TLS_RSA_ENCRYPTED_VALUE_LENGTH_IS_WRONG"},
{ERR_PACK(ERR_LIB_SSL, 0, SSL_R_TOO_MANY_EMPTY_FRAGMENTS), "TOO_MANY_EMPTY_FRAGMENTS"},
{ERR_PACK(ERR_LIB_SSL, 0, SSL_R_TRIED_TO_USE_UNSUPPORTED_CIPHER), "TRIED_TO_USE_UNSUPPORTED_CIPHER"},
{ERR_PACK(ERR_LIB_SSL, 0, SSL_R_UNABLE_TO_DECODE_DH_CERTS), "UNABLE_TO_DECODE_DH_CERTS"},
{ERR_PACK(ERR_LIB_SSL, 0, SSL_R_UNABLE_TO_DECODE_ECDH_CERTS), "UNABLE_TO_DECODE_ECDH_CERTS"},