From cc0663f697b05ed121a728241f0502250429802d Mon Sep 17 00:00:00 2001 From: Simon Cornish <7t9jna402@sneakemail.com> Date: Fri, 14 Feb 2020 14:16:09 -0800 Subject: [PATCH] Handle max_fragment_length overflow for DTLS Allow for encryption overhead in early DTLS size check and send overflow if validated record is too long Reviewed-by: Matt Caswell Reviewed-by: Tomas Mraz (Merged from https://github.com/openssl/openssl/pull/11096) --- ssl/record/ssl3_record.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/ssl/record/ssl3_record.c b/ssl/record/ssl3_record.c index 36e8d86902..a5ef78dec9 100644 --- a/ssl/record/ssl3_record.c +++ b/ssl/record/ssl3_record.c @@ -1630,6 +1630,7 @@ int dtls1_process_record(SSL *s, DTLS1_BITMAP *bitmap) int imac_size; size_t mac_size; unsigned char md[EVP_MAX_MD_SIZE]; + size_t max_plain_length = SSL3_RT_MAX_PLAIN_LENGTH; rr = RECORD_LAYER_get_rrec(&s->rlayer); sess = s->session; @@ -1797,7 +1798,12 @@ int dtls1_process_record(SSL *s, DTLS1_BITMAP *bitmap) } } - if (rr->length > SSL3_RT_MAX_PLAIN_LENGTH) { + /* use current Max Fragment Length setting if applicable */ + if (s->session != NULL && USE_MAX_FRAGMENT_LENGTH_EXT(s->session)) + max_plain_length = GET_MAX_FRAGMENT_LENGTH(s->session); + + /* send overflow if the plaintext is too long now it has passed MAC */ + if (rr->length > max_plain_length) { SSLfatal(s, SSL_AD_RECORD_OVERFLOW, SSL_F_DTLS1_PROCESS_RECORD, SSL_R_DATA_LENGTH_TOO_LONG); return 0; @@ -1941,7 +1947,7 @@ int dtls1_get_record(SSL *s) /* If received packet overflows own-client Max Fragment Length setting */ if (s->session != NULL && USE_MAX_FRAGMENT_LENGTH_EXT(s->session) - && rr->length > GET_MAX_FRAGMENT_LENGTH(s->session)) { + && rr->length > GET_MAX_FRAGMENT_LENGTH(s->session) + SSL3_RT_MAX_ENCRYPTED_OVERHEAD) { /* record too long, silently discard it */ rr->length = 0; rr->read = 1; -- 2.25.1