Don't allow too many consecutive warning alerts

Certain warning alerts are ignored if they are received. This can mean that
no progress will be made if one peer continually sends those warning alerts.
Implement a count so that we abort the connection if we receive too many.

Issue reported by Shi Lei.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(cherry picked from commit af58be768ebb690f78530f796e92b8ae5c9a4401)

6 files changed, 38 insertions, 0 deletions

diff --git a/include/openssl/ssl.h b/include/openssl/ssl.h
index 41cb36e943..440b9a0d74 100644
--- a/include/openssl/ssl.h
+++ b/include/openssl/ssl.h
@@ -2482,6 +2482,7 @@ int ERR_load_SSL_strings(void);
 # define SSL_R_TLS_HEARTBEAT_PENDING                      366
 # define SSL_R_TLS_ILLEGAL_EXPORTER_LABEL                 367
 # define SSL_R_TLS_INVALID_ECPOINTFORMAT_LIST             157
+# define SSL_R_TOO_MANY_WARN_ALERTS                       409
 # define SSL_R_UNABLE_TO_FIND_ECDH_PARAMETERS             314
 # define SSL_R_UNABLE_TO_FIND_PUBLIC_KEY_PARAMETERS       239
 # define SSL_R_UNABLE_TO_LOAD_SSL3_MD5_ROUTINES           242
diff --git a/ssl/record/rec_layer_d1.c b/ssl/record/rec_layer_d1.c
index cd582f3222..2455c2bd12 100644
--- a/ssl/record/rec_layer_d1.c
+++ b/ssl/record/rec_layer_d1.c
@@ -443,6 +443,14 @@ int dtls1_read_bytes(SSL *s, int type, int *recvd_type, unsigned char *buf,
         }
     }
 
+    /*
+     * Reset the count of consecutive warning alerts if we've got a non-empty
+     * record that isn't an alert.
+     */
+    if (SSL3_RECORD_get_type(rr) != SSL3_RT_ALERT
+            && SSL3_RECORD_get_length(rr) != 0)
+        s->rlayer.alert_count = 0;
+
     /* we now have a packet which can be read and processed */
 
     if (s->s3->change_cipher_spec /* set when we receive ChangeCipherSpec,
@@ -722,6 +730,14 @@ int dtls1_read_bytes(SSL *s, int type, int *recvd_type, unsigned char *buf,
 
         if (alert_level == SSL3_AL_WARNING) {
             s->s3->warn_alert = alert_descr;
+
+            s->rlayer.alert_count++;
+            if (s->rlayer.alert_count == MAX_WARN_ALERT_COUNT) {
+                al = SSL_AD_UNEXPECTED_MESSAGE;
+                SSLerr(SSL_F_DTLS1_READ_BYTES, SSL_R_TOO_MANY_WARN_ALERTS);
+                goto f_err;
+            }
+
             if (alert_descr == SSL_AD_CLOSE_NOTIFY) {
 #ifndef OPENSSL_NO_SCTP
                 /*
diff --git a/ssl/record/rec_layer_s3.c b/ssl/record/rec_layer_s3.c
index 46870c054b..abde9d4a73 100644
--- a/ssl/record/rec_layer_s3.c
+++ b/ssl/record/rec_layer_s3.c
@@ -1063,6 +1063,14 @@ int ssl3_read_bytes(SSL *s, int type, int *recvd_type, unsigned char *buf,
     } while (num_recs == 0);
     rr = &rr[curr_rec];
 
+    /*
+     * Reset the count of consecutive warning alerts if we've got a non-empty
+     * record that isn't an alert.
+     */
+    if (SSL3_RECORD_get_type(rr) != SSL3_RT_ALERT
+            && SSL3_RECORD_get_length(rr) != 0)
+        s->rlayer.alert_count = 0;
+
     /* we now have a packet which can be read and processed */
 
     if (s->s3->change_cipher_spec /* set when we receive ChangeCipherSpec,
@@ -1333,6 +1341,14 @@ int ssl3_read_bytes(SSL *s, int type, int *recvd_type, unsigned char *buf,
         if (alert_level == SSL3_AL_WARNING) {
             s->s3->warn_alert = alert_descr;
             SSL3_RECORD_set_read(rr);
+
+            s->rlayer.alert_count++;
+            if (s->rlayer.alert_count == MAX_WARN_ALERT_COUNT) {
+                al = SSL_AD_UNEXPECTED_MESSAGE;
+                SSLerr(SSL_F_SSL3_READ_BYTES, SSL_R_TOO_MANY_WARN_ALERTS);
+                goto f_err;
+            }
+
             if (alert_descr == SSL_AD_CLOSE_NOTIFY) {
                 s->shutdown |= SSL_RECEIVED_SHUTDOWN;
                 return (0);
diff --git a/ssl/record/record.h b/ssl/record/record.h
index a093aed48f..3e1530f139 100644
--- a/ssl/record/record.h
+++ b/ssl/record/record.h
@@ -178,6 +178,8 @@ typedef struct record_layer_st {
     unsigned char write_sequence[SEQ_NUM_SIZE];
     /* Set to true if this is the first record in a connection */
     unsigned int is_first_record;
+    /* Count of the number of consecutive warning alerts received */
+    unsigned int alert_count;
     DTLS_RECORD_LAYER *d;
 } RECORD_LAYER;
 
diff --git a/ssl/record/record_locl.h b/ssl/record/record_locl.h
index 52e59e46d5..b69afd8002 100644
--- a/ssl/record/record_locl.h
+++ b/ssl/record/record_locl.h
@@ -14,6 +14,8 @@
  *                                                                           *
  *****************************************************************************/
 
+#define MAX_WARN_ALERT_COUNT    5
+
 /* Functions/macros provided by the RECORD_LAYER component */
 
 #define RECORD_LAYER_get_rbuf(rl)               (&(rl)->rbuf)
diff --git a/ssl/ssl_err.c b/ssl/ssl_err.c
index 1fddda612a..85cb489c9d 100644
--- a/ssl/ssl_err.c
+++ b/ssl/ssl_err.c
@@ -614,6 +614,7 @@ static ERR_STRING_DATA SSL_str_reasons[] = {
      "tls illegal exporter label"},
     {ERR_REASON(SSL_R_TLS_INVALID_ECPOINTFORMAT_LIST),
      "tls invalid ecpointformat list"},
+    {ERR_REASON(SSL_R_TOO_MANY_WARN_ALERTS), "too many warn alerts"},
     {ERR_REASON(SSL_R_UNABLE_TO_FIND_ECDH_PARAMETERS),
      "unable to find ecdh parameters"},
     {ERR_REASON(SSL_R_UNABLE_TO_FIND_PUBLIC_KEY_PARAMETERS),