Don't try to use zero-byte buffers.

crypto/bio/bio.h

@@ -618,6 +618,7 @@ int BIO_printf(BIO *bio, ...);
 #define BIO_R_ERROR_SETTING_NBIO_ON_ACCEPTED_SOCKET	 105
 #define BIO_R_ERROR_SETTING_NBIO_ON_ACCEPT_SOCKET	 106
 #define BIO_R_GETHOSTBYNAME_ADDR_IS_NOT_AF_INET		 107
+#define BIO_R_INVALID_ARGUMENT				 125
 #define BIO_R_INVALID_IP_ADDRESS			 108
 #define BIO_R_IN_USE					 123
 #define BIO_R_KEEPALIVE					 109

crypto/bio/bio_err.c

@@ -101,6 +101,7 @@ static ERR_STRING_DATA BIO_str_reasons[]=
 {BIO_R_ERROR_SETTING_NBIO_ON_ACCEPTED_SOCKET,"error setting nbio on accepted socket"},
 {BIO_R_ERROR_SETTING_NBIO_ON_ACCEPT_SOCKET,"error setting nbio on accept socket"},
 {BIO_R_GETHOSTBYNAME_ADDR_IS_NOT_AF_INET ,"gethostbyname addr is not af inet"},
+{BIO_R_INVALID_ARGUMENT                  ,"invalid argument"},
 {BIO_R_INVALID_IP_ADDRESS                ,"invalid ip address"},
 {BIO_R_IN_USE                            ,"in use"},
 {BIO_R_KEEPALIVE                         ,"keepalive"},

crypto/bio/bss_bio.c

@@ -280,6 +280,11 @@ static long bio_ctrl(BIO *bio, int cmd, long num, void *ptr)
 			BIOerr(BIO_F_BIO_CTRL, BIO_R_IN_USE);
 			ret = 0;
 			}
+		else if (num == 0)
+			{
+			BIOerr(BIO_F_BIO_CTRL, BIO_R_INVALID_ARGUMENT);
+			ret = 0;
+			}
 		else
 			{
 			size_t new_size = num;