> From: openssl-users [mailto:openssl-users-bounces@xxxxxxxxxxx] On Behalf Of Matthew > Sent: Friday, August 30, 2019 23:06 Welcome to the list. When posting, please remember to tell us what version of OpenSSL you're using, and what platform you're on. Since you're talking about C#, I'll assume the platform is Windows. And I'll assume you're working with OpenSSL 1.1.1c, because that would be the sensible thing to do. But it would be better if I didn't have to make either assumption. > I stepped through both the working unit test and the non-working one in order to find > differences in the result. What I have found is that, in ssl3_read_n, the call to > BIO_read (line 300 in rec_layer_s3.c) returns -1. > ret = BIO_read(s->rbio, pkt + len + left, max - left); > At this line, pkt is a char[8], len and left = 0 and max = 16717 I don't think pkt is a char[8]. It's defined at the top of ssl3_read_n as unsigne char *pkt. And it had better not be a char[8], since 1) plain char and unsigned char are not the same type, and 2) if max - left is 16717, then you have potential for a massive buffer overflow. > I'm curious as to why the "data" argument is not a pointer to a buffer, but rather > the result of an addition. Maybe my C isnt strong enough... It's a pointer into a buffer (specifically, in this case, a pointer to the start of a buffer). In C, adding an integer type to a pointer results in a pointer value. That is, in fact, basic C. (At least you're only reading C, not writing it. I have in recent days seen C code posted by people who really need to put the language down and back away slowly. C should not be used by people who don't know the language very well.) > Going even further down the stack, I finally end up at the bottom: > static int mem_read(BIO *b, char *out, int outl) > ... > } else if (bm->length == 0) { > ret = b->num; > if (ret != 0) > BIO_set_retry_read(b); > } > return ret; > At this point, ret = -1... So b->num == -1 when you arrived here with bm->length == 0. The num field is initialized to -1 when a memory BIO is initialized (mem_init in bss_mem.c). And the length is 0, which means there's no data in the BIO. I don't know (without reading through your code, which I don't have time to do right now) why you're using a memory BIO, or how you've initialized it. It looks like you've simply never put any data into it. -- Michael Wojcik Distinguished Engineer, Micro Focus
