Re: [PATCH 1/6] ksmbd: fix global-out-of-bounds in smb2_find_context_vals

[Sergey Senozhatsky <senozhatsky@chromium.org>]

On (23/05/06 00:11), Namjae Jeon wrote:
> From: Pumpkin <cc85nod@gmail.com>
> 
> If the length of CreateContext name is larger than the tag, it will access
> the data following the tag and trigger KASAN global-out-of-bounds.
> 
> Currently all CreateContext names are defined as string, so we can use
> strcmp instead of memcmp to avoid the out-of-bound access.

[..]

> +++ b/fs/ksmbd/oplock.c
> @@ -1492,7 +1492,7 @@ struct create_context *smb2_find_context_vals(void *open_req, const char *tag)
>  			return ERR_PTR(-EINVAL);
>  
>  		name = (char *)cc + name_off;
> -		if (memcmp(name, tag, name_len) == 0)
> +		if (!strcmp(name, tag))
>  			return cc;
>  
>  		remain_len -= next;

I'm slightly surprised that that huge `if` before memcmp() doesn't catch
it

		if ((next & 0x7) != 0 ||
		    next > remain_len ||
		    name_off != offsetof(struct create_context, Buffer) ||
		    name_len < 4 ||
		    name_off + name_len > cc_len ||
		    (value_off & 0x7) != 0 ||
		    (value_off && (value_off < name_off + name_len)) ||
		    ((u64)value_off + value_len > cc_len))
			return ERR_PTR(-EINVAL);

Is that because we should check `name_len` instead of `name_off + name_len`?
IOW

		if (name_len != cc_len)
			return ERR_PTR();