Hi Stephan, On 16 June 2016 at 10:05, Stephan Mueller <smueller@xxxxxxxxxx> wrote: > Am Dienstag, 14. Juni 2016, 09:42:34 schrieb Andrew Zaborowski: > > Hi Andrew, > >> > >> > I think we have agreed on dropping the length enforcement at the interface >> > level. >> >> Separately from this there's a problem with the user being unable to >> know if the algorithm is going to fail because of destination buffer >> size != key size (including kernel users). For RSA, the qat >> implementation will fail while the software implementation won't. For >> pkcs1pad(...) there's currently just one implementation but the user >> can't assume that. > > If I understand your issue correctly, my initial code requiring the caller to > provide sufficient memory would have covered the issue, right? This isn't an issue with AF_ALG, I should have changed the subject line perhaps. In this case it's an inconsistency between some implementations and the documentation (header comment). It affects users accessing the cipher through AF_ALG but also directly. > If so, we seem > to have implementations which can handle shorter buffer sizes and some which > do not. Should a caller really try to figure the right buffer size out? Why > not requiring a mandatory buffer size and be done with it? I.e. what is the > gain to allow shorter buffer sizes (as pointed out by Mat)? It's that client code doesn't need an intermediate layer with an additional buffer and a memcpy to provide a sensible API. If the code wants to decrypt a 32-byte Digest Info structure with a given key or a reference to a key it makes no sense, logically or in terms of performance, for it to provide a key-sized buffer. In the case of the userspace interface I think it's also rare for a recv() or read() on Linux to require a buffer larger than it's going to use, correct me if i'm wrong. (I.e. fail if given a 32-byte buffer, return 32 bytes of data anyway) Turning your questino around is there a gain from requiring larger buffers? Best regards -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
