Hello Stephen, Before getting to business I wish to offer my thanks for hosting the kernel crypto documentation on your web site at chronox.de. It has proven very useful to me :-) On Mon, Jan 9, 2017 at 12:23 PM, Stephan Müller <smueller@xxxxxxxxxx> wrote: > Am Sonntag, 8. Januar 2017, 15:45:37 CET schrieb Gilad Ben-Yossef: > > Hi Gilad, > >> ahash_request_set_callback(req, 0, NULL, NULL); > >> >> Would anyone be kind enough to enlighten me? > > The documentation got out of sync with the real world. I will file a patch for > that shortly. > > The ahash API works identically to the async skcipher API for which you find > an example in the api-samples.rst. There you see that with the set_callback, a > function is registered that is triggered upon completion of the operation. > > Thus, use the callback example you find for skcipher for your ahash operation > and you get an async operation. Thank you very much for pointing out the skcipher example. It is very helpful. However, I suspect there is something a miss here beyond documentation: There is (quite a lot of) kernel code calling ahash_request_set_callback() with a NULL callback and consequently not performing any synchronization in the completion of the hashing operations. See for example crypt_iv_essiv_init() in drivers/md/dm-crypt.c Other similar call sites can be found at block/drbd/drbd_worker.c, net/ppp/ppp_mppe.c, net/wireless/intersil/orinoco/mic.c, scsi/iscsi_tcp.c, target/iscsi/iscsi_target_login.c As far as I could tell the code in crypto/ahash.c does not take any special consideration of the case where a NULL call back function has been set and at least one of the underlying ahash algorithm provider will crash if used like this. This seems broken to me. I would be very happy to offer to fix the broken call sites, if you can only confirm my understanding that indeed cases which register a NULL callback are broken and it is not just a misunderstanding on my part. Many thanks, Gilad -- Gilad Ben-Yossef Chief Coffee Drinker "If you take a class in large-scale robotics, can you end up in a situation where the homework eats your dog?" -- Jean-Baptiste Queru -- 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
