Re: [PATCH v2 0/2] mac80211: use crypto shash for AES cmac
On Sun, Feb 05, 2017 at 03:23:26PM +, Ard Biesheuvel wrote: > NOTE: Jouni has been so kind to test patch #2, and confirmed that it is > working. > I have not tested patch #1 myself, mainly because the test methodology > requires downloading Ubuntu installer images, and I am currently on a > metered 3G connection (and will be for another couple of weeks) These v2 patches pass the test cases as well. (And you don't really need Ubuntu to run the hwsim test cases; any reasonably recent distribution that is capable of running kvm should work.) -- Jouni MalinenPGP id EFC895FA
Re: [RFC PATCH 0/2] mac80211: use crypto shash for AES cmac
On Sat, Feb 04, 2017 at 02:24:36PM +, Ard Biesheuvel wrote:
> There is another issue I spotted: the skcipher you allocate may be of
> the async variant, which may return from skcipher_encrypt() with
> -EINPROGRESS as soon as it has queued the request. Since you don't
> deal with that result, you should allocate a sync cipher explicitly:
> diff --git a/net/mac80211/fils_aead.c b/net/mac80211/fils_aead.c
> - tfm2 = crypto_alloc_skcipher("ctr(aes)", 0, 0);
> + tfm2 = crypto_alloc_skcipher("ctr(aes)", 0, CRYPTO_ALG_ASYNC);
> - tfm2 = crypto_alloc_skcipher("ctr(aes)", 0, 0);
> + tfm2 = crypto_alloc_skcipher("ctr(aes)", 0, CRYPTO_ALG_ASYNC);
Thanks! Can you send this as a full contribution or do you want me to
do that? I did run this through all the FILS test cases with
mac80211_hwsim.
> Thanks for the instructions and thanks for testing. If I manage to run
> this locally, I will follow up with an alternative patch #1 that
> switches FILS to use cmac(aes) as well (which looks reasonably
> feasible now that I understand the code)
If you have any issues in getting the hwsim test setup working, please
let me know. I'm trying to make it easy for anyone to run those tests in
hopes of improving quality of Linux WLAN contributions and what gets
applied into cfg80211 or mac80211 (or hostap.git for that matter). In
particular the latest step-by-step guide I added for the VM version (*)
was hoping to show how that can be done in 15 minutes from scratch..
(*) http://w1.fi/cgit/hostap/plain/tests/hwsim/vm/example-vm-setup.txt
--
Jouni MalinenPGP id EFC895FA
Re: [RFC PATCH 0/2] mac80211: use crypto shash for AES cmac
On Fri, Feb 03, 2017 at 09:55:36PM +, Ard Biesheuvel wrote: > OK, that looks like something I could figure out how to use. But are > you saying the CMAC code is never called in practice? It will get called if there is a frame that were to need to use BIP. There are some APs that do send broadcast addressed Deauthentication and Disassociation frames when terminating the network and those would get here. In theory, someone could come up with a new Action frame use case as well with a group addressed Robust Action frame, but no such thing is defined today. Anyway, this will be needed for certification purposes and to block DoS with broadcast addressed Deauthentication and Disassociation frames even if there is not really a common use case using BIP frames today. > I did spot something peculiar when looking at the code: if I am > reading the following sequence correctly (from > fils_encrypt_assoc_req()) > addr[0] = mgmt->sa; ... > addr[4] = capab; > len[4] = encr - capab; > > crypt_len = skb->data + skb->len - encr; > skb_put(skb, AES_BLOCK_SIZE); > return aes_siv_encrypt(assoc_data->fils_kek, assoc_data->fils_kek_len, > encr, crypt_len, 1, addr, len, encr); > > the addr[]/len[] arrays are populated with 5 (addr, len) pairs, but > only one is actually passed into aes_siv_encrypt()? This is actually > the main reason I stopped looking into whether I could convert it to > CMAC, because I couldn't figure it out. Argh.. Thanks for finding this! That is indeed supposed to have num_elems == 5. This "works" since the other end of the exchange is actually in user space (hostapd) and a similar error is there.. This comes from the development history of FILS support.. The draft standard changed this AES-SIV AAD design from P802.11ai/D7.0 to D8.0 from a single AAD vector with concatenated fields to separate vectors. Clearly I added the vectors here in addr[] and len[] arrays, but forgot to update the num_elems parameter in this direction (STA->AP); the other direction for Association Response frame is actually using correct number of AAD vectors. I'll fix this in hostapd and mac80211. I did not actually remember that the AP side was still in hostapd for FILS AEAD in case of mac80211, but with that in mind, the answer to your earlier question about testing these becomes much simpler.. All you need to do is this with hostap.git hwsim tests: hostap/tests/hwsim/vm$ ./vm-run.sh ap_cipher_bip fils_sk_erp Starting test run in a virtual machine ./run-all.sh: passing the following args to run-tests.py: ap_cipher_bip fils_sk_erp START ap_cipher_bip 1/2 PASS ap_cipher_bip 0.703048 2017-02-04 11:21:35.341174 START fils_sk_erp 2/2 PASS fils_sk_erp 0.667927 2017-02-04 11:21:36.029205 passed all 2 test case(s) ALL-PASSED ap_cipher_bip uses wlantest to verify the BIP (AES-128-CMAC) protection in the frames and fils_sk_erp goes through FILS AEAD exchange with one side of the operation in mac80211 and the other one in hostapd. This should be able to discover if something is broken in the AES related changes in crypto. And this particular example run here was with your two patches applied, to the proposed net/mac80211/aes_cmac.c change seems to work fine. -- Jouni MalinenPGP id EFC895FA
Re: [RFC PATCH 0/2] mac80211: use crypto shash for AES cmac
On Fri, Feb 03, 2017 at 07:25:53PM +, Ard Biesheuvel wrote: > The mac80211 aes_cmac code reimplements the CMAC algorithm based on the > core AES cipher, which is rather restrictive in how platforms can satisfy > the dependency on this algorithm. For instance, SIMD implementations may > have a considerable setup time, which cannot be amortized over the entire > input when calling into the crypto API one block at a time. Also, it prevents > the use of more secure fixed time implementations, since not all AES drivers > expose the cipher interface. > > So switch aes_cmac to use a cmac(aes) shash. This requires a preparatory > patch so that we can remove the open coded implementation, which it shares > with the fils aead driver. That driver could receive the same treatment, in > which case we could replace patch #1 with one that carries it over first. > > Note that this is an RFC. I have no idea how I would go about testing this > code, but I am on a mission to remove as many dependencies on the generic > AES cipher as I can. Neither the BIP nor FILS cases have any real speed requirements taken into account how rarely they end up being used in practice (there is really no use case for BIP today and FILS is used only once per association). That said, there should be no issues with moving these to a more generic mechanism assuming one is available now (I don't think that was the case when I was working on BIP and I was too lazy to figure out how to convert it or the newer FILS implementation).. mac80211_hwsim show allow some of the testing to be done with wlantest confirming the results in user space (*). I think that would cover all of BIP (net/mac80211/aes_cmac.c), but not FILS. For FILS, we do not currently have a convenient mechanism for running two different instances of kernel or even just mac80211 in the setup, so that would likely need testing with real WLAN hardware. I don't currently have a good setup for testing this (was using Backports-based solution in the past instead of full kernel build and Backports is a bit behind the current state..), but I guess I'll need to build something functional for this eventually.. Once that's in working condition on two devices, it would be straightforward to run a test (snapshot of hostap.git build to enable FILS functionality and go through one FILS authentication round).. Another alternative would be to extend wlantest to decrypt/validate FIPS AEAD use case based on keys exposed from hostapd or wpa_supplicant. There has not been sufficient use case for that so far and I have not bothered working on it yet. By the way, FILS AEAD uses SIV mode and I'm not sure it is supported in the current crypto code, so that would be one additional piece to take care of when considering net/mac80211/fils_aead.c conversion. (*) http://buildbot.w1.fi/hwsim/ http://w1.fi/cgit/hostap/tree/tests/hwsim/vm/example-vm-setup.txt -- Jouni MalinenPGP id EFC895FA
