On Thu, Jun 29, 2023 at 07:15:21AM +0900, Tetsuo Handa wrote: > On 2023/06/29 6:03, Jakub Kicinski wrote: > > On Wed, 28 Jun 2023 22:48:01 +0900 Tetsuo Handa wrote: > >> syzbot is reporting uninit-value at aes_encrypt(), for block cipher assumes > >> that bytes to encrypt/decrypt is multiple of block size for that cipher but > >> tls_alloc_encrypted_msg() is not initializing padding bytes when > >> required_size is not multiple of block cipher's block size. > > > > Sounds odd, so crypto layer reads beyond what we submitted as > > the buffer? I don't think the buffer needs to be aligned, so > > the missing bits may well fall into a different (unmapped?) page. > > Since passing __GFP_ZERO to skb_page_frag_refill() hides this problem, > I think that crypto layer is reading up to block size when requested > size is not multiple of block size. > > > > > This needs more careful investigation. Always zeroing the input > > is just covering up the real issue. > > Since block cipher needs to read up to block size, someone has to initialize > padding bytes. I guess that crypto API caller is responsible for allocating > and initializing padding bytes, otherwise such crypto API caller will fail to > encrypt/decrypt last partial bytes which are not multiple of cipher's block > size. > > Which function in this report is responsible for initializing padding bytes? According to the sample crash report from https://syzkaller.appspot.com/bug?extid=828dfc12440b4f6f305d, the uninitialized memory access happens while the TLS layer is doing an AES-CCM encryption operation. CCM supports arbitrarily-aligned additional authenticated data and plaintext/ciphertext. Also, an encryption with crypto_aead_encrypt() reads exactly 'assoclen + cryptlen' bytes from the 'src' scatterlist; it's not supposed to ever go past that, even if the data isn't "block aligned". The "aead" API (include/crypto/aead.h) is still confusing and hard to use correctly, though, mainly because of the weird scatterlist layout it expects with the AAD and plaintext/ciphertext concatenated to each other. I wouldn't be surprised if the TLS layer is making some error. What is the exact sequence of crypto_aead_* calls that results in this issue? - Eric
