On Mon, Mar 12, 2018 at 10:29:06PM -0600, Tycho Andersen wrote: > We're interested in getting rid of all of the stack allocated arrays in the > kernel [1]. This patch removes one in keys by switching to malloc/free. > Note that we use kzalloc, to avoid leaking the nonce. I'm not sure this is > really necessary, but extra paranoia seems prudent. > > Manually tested using the program from the add_key man page to trigger > big_key. > > [1]: https://lkml.org/lkml/2018/3/7/621 > > Signed-off-by: Tycho Andersen <ty...@tycho.ws> > CC: David Howells <dhowe...@redhat.com> > CC: James Morris <jmor...@namei.org> > CC: "Serge E. Hallyn" <se...@hallyn.com> > CC: Jason A. Donenfeld <ja...@zx2c4.com> > --- > security/keys/big_key.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/security/keys/big_key.c b/security/keys/big_key.c > index fa728f662a6f..70f9f785c59d 100644 > --- a/security/keys/big_key.c > +++ b/security/keys/big_key.c > @@ -108,13 +108,18 @@ static int big_key_crypt(enum big_key_op op, struct > big_key_buf *buf, size_t dat > * an .update function, so there's no chance we'll wind up reusing the > * key to encrypt updated data. Simply put: one key, one encryption. > */ > - u8 zero_nonce[crypto_aead_ivsize(big_key_aead)]; > + u8 *zero_nonce; > + > + zero_nonce = kzalloc(crypto_aead_ivsize(big_key_aead), GFP_KERNEL); > + if (!zero_nonce) > + return -ENOMEM; > > aead_req = aead_request_alloc(big_key_aead, GFP_KERNEL); > - if (!aead_req) > + if (!aead_req) { > + kfree(zero_nonce); > return -ENOMEM; > + } > > - memset(zero_nonce, 0, sizeof(zero_nonce)); > aead_request_set_crypt(aead_req, buf->sg, buf->sg, datalen, zero_nonce); > aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, > NULL); > aead_request_set_ad(aead_req, 0); > @@ -131,6 +136,7 @@ static int big_key_crypt(enum big_key_op op, struct > big_key_buf *buf, size_t dat > error: > mutex_unlock(&big_key_aead_lock); > aead_request_free(aead_req); > + kzfree(zero_nonce); > return ret;
A dynamic allocation here doesn't make sense -- the algorithm is hard-coded to AES-GCM, so the IV size is fixed. You should just include <crypto/gcm.h> and use GCM_AES_IV_LEN. As a sanity check you can add 'BUG_ON(crypto_aead_ivsize(big_key_aead) != GCM_AES_IV_LEN' to big_key_init(). kzfree() also doesn't make sense since the nonce is not secret information. Thanks, Eric
