| Message ID | 20180313042907.29598-1-tycho@tycho.ws (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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 <tycho@tycho.ws> > CC: David Howells <dhowells@redhat.com> > CC: James Morris <jmorris@namei.org> > CC: "Serge E. Hallyn" <serge@hallyn.com> > CC: Jason A. Donenfeld <Jason@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
Hi Eric, On Wed, Mar 14, 2018 at 06:51:39PM -0700, Eric Biggers wrote: > 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 <tycho@tycho.ws> > > CC: David Howells <dhowells@redhat.com> > > CC: James Morris <jmorris@namei.org> > > CC: "Serge E. Hallyn" <serge@hallyn.com> > > CC: Jason A. Donenfeld <Jason@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, I've fixed this for v2. Cheers, Tycho
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; }
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 <tycho@tycho.ws> CC: David Howells <dhowells@redhat.com> CC: James Morris <jmorris@namei.org> CC: "Serge E. Hallyn" <serge@hallyn.com> CC: Jason A. Donenfeld <Jason@zx2c4.com> --- security/keys/big_key.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)