This is a note to let you know that I've just added the patch titled

crypto: algapi - fix NULL dereference in crypto_remove_spawns()

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: crypto-algapi-fix-null-dereference-in-crypto_remove_spawns.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 9a00674213a3f00394f4e3221b88f2d21fc05789 Mon Sep 17 00:00:00 2001

From: Eric Biggers ebiggers@google.com Date: Fri, 29 Dec 2017 14:30:19 -0600 Subject: crypto: algapi - fix NULL dereference in crypto_remove_spawns()

From: Eric Biggers ebiggers@google.com

commit 9a00674213a3f00394f4e3221b88f2d21fc05789 upstream.

syzkaller triggered a NULL pointer dereference in crypto_remove_spawns() via a program that repeatedly and concurrently requests AEADs "authenc(cmac(des3_ede-asm),pcbc-aes-aesni)" and hashes "cmac(des3_ede)" through AF_ALG, where the hashes are requested as "untested" (CRYPTO_ALG_TESTED is set in ->salg_mask but clear in ->salg_feat; this causes the template to be instantiated for every request).

Although AF_ALG users really shouldn't be able to request an "untested" algorithm, the NULL pointer dereference is actually caused by a longstanding race condition where crypto_remove_spawns() can encounter an instance which has had spawn(s) "grabbed" but hasn't yet been registered, resulting in ->cra_users still being NULL.

We probably should properly initialize ->cra_users earlier, but that would require updating many templates individually. For now just fix the bug in a simple way that can easily be backported: make crypto_remove_spawns() treat a NULL ->cra_users list as empty.

Reported-by: syzbot syzkaller@googlegroups.com Signed-off-by: Eric Biggers ebiggers@google.com Signed-off-by: Herbert Xu herbert@gondor.apana.org.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- crypto/algapi.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)

--- a/crypto/algapi.c +++ b/crypto/algapi.c @@ -167,6 +167,18 @@ void crypto_remove_spawns(struct crypto_

spawn->alg = NULL; spawns = &inst->alg.cra_users; + + /* + * We may encounter an unregistered instance here, since + * an instance's spawns are set up prior to the instance + * being registered. An unregistered instance will have + * NULL ->cra_users.next, since ->cra_users isn't + * properly initialized until registration. But an + * unregistered instance cannot have any users, so treat + * it the same as ->cra_users being empty. + */ + if (spawns->next == NULL) + break; } } while ((spawns = crypto_more_spawns(alg, &stack, &top, &secondary_spawns)));

Patches currently in stable-queue which might be from ebiggers@google.com are

queue-4.14/crypto-algapi-fix-null-dereference-in-crypto_remove_spawns.patch