| Message ID | 20171229203019.1413-1-ebiggers3@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Herbert Xu |
| Headers | show |
On Fri, Dec 29, 2017 at 02:30:19PM -0600, Eric Biggers wrote: > From: Eric Biggers <ebiggers@google.com> > > 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> > Cc: stable@vger.kernel.org > Signed-off-by: Eric Biggers <ebiggers@google.com> Patch applied. Thanks.
diff --git a/crypto/algapi.c b/crypto/algapi.c index 9895cafcce7e..395b082d03a9 100644 --- a/crypto/algapi.c +++ b/crypto/algapi.c @@ -166,6 +166,18 @@ void crypto_remove_spawns(struct crypto_alg *alg, struct list_head *list, 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)));