path: root/crypto
diff options
authorEric Biggers <ebiggers@google.com>2017-12-29 14:30:19 -0600
committerHerbert Xu <herbert@gondor.apana.org.au>2018-01-05 18:41:52 +1100
commit9a00674213a3f00394f4e3221b88f2d21fc05789 (patch)
tree3376c611066a95dbbb9762fe358db012ac39c6fc /crypto
parent2973633e9f09311e849f975d969737af81a521ff (diff)
crypto: algapi - fix NULL dereference in crypto_remove_spawns()
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> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Diffstat (limited to 'crypto')
1 files changed, 12 insertions, 0 deletions
diff --git a/crypto/algapi.c b/crypto/algapi.c
index 60d7366ed343..9a636f961572 100644
--- a/crypto/algapi.c
+++ b/crypto/algapi.c
@@ -167,6 +167,18 @@ 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,