crypto: user - Fix crypto_alg_match race
The function crypto_alg_match returns an algorithm without taking
any references on it. This means that the algorithm can be freed
at any time, therefore all users of crypto_alg_match are buggy.
This patch fixes this by taking a reference count on the algorithm
to prevent such races.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/crypto/crypto_user.c b/crypto/crypto_user.c
index eab2497..41dfe76 100644
--- a/crypto/crypto_user.c
+++ b/crypto/crypto_user.c
@@ -62,10 +62,14 @@
else if (!exact)
match = !strcmp(q->cra_name, p->cru_name);
- if (match) {
- alg = q;
- break;
- }
+ if (!match)
+ continue;
+
+ if (unlikely(!crypto_mod_get(q)))
+ continue;
+
+ alg = q;
+ break;
}
up_read(&crypto_alg_sem);
@@ -205,9 +209,10 @@
if (!alg)
return -ENOENT;
+ err = -ENOMEM;
skb = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_ATOMIC);
if (!skb)
- return -ENOMEM;
+ goto drop_alg;
info.in_skb = in_skb;
info.out_skb = skb;
@@ -215,6 +220,10 @@
info.nlmsg_flags = 0;
err = crypto_report_alg(alg, &info);
+
+drop_alg:
+ crypto_mod_put(alg);
+
if (err)
return err;
@@ -284,6 +293,7 @@
up_write(&crypto_alg_sem);
+ crypto_mod_put(alg);
crypto_remove_final(&list);
return 0;
@@ -294,6 +304,7 @@
{
struct crypto_alg *alg;
struct crypto_user_alg *p = nlmsg_data(nlh);
+ int err;
if (!netlink_capable(skb, CAP_NET_ADMIN))
return -EPERM;
@@ -310,13 +321,19 @@
* if we try to unregister. Unregistering such an algorithm without
* removing the module is not possible, so we restrict to crypto
* instances that are build from templates. */
+ err = -EINVAL;
if (!(alg->cra_flags & CRYPTO_ALG_INSTANCE))
- return -EINVAL;
+ goto drop_alg;
- if (atomic_read(&alg->cra_refcnt) != 1)
- return -EBUSY;
+ err = -EBUSY;
+ if (atomic_read(&alg->cra_refcnt) > 2)
+ goto drop_alg;
- return crypto_unregister_instance((struct crypto_instance *)alg);
+ err = crypto_unregister_instance((struct crypto_instance *)alg);
+
+drop_alg:
+ crypto_mod_put(alg);
+ return err;
}
static struct crypto_alg *crypto_user_skcipher_alg(const char *name, u32 type,
@@ -395,8 +412,10 @@
return -EINVAL;
alg = crypto_alg_match(p, exact);
- if (alg)
+ if (alg) {
+ crypto_mod_put(alg);
return -EEXIST;
+ }
if (strlen(p->cru_driver_name))
name = p->cru_driver_name;
