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>

1 files changed, 29 insertions, 10 deletions

diff --git a/crypto/crypto_user.c b/crypto/crypto_user.c
index eab249723830..41dfe762b7fb 100644
--- a/crypto/crypto_user.c
+++ b/crypto/crypto_user.c
@@ -62,10 +62,14 @@ static struct crypto_alg *crypto_alg_match(struct crypto_user_alg *p, int exact)
                 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 @@ static int crypto_report(struct sk_buff *in_skb, struct nlmsghdr *in_nlh,
         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 @@ static int crypto_report(struct sk_buff *in_skb, struct nlmsghdr *in_nlh,
         info.nlmsg_flags = 0;
 
         err = crypto_report_alg(alg, &info);
+
+drop_alg:
+        crypto_mod_put(alg);
+
         if (err)
                 return err;
 
@@ -284,6 +293,7 @@ static int crypto_update_alg(struct sk_buff *skb, struct nlmsghdr *nlh,
 
         up_write(&crypto_alg_sem);
 
+        crypto_mod_put(alg);
         crypto_remove_final(&list);
 
         return 0;
@@ -294,6 +304,7 @@ static int crypto_del_alg(struct sk_buff *skb, struct nlmsghdr *nlh,
 {
         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 @@ static int crypto_del_alg(struct sk_buff *skb, struct nlmsghdr *nlh,
          * 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 @@ static int crypto_add_alg(struct sk_buff *skb, struct nlmsghdr *nlh,
                 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;