crypto: api - Fix race condition in larval lookup

crypto_larval_lookup should only return a larval if it created one.
Any larval created by another entity must be processed through
crypto_larval_wait before being returned.

Otherwise this will lead to a larval being killed twice, which
will most likely lead to a crash.

Cc: stable@vger.kernel.org
Reported-by: Kees Cook <keescook@chromium.org>
Tested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 6 insertions, 1 deletions

diff --git a/crypto/api.c b/crypto/api.c
index 320ea4d8a0f5..a2b39c5f3649 100644
--- a/crypto/api.c
+++ b/crypto/api.c
@@ -34,6 +34,8 @@ EXPORT_SYMBOL_GPL(crypto_alg_sem);
 BLOCKING_NOTIFIER_HEAD(crypto_chain);
 EXPORT_SYMBOL_GPL(crypto_chain);
 
+static struct crypto_alg *crypto_larval_wait(struct crypto_alg *alg);
+
 struct crypto_alg *crypto_mod_get(struct crypto_alg *alg)
 {
         return try_module_get(alg->cra_module) ? crypto_alg_get(alg) : NULL;
@@ -144,8 +146,11 @@ static struct crypto_alg *crypto_larval_add(const char *name, u32 type,
         }
         up_write(&crypto_alg_sem);
 
-        if (alg != &larval->alg)
+        if (alg != &larval->alg) {
                 kfree(larval);
+                if (crypto_is_larval(alg))
+                        alg = crypto_larval_wait(alg);
+        }
 
         return alg;
 }