2019-07-24 12:36:56

by Jia-Ju Bai

Subject: [PATCH] net: ceph: Fix a possible null-pointer dereference in ceph_crypto_key_destroy()

In set_secret(), key->tfm is assigned to NULL on line 55, and then
ceph_crypto_key_destroy(key) is executed.

ceph_crypto_key_destroy(key)
crypto_free_sync_skcipher(key->tfm)
crypto_skcipher_tfm(tfm)
return &tfm->base;

Thus, a possible null-pointer dereference may occur.

To fix this bug, key->tfm is checked before calling
crypto_free_sync_skcipher().

This bug is found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <[email protected]>
---
net/ceph/crypto.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ceph/crypto.c b/net/ceph/crypto.c
index 5d6724cee38f..ac28463bcfd8 100644
--- a/net/ceph/crypto.c
+++ b/net/ceph/crypto.c
@@ -136,7 +136,8 @@ void ceph_crypto_key_destroy(struct ceph_crypto_key *key)
if (key) {
kfree(key->key);
key->key = NULL;
- crypto_free_sync_skcipher(key->tfm);
+ if (key->tfm)
+ crypto_free_sync_skcipher(key->tfm);
key->tfm = NULL;
}
}
--
2.17.0

2019-07-30 14:10:25

by Ilya Dryomov

Subject: Re: [PATCH] net: ceph: Fix a possible null-pointer dereference in ceph_crypto_key_destroy()

On Wed, Jul 24, 2019 at 11:43 AM Jia-Ju Bai <[email protected]> wrote:
>
> In set_secret(), key->tfm is assigned to NULL on line 55, and then
> ceph_crypto_key_destroy(key) is executed.
>
> ceph_crypto_key_destroy(key)
> crypto_free_sync_skcipher(key->tfm)
> crypto_skcipher_tfm(tfm)
> return &tfm->base;
>
> Thus, a possible null-pointer dereference may occur.
>
> To fix this bug, key->tfm is checked before calling
> crypto_free_sync_skcipher().
>
> This bug is found by a static analysis tool STCheck written by us.
>
> Signed-off-by: Jia-Ju Bai <[email protected]>
> ---
> net/ceph/crypto.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/ceph/crypto.c b/net/ceph/crypto.c
> index 5d6724cee38f..ac28463bcfd8 100644
> --- a/net/ceph/crypto.c
> +++ b/net/ceph/crypto.c
> @@ -136,7 +136,8 @@ void ceph_crypto_key_destroy(struct ceph_crypto_key *key)
> if (key) {
> kfree(key->key);
> key->key = NULL;
> - crypto_free_sync_skcipher(key->tfm);
> + if (key->tfm)
> + crypto_free_sync_skcipher(key->tfm);
> key->tfm = NULL;
> }
> }

Hi Jia-Ju,

Yeah, looks like the only reason this continued to work after
69d6302b65a8 ("libceph: Remove VLA usage of skcipher") is because
crypto_sync_skcipher is a trivial wrapper around crypto_skcipher
added just for type checking AFAICT.

struct crypto_sync_skcipher {
struct crypto_skcipher base;
};

Before that ceph_crypto_key_destroy() used crypto_free_skcipher(),
which is safe to call on a NULL tfm.

Applied with a slight modification -- I moved key->tfm = NULL under
the new if and amended the changelog.

https://github.com/ceph/ceph-client/commit/b3d79916ff99074d289d66f1643b423ae0008c50

Thanks,

Ilya