From 13923d0865ca96312197962522e88bc0aedccd74 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Mon, 9 Oct 2017 12:37:49 -0700 Subject: KEYS: encrypted: fix dereference of NULL user_key_payload A key of type "encrypted" references a "master key" which is used to encrypt and decrypt the encrypted key's payload. However, when we accessed the master key's payload, we failed to handle the case where the master key has been revoked, which sets the payload pointer to NULL. Note that request_key() *does* skip revoked keys, but there is still a window where the key can be revoked before we acquire its semaphore. Fix it by checking for a NULL payload, treating it like a key which was already revoked at the time it was requested. This was an issue for master keys of type "user" only. Master keys can also be of type "trusted", but those cannot be revoked. Fixes: 7e70cb497850 ("keys: add new key-type encrypted") Reviewed-by: James Morris Cc: [v2.6.38+] Cc: Mimi Zohar Cc: David Safford Signed-off-by: Eric Biggers Signed-off-by: David Howells --- security/keys/encrypted-keys/encrypted.c | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'security/keys/encrypted-keys/encrypted.c') diff --git a/security/keys/encrypted-keys/encrypted.c b/security/keys/encrypted-keys/encrypted.c index 69855ba0d3b3..535db141f4da 100644 --- a/security/keys/encrypted-keys/encrypted.c +++ b/security/keys/encrypted-keys/encrypted.c @@ -309,6 +309,13 @@ static struct key *request_user_key(const char *master_desc, const u8 **master_k down_read(&ukey->sem); upayload = user_key_payload_locked(ukey); + if (!upayload) { + /* key was revoked before we acquired its semaphore */ + up_read(&ukey->sem); + key_put(ukey); + ukey = ERR_PTR(-EKEYREVOKED); + goto error; + } *master_key = upayload->data; *master_keylen = upayload->datalen; error: -- cgit v1.2.3 From 363b02dab09b3226f3bd1420dad9c72b79a42a76 Mon Sep 17 00:00:00 2001 From: David Howells Date: Wed, 4 Oct 2017 16:43:25 +0100 Subject: KEYS: Fix race between updating and finding a negative key Consolidate KEY_FLAG_INSTANTIATED, KEY_FLAG_NEGATIVE and the rejection error into one field such that: (1) The instantiation state can be modified/read atomically. (2) The error can be accessed atomically with the state. (3) The error isn't stored unioned with the payload pointers. This deals with the problem that the state is spread over three different objects (two bits and a separate variable) and reading or updating them atomically isn't practical, given that not only can uninstantiated keys change into instantiated or rejected keys, but rejected keys can also turn into instantiated keys - and someone accessing the key might not be using any locking. The main side effect of this problem is that what was held in the payload may change, depending on the state. For instance, you might observe the key to be in the rejected state. You then read the cached error, but if the key semaphore wasn't locked, the key might've become instantiated between the two reads - and you might now have something in hand that isn't actually an error code. The state is now KEY_IS_UNINSTANTIATED, KEY_IS_POSITIVE or a negative error code if the key is negatively instantiated. The key_is_instantiated() function is replaced with key_is_positive() to avoid confusion as negative keys are also 'instantiated'. Additionally, barriering is included: (1) Order payload-set before state-set during instantiation. (2) Order state-read before payload-read when using the key. Further separate barriering is necessary if RCU is being used to access the payload content after reading the payload pointers. Fixes: 146aa8b1453b ("KEYS: Merge the type-specific data with the payload data") Cc: stable@vger.kernel.org # v4.4+ Reported-by: Eric Biggers Signed-off-by: David Howells Reviewed-by: Eric Biggers --- security/keys/encrypted-keys/encrypted.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'security/keys/encrypted-keys/encrypted.c') diff --git a/security/keys/encrypted-keys/encrypted.c b/security/keys/encrypted-keys/encrypted.c index 535db141f4da..d92cbf9687c3 100644 --- a/security/keys/encrypted-keys/encrypted.c +++ b/security/keys/encrypted-keys/encrypted.c @@ -854,7 +854,7 @@ static int encrypted_update(struct key *key, struct key_preparsed_payload *prep) size_t datalen = prep->datalen; int ret = 0; - if (test_bit(KEY_FLAG_NEGATIVE, &key->flags)) + if (key_is_negative(key)) return -ENOKEY; if (datalen <= 0 || datalen > 32767 || !prep->data) return -EINVAL; -- cgit v1.2.3