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authorDavid Howells <dhowells@redhat.com>2017-10-04 16:43:25 +0100
committerDavid Howells <dhowells@redhat.com>2017-10-18 09:12:40 +0100
commit363b02dab09b3226f3bd1420dad9c72b79a42a76 (patch)
tree9162410e681bbbd73f951d5942aac5a95f568a6b /security/keys/keyctl.c
parentKEYS: checking the input id parameters before finding asymmetric key (diff)
downloadlinux-dev-363b02dab09b3226f3bd1420dad9c72b79a42a76.tar.xz
linux-dev-363b02dab09b3226f3bd1420dad9c72b79a42a76.zip
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 <ebiggers@google.com> Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Eric Biggers <ebiggers@google.com>
Diffstat (limited to 'security/keys/keyctl.c')
-rw-r--r--security/keys/keyctl.c9
1 files changed, 4 insertions, 5 deletions
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 365ff85d7e27..76d22f726ae4 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -766,10 +766,9 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)
key = key_ref_to_ptr(key_ref);
- if (test_bit(KEY_FLAG_NEGATIVE, &key->flags)) {
- ret = -ENOKEY;
- goto error2;
- }
+ ret = key_read_state(key);
+ if (ret < 0)
+ goto error2; /* Negatively instantiated */
/* see if we can read it directly */
ret = key_permission(key_ref, KEY_NEED_READ);
@@ -901,7 +900,7 @@ long keyctl_chown_key(key_serial_t id, uid_t user, gid_t group)
atomic_dec(&key->user->nkeys);
atomic_inc(&newowner->nkeys);
- if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags)) {
+ if (key->state != KEY_IS_UNINSTANTIATED) {
atomic_dec(&key->user->nikeys);
atomic_inc(&newowner->nikeys);
}