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>

diff --git a/include/linux/key.h b/include/linux/key.h
index e315e16b6ff8a0aaade2552ee404d35e27da5570..8a15cabe928d0ee282742f0c44be26e7af01851d 100644 (file)
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -138,6 +138,11 @@ struct key_restriction {
        struct key_type *keytype;
 };
 
+enum key_state {
+       KEY_IS_UNINSTANTIATED,
+       KEY_IS_POSITIVE,                /* Positively instantiated */
+};
+
 /*****************************************************************************/
 /*
  * authentication token / access credential / keyring
@@ -169,6 +174,7 @@ struct key {
                                                 * - may not match RCU dereferenced payload
                                                 * - payload should contain own length
                                                 */
+       short                   state;          /* Key state (+) or rejection error (-) */
 
 #ifdef KEY_DEBUGGING
        unsigned                magic;
@@ -176,18 +182,16 @@ struct key {
 #endif
 
        unsigned long           flags;          /* status flags (change with bitops) */
-#define KEY_FLAG_INSTANTIATED  0       /* set if key has been instantiated */
-#define KEY_FLAG_DEAD          1       /* set if key type has been deleted */
-#define KEY_FLAG_REVOKED       2       /* set if key had been revoked */
-#define KEY_FLAG_IN_QUOTA      3       /* set if key consumes quota */
-#define KEY_FLAG_USER_CONSTRUCT        4       /* set if key is being constructed in userspace */
-#define KEY_FLAG_NEGATIVE      5       /* set if key is negative */
-#define KEY_FLAG_ROOT_CAN_CLEAR        6       /* set if key can be cleared by root without permission */
-#define KEY_FLAG_INVALIDATED   7       /* set if key has been invalidated */
-#define KEY_FLAG_BUILTIN       8       /* set if key is built in to the kernel */
-#define KEY_FLAG_ROOT_CAN_INVAL        9       /* set if key can be invalidated by root without permission */
-#define KEY_FLAG_KEEP          10      /* set if key should not be removed */
-#define KEY_FLAG_UID_KEYRING   11      /* set if key is a user or user session keyring */
+#define KEY_FLAG_DEAD          0       /* set if key type has been deleted */
+#define KEY_FLAG_REVOKED       1       /* set if key had been revoked */
+#define KEY_FLAG_IN_QUOTA      2       /* set if key consumes quota */
+#define KEY_FLAG_USER_CONSTRUCT        3       /* set if key is being constructed in userspace */
+#define KEY_FLAG_ROOT_CAN_CLEAR        4       /* set if key can be cleared by root without permission */
+#define KEY_FLAG_INVALIDATED   5       /* set if key has been invalidated */
+#define KEY_FLAG_BUILTIN       6       /* set if key is built in to the kernel */
+#define KEY_FLAG_ROOT_CAN_INVAL        7       /* set if key can be invalidated by root without permission */
+#define KEY_FLAG_KEEP          8       /* set if key should not be removed */
+#define KEY_FLAG_UID_KEYRING   9       /* set if key is a user or user session keyring */
 
        /* the key type and key description string
         * - the desc is used to match a key against search criteria
@@ -213,7 +217,6 @@ struct key {
                        struct list_head name_link;
                        struct assoc_array keys;
                };
-               int reject_error;
        };
 
        /* This is set on a keyring to restrict the addition of a link to a key
@@ -353,17 +356,27 @@ extern void key_set_timeout(struct key *, unsigned);
 #define        KEY_NEED_SETATTR 0x20   /* Require permission to change attributes */
 #define        KEY_NEED_ALL    0x3f    /* All the above permissions */
 
+static inline short key_read_state(const struct key *key)
+{
+       /* Barrier versus mark_key_instantiated(). */
+       return smp_load_acquire(&key->state);
+}
+
 /**
- * key_is_instantiated - Determine if a key has been positively instantiated
+ * key_is_positive - Determine if a key has been positively instantiated
  * @key: The key to check.
  *
  * Return true if the specified key has been positively instantiated, false
  * otherwise.
  */
-static inline bool key_is_instantiated(const struct key *key)
+static inline bool key_is_positive(const struct key *key)
+{
+       return key_read_state(key) == KEY_IS_POSITIVE;
+}
+
+static inline bool key_is_negative(const struct key *key)
 {
-       return test_bit(KEY_FLAG_INSTANTIATED, &key->flags) &&
-               !test_bit(KEY_FLAG_NEGATIVE, &key->flags);
+       return key_read_state(key) < 0;
 }
 
 #define dereference_key_rcu(KEY)                                       \

diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c
index 8737412c7b27f33125c14c8aa6e64c4ce5cd2dc8..e1d4d898a007df9ba0911fd612caac4a48a50dc2 100644 (file)
--- a/net/dns_resolver/dns_key.c
+++ b/net/dns_resolver/dns_key.c
@@ -224,7 +224,7 @@ static int dns_resolver_match_preparse(struct key_match_data *match_data)
 static void dns_resolver_describe(const struct key *key, struct seq_file *m)
 {
        seq_puts(m, key->description);
-       if (key_is_instantiated(key)) {
+       if (key_is_positive(key)) {
                int err = PTR_ERR(key->payload.data[dns_key_error]);
 
                if (err)

diff --git a/security/keys/big_key.c b/security/keys/big_key.c
index e607830b6154ce4c8dbcd5563fb0d3607f680c8f..929e14978c421b227e592e937d9157ca2235b2f7 100644 (file)
--- a/security/keys/big_key.c
+++ b/security/keys/big_key.c
@@ -247,7 +247,7 @@ void big_key_revoke(struct key *key)
 
        /* clear the quota */
        key_payload_reserve(key, 0);
-       if (key_is_instantiated(key) &&
+       if (key_is_positive(key) &&
            (size_t)key->payload.data[big_key_len] > BIG_KEY_FILE_THRESHOLD)
                vfs_truncate(path, 0);
 }
@@ -279,7 +279,7 @@ void big_key_describe(const struct key *key, struct seq_file *m)
 
        seq_puts(m, key->description);
 
-       if (key_is_instantiated(key))
+       if (key_is_positive(key))
                seq_printf(m, ": %zu [%s]",
                           datalen,
                           datalen > BIG_KEY_FILE_THRESHOLD ? "file" : "buff");

diff --git a/security/keys/encrypted-keys/encrypted.c b/security/keys/encrypted-keys/encrypted.c
index 535db141f4da565dab213749aa039d656ca3846b..d92cbf9687c33f090865f6d0caa99d9936f49e3a 100644 (file)
--- 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;

diff --git a/security/keys/gc.c b/security/keys/gc.c
index 87cb260e4890f3ac464e8d3f3244077653510b74..f01d48cb3de1aac09266b59bcfa732597c6534b4 100644 (file)
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -129,15 +129,15 @@ static noinline void key_gc_unused_keys(struct list_head *keys)
        while (!list_empty(keys)) {
                struct key *key =
                        list_entry(keys->next, struct key, graveyard_link);
+               short state = key->state;
+
                list_del(&key->graveyard_link);
 
                kdebug("- %u", key->serial);
                key_check(key);
 
                /* Throw away the key data if the key is instantiated */
-               if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags) &&
-                   !test_bit(KEY_FLAG_NEGATIVE, &key->flags) &&
-                   key->type->destroy)
+               if (state == KEY_IS_POSITIVE && key->type->destroy)
                        key->type->destroy(key);
 
                security_key_free(key);
@@ -151,7 +151,7 @@ static noinline void key_gc_unused_keys(struct list_head *keys)
                }
 
                atomic_dec(&key->user->nkeys);
-               if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
+               if (state != KEY_IS_UNINSTANTIATED)
                        atomic_dec(&key->user->nikeys);
 
                key_user_put(key->user);

diff --git a/security/keys/key.c b/security/keys/key.c
index eb914a838840df416f26af2c0cd73f87c60a5032..9385e7cc710f8949145b65267028477e97c61d30 100644 (file)
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -401,6 +401,18 @@ int key_payload_reserve(struct key *key, size_t datalen)
 }
 EXPORT_SYMBOL(key_payload_reserve);
 
+/*
+ * Change the key state to being instantiated.
+ */
+static void mark_key_instantiated(struct key *key, int reject_error)
+{
+       /* Commit the payload before setting the state; barrier versus
+        * key_read_state().
+        */
+       smp_store_release(&key->state,
+                         (reject_error < 0) ? reject_error : KEY_IS_POSITIVE);
+}
+
 /*
  * Instantiate a key and link it into the target keyring atomically.  Must be
  * called with the target keyring's semaphore writelocked.  The target key's
@@ -424,14 +436,14 @@ static int __key_instantiate_and_link(struct key *key,
        mutex_lock(&key_construction_mutex);
 
        /* can't instantiate twice */
-       if (!test_bit(KEY_FLAG_INSTANTIATED, &key->flags)) {
+       if (key->state == KEY_IS_UNINSTANTIATED) {
                /* instantiate the key */
                ret = key->type->instantiate(key, prep);
 
                if (ret == 0) {
                        /* mark the key as being instantiated */
                        atomic_inc(&key->user->nikeys);
-                       set_bit(KEY_FLAG_INSTANTIATED, &key->flags);
+                       mark_key_instantiated(key, 0);
 
                        if (test_and_clear_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags))
                                awaken = 1;
@@ -577,13 +589,10 @@ int key_reject_and_link(struct key *key,
        mutex_lock(&key_construction_mutex);
 
        /* can't instantiate twice */
-       if (!test_bit(KEY_FLAG_INSTANTIATED, &key->flags)) {
+       if (key->state == KEY_IS_UNINSTANTIATED) {
                /* mark the key as being negatively instantiated */
                atomic_inc(&key->user->nikeys);
-               key->reject_error = -error;
-               smp_wmb();
-               set_bit(KEY_FLAG_NEGATIVE, &key->flags);
-               set_bit(KEY_FLAG_INSTANTIATED, &key->flags);
+               mark_key_instantiated(key, -error);
                now = current_kernel_time();
                key->expiry = now.tv_sec + timeout;
                key_schedule_gc(key->expiry + key_gc_delay);
@@ -752,8 +761,8 @@ static inline key_ref_t __key_update(key_ref_t key_ref,
 
        ret = key->type->update(key, prep);
        if (ret == 0)
-               /* updating a negative key instantiates it */
-               clear_bit(KEY_FLAG_NEGATIVE, &key->flags);
+               /* Updating a negative key positively instantiates it */
+               mark_key_instantiated(key, 0);
 
        up_write(&key->sem);
 
@@ -986,8 +995,8 @@ int key_update(key_ref_t key_ref, const void *payload, size_t plen)
 
        ret = key->type->update(key, &prep);
        if (ret == 0)
-               /* updating a negative key instantiates it */
-               clear_bit(KEY_FLAG_NEGATIVE, &key->flags);
+               /* Updating a negative key positively instantiates it */
+               mark_key_instantiated(key, 0);
 
        up_write(&key->sem);
 

diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 365ff85d7e27122db220fad6d633f8e0b352209f..76d22f726ae49d7e112c648c59e9c0d3124063f1 100644 (file)
--- 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);
                }

diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 4fa82a8a9c0e6cb778a08874724ea546cd602ade..06173b091a7481934d80e76cc3d55d00d01cb074 100644 (file)
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -414,7 +414,7 @@ static void keyring_describe(const struct key *keyring, struct seq_file *m)
        else
                seq_puts(m, "[anon]");
 
-       if (key_is_instantiated(keyring)) {
+       if (key_is_positive(keyring)) {
                if (keyring->keys.nr_leaves_on_tree != 0)
                        seq_printf(m, ": %lu", keyring->keys.nr_leaves_on_tree);
                else
@@ -553,7 +553,8 @@ static int keyring_search_iterator(const void *object, void *iterator_data)
 {
        struct keyring_search_context *ctx = iterator_data;
        const struct key *key = keyring_ptr_to_key(object);
-       unsigned long kflags = key->flags;
+       unsigned long kflags = READ_ONCE(key->flags);
+       short state = READ_ONCE(key->state);
 
        kenter("{%d}", key->serial);
 
@@ -597,9 +598,8 @@ static int keyring_search_iterator(const void *object, void *iterator_data)
 
        if (ctx->flags & KEYRING_SEARCH_DO_STATE_CHECK) {
                /* we set a different error code if we pass a negative key */
-               if (kflags & (1 << KEY_FLAG_NEGATIVE)) {
-                       smp_rmb();
-                       ctx->result = ERR_PTR(key->reject_error);
+               if (state < 0) {
+                       ctx->result = ERR_PTR(state);
                        kleave(" = %d [neg]", ctx->skipped_ret);
                        goto skipped;
                }

diff --git a/security/keys/proc.c b/security/keys/proc.c
index de834309d100206bedca18c84493af6fdb665d7a..4089ce1f7757d3590eebbe365a1a932bfe8bd25d 100644 (file)
--- a/security/keys/proc.c
+++ b/security/keys/proc.c
@@ -182,6 +182,7 @@ static int proc_keys_show(struct seq_file *m, void *v)
        unsigned long timo;
        key_ref_t key_ref, skey_ref;
        char xbuf[16];
+       short state;
        int rc;
 
        struct keyring_search_context ctx = {
@@ -236,17 +237,19 @@ static int proc_keys_show(struct seq_file *m, void *v)
                        sprintf(xbuf, "%luw", timo / (60*60*24*7));
        }
 
+       state = key_read_state(key);
+
 #define showflag(KEY, LETTER, FLAG) \
        (test_bit(FLAG, &(KEY)->flags) ? LETTER : '-')
 
        seq_printf(m, "%08x %c%c%c%c%c%c%c %5d %4s %08x %5d %5d %-9.9s ",
                   key->serial,
-                  showflag(key, 'I', KEY_FLAG_INSTANTIATED),
+                  state != KEY_IS_UNINSTANTIATED ? 'I' : '-',
                   showflag(key, 'R', KEY_FLAG_REVOKED),
                   showflag(key, 'D', KEY_FLAG_DEAD),
                   showflag(key, 'Q', KEY_FLAG_IN_QUOTA),
                   showflag(key, 'U', KEY_FLAG_USER_CONSTRUCT),
-                  showflag(key, 'N', KEY_FLAG_NEGATIVE),
+                  state < 0 ? 'N' : '-',
                   showflag(key, 'i', KEY_FLAG_INVALIDATED),
                   refcount_read(&key->usage),
                   xbuf,

diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index 293d3598153bf0c8611f319f4c1d7c50f364e600..740affd65ee98464e19fc32f830f86a1ad3f24f4 100644 (file)
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -730,7 +730,7 @@ try_again:
 
        ret = -EIO;
        if (!(lflags & KEY_LOOKUP_PARTIAL) &&
-           !test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
+           key_read_state(key) == KEY_IS_UNINSTANTIATED)
                goto invalid_key;
 
        /* check the permissions */

diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 63e63a42db3c0aa4b1ed069e03e8e1f8e9139a32..e8036cd0ad5430a87ec2e2ea1496e921ae941b3d 100644 (file)
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -595,10 +595,9 @@ int wait_for_key_construction(struct key *key, bool intr)
                          intr ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE);
        if (ret)
                return -ERESTARTSYS;
-       if (test_bit(KEY_FLAG_NEGATIVE, &key->flags)) {
-               smp_rmb();
-               return key->reject_error;
-       }
+       ret = key_read_state(key);
+       if (ret < 0)
+               return ret;
        return key_validate(key);
 }
 EXPORT_SYMBOL(wait_for_key_construction);

diff --git a/security/keys/request_key_auth.c b/security/keys/request_key_auth.c
index 6ebf1af8fce963eeb0cc4c423c153318096e65a6..424e1d90412ea0c40e4e20453f47b566b0b25834 100644 (file)
--- a/security/keys/request_key_auth.c
+++ b/security/keys/request_key_auth.c
@@ -73,7 +73,7 @@ static void request_key_auth_describe(const struct key *key,
 
        seq_puts(m, "key:");
        seq_puts(m, key->description);
-       if (key_is_instantiated(key))
+       if (key_is_positive(key))
                seq_printf(m, " pid:%d ci:%zu", rka->pid, rka->callout_len);
 }
 

diff --git a/security/keys/trusted.c b/security/keys/trusted.c
index ddfaebf60fc8649cf6159d2cba18e916931a3b4e..bd85315cbfeb3e1bad3b01e7d9a6538bbb5d3577 100644 (file)
--- a/security/keys/trusted.c
+++ b/security/keys/trusted.c
@@ -1066,7 +1066,7 @@ static int trusted_update(struct key *key, struct key_preparsed_payload *prep)
        char *datablob;
        int ret = 0;
 
-       if (test_bit(KEY_FLAG_NEGATIVE, &key->flags))
+       if (key_is_negative(key))
                return -ENOKEY;
        p = key->payload.data[0];
        if (!p->migratable)

diff --git a/security/keys/user_defined.c b/security/keys/user_defined.c
index 3d8c68eba5160286fa7af79c8da1ead6e6b05236..9f558bedba23a338da5980ab11dd1b716c7b0b67 100644 (file)
--- a/security/keys/user_defined.c
+++ b/security/keys/user_defined.c
@@ -114,7 +114,7 @@ int user_update(struct key *key, struct key_preparsed_payload *prep)
 
        /* attach the new data, displacing the old */
        key->expiry = prep->expiry;
-       if (!test_bit(KEY_FLAG_NEGATIVE, &key->flags))
+       if (key_is_positive(key))
                zap = dereference_key_locked(key);
        rcu_assign_keypointer(key, prep->payload.data[0]);
        prep->payload.data[0] = NULL;
@@ -162,7 +162,7 @@ EXPORT_SYMBOL_GPL(user_destroy);
 void user_describe(const struct key *key, struct seq_file *m)
 {
        seq_puts(m, key->description);
-       if (key_is_instantiated(key))
+       if (key_is_positive(key))
                seq_printf(m, ": %u", key->datalen);
 }