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Subject[PATCH 06/10] keys: Hoist locking out of __key_link_begin() [ver #3]
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Hoist the locking of out of __key_link_begin() and into its callers.  This
is necessary to allow the upcoming key_move() operation to correctly order
taking of the source keyring semaphore, the destination keyring semaphore
and the keyring serialisation lock.

Signed-off-by: David Howells <dhowells@redhat.com>
---

security/keys/internal.h | 2 +
security/keys/key.c | 27 ++++++++++++---
security/keys/keyring.c | 78 ++++++++++++++++++++++++++-----------------
security/keys/request_key.c | 7 +++-
4 files changed, 76 insertions(+), 38 deletions(-)

diff --git a/security/keys/internal.h b/security/keys/internal.h
index 8f533c81aa8d..25cdd0cbdc06 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -93,6 +93,8 @@ extern wait_queue_head_t request_key_conswq;
extern struct key_type *key_type_lookup(const char *type);
extern void key_type_put(struct key_type *ktype);

+extern int __key_link_lock(struct key *keyring,
+ const struct keyring_index_key *index_key);
extern int __key_link_begin(struct key *keyring,
const struct keyring_index_key *index_key,
struct assoc_array_edit **_edit);
diff --git a/security/keys/key.c b/security/keys/key.c
index 696f1c092c50..bba71acec886 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -500,7 +500,7 @@ int key_instantiate_and_link(struct key *key,
struct key *authkey)
{
struct key_preparsed_payload prep;
- struct assoc_array_edit *edit;
+ struct assoc_array_edit *edit = NULL;
int ret;

memset(&prep, 0, sizeof(prep));
@@ -515,10 +515,14 @@ int key_instantiate_and_link(struct key *key,
}

if (keyring) {
- ret = __key_link_begin(keyring, &key->index_key, &edit);
+ ret = __key_link_lock(keyring, &key->index_key);
if (ret < 0)
goto error;

+ ret = __key_link_begin(keyring, &key->index_key, &edit);
+ if (ret < 0)
+ goto error_link_end;
+
if (keyring->restrict_link && keyring->restrict_link->check) {
struct key_restriction *keyres = keyring->restrict_link;

@@ -570,7 +574,7 @@ int key_reject_and_link(struct key *key,
struct key *keyring,
struct key *authkey)
{
- struct assoc_array_edit *edit;
+ struct assoc_array_edit *edit = NULL;
int ret, awaken, link_ret = 0;

key_check(key);
@@ -583,7 +587,12 @@ int key_reject_and_link(struct key *key,
if (keyring->restrict_link)
return -EPERM;

- link_ret = __key_link_begin(keyring, &key->index_key, &edit);
+ link_ret = __key_link_lock(keyring, &key->index_key);
+ if (link_ret == 0) {
+ link_ret = __key_link_begin(keyring, &key->index_key, &edit);
+ if (link_ret < 0)
+ __key_link_end(keyring, &key->index_key, edit);
+ }
}

mutex_lock(&key_construction_mutex);
@@ -810,7 +819,7 @@ key_ref_t key_create_or_update(key_ref_t keyring_ref,
.description = description,
};
struct key_preparsed_payload prep;
- struct assoc_array_edit *edit;
+ struct assoc_array_edit *edit = NULL;
const struct cred *cred = current_cred();
struct key *keyring, *key = NULL;
key_ref_t key_ref;
@@ -860,12 +869,18 @@ key_ref_t key_create_or_update(key_ref_t keyring_ref,
}
index_key.desc_len = strlen(index_key.description);

- ret = __key_link_begin(keyring, &index_key, &edit);
+ ret = __key_link_lock(keyring, &index_key);
if (ret < 0) {
key_ref = ERR_PTR(ret);
goto error_free_prep;
}

+ ret = __key_link_begin(keyring, &index_key, &edit);
+ if (ret < 0) {
+ key_ref = ERR_PTR(ret);
+ goto error_link_end;
+ }
+
if (restrict_link && restrict_link->check) {
ret = restrict_link->check(keyring, index_key.type,
&prep.payload, restrict_link->key);
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 6990c7761eaa..12acad3db6cf 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -1199,14 +1199,34 @@ static int keyring_detect_cycle(struct key *A, struct key *B)
return PTR_ERR(ctx.result) == -EAGAIN ? 0 : PTR_ERR(ctx.result);
}

+/*
+ * Lock keyring for link.
+ */
+int __key_link_lock(struct key *keyring,
+ const struct keyring_index_key *index_key)
+ __acquires(&keyring->sem)
+ __acquires(&keyring_serialise_link_lock)
+{
+ if (keyring->type != &key_type_keyring)
+ return -ENOTDIR;
+
+ down_write(&keyring->sem);
+
+ /* Serialise link/link calls to prevent parallel calls causing a cycle
+ * when linking two keyring in opposite orders.
+ */
+ if (index_key->type == &key_type_keyring)
+ mutex_lock(&keyring_serialise_link_lock);
+
+ return 0;
+}
+
/*
* Preallocate memory so that a key can be linked into to a keyring.
*/
int __key_link_begin(struct key *keyring,
const struct keyring_index_key *index_key,
struct assoc_array_edit **_edit)
- __acquires(&keyring->sem)
- __acquires(&keyring_serialise_link_lock)
{
struct assoc_array_edit *edit;
int ret;
@@ -1215,20 +1235,13 @@ int __key_link_begin(struct key *keyring,
keyring->serial, index_key->type->name, index_key->description);

BUG_ON(index_key->desc_len == 0);
+ BUG_ON(*_edit != NULL);

- if (keyring->type != &key_type_keyring)
- return -ENOTDIR;
-
- down_write(&keyring->sem);
+ *_edit = NULL;

ret = -EKEYREVOKED;
if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
- goto error_krsem;
-
- /* serialise link/link calls to prevent parallel calls causing a cycle
- * when linking two keyring in opposite orders */
- if (index_key->type == &key_type_keyring)
- mutex_lock(&keyring_serialise_link_lock);
+ goto error;

/* Create an edit script that will insert/replace the key in the
* keyring tree.
@@ -1239,7 +1252,7 @@ int __key_link_begin(struct key *keyring,
NULL);
if (IS_ERR(edit)) {
ret = PTR_ERR(edit);
- goto error_sem;
+ goto error;
}

/* If we're not replacing a link in-place then we're going to need some
@@ -1258,11 +1271,7 @@ int __key_link_begin(struct key *keyring,

error_cancel:
assoc_array_cancel_edit(edit);
-error_sem:
- if (index_key->type == &key_type_keyring)
- mutex_unlock(&keyring_serialise_link_lock);
-error_krsem:
- up_write(&keyring->sem);
+error:
kleave(" = %d", ret);
return ret;
}
@@ -1312,9 +1321,6 @@ void __key_link_end(struct key *keyring,
BUG_ON(index_key->type == NULL);
kenter("%d,%s,", keyring->serial, index_key->type->name);

- if (index_key->type == &key_type_keyring)
- mutex_unlock(&keyring_serialise_link_lock);
-
if (edit) {
if (!edit->dead_leaf) {
key_payload_reserve(keyring,
@@ -1323,6 +1329,9 @@ void __key_link_end(struct key *keyring,
assoc_array_cancel_edit(edit);
}
up_write(&keyring->sem);
+
+ if (index_key->type == &key_type_keyring)
+ mutex_unlock(&keyring_serialise_link_lock);
}

/*
@@ -1358,7 +1367,7 @@ static int __key_link_check_restriction(struct key *keyring, struct key *key)
*/
int key_link(struct key *keyring, struct key *key)
{
- struct assoc_array_edit *edit;
+ struct assoc_array_edit *edit = NULL;
int ret;

kenter("{%d,%d}", keyring->serial, refcount_read(&keyring->usage));
@@ -1366,17 +1375,24 @@ int key_link(struct key *keyring, struct key *key)
key_check(keyring);
key_check(key);

+ ret = __key_link_lock(keyring, &key->index_key);
+ if (ret < 0)
+ goto error;
+
ret = __key_link_begin(keyring, &key->index_key, &edit);
- if (ret == 0) {
- kdebug("begun {%d,%d}", keyring->serial, refcount_read(&keyring->usage));
- ret = __key_link_check_restriction(keyring, key);
- if (ret == 0)
- ret = __key_link_check_live_key(keyring, key);
- if (ret == 0)
- __key_link(key, &edit);
- __key_link_end(keyring, &key->index_key, edit);
- }
+ if (ret < 0)
+ goto error_end;
+
+ kdebug("begun {%d,%d}", keyring->serial, refcount_read(&keyring->usage));
+ ret = __key_link_check_restriction(keyring, key);
+ if (ret == 0)
+ ret = __key_link_check_live_key(keyring, key);
+ if (ret == 0)
+ __key_link(key, &edit);

+error_end:
+ __key_link_end(keyring, &key->index_key, edit);
+error:
kleave(" = %d {%d,%d}", ret, keyring->serial, refcount_read(&keyring->usage));
return ret;
}
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 1f234b019437..857da65e1940 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -343,7 +343,7 @@ static int construct_alloc_key(struct keyring_search_context *ctx,
struct key_user *user,
struct key **_key)
{
- struct assoc_array_edit *edit;
+ struct assoc_array_edit *edit = NULL;
struct key *key;
key_perm_t perm;
key_ref_t key_ref;
@@ -372,6 +372,9 @@ static int construct_alloc_key(struct keyring_search_context *ctx,
set_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);

if (dest_keyring) {
+ ret = __key_link_lock(dest_keyring, &ctx->index_key);
+ if (ret < 0)
+ goto link_lock_failed;
ret = __key_link_begin(dest_keyring, &ctx->index_key, &edit);
if (ret < 0)
goto link_prealloc_failed;
@@ -423,6 +426,8 @@ static int construct_alloc_key(struct keyring_search_context *ctx,
return ret;

link_prealloc_failed:
+ __key_link_end(dest_keyring, &ctx->index_key, edit);
+link_lock_failed:
mutex_unlock(&user->cons_lock);
key_put(key);
kleave(" = %d [prelink]", ret);
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