[PATCH] KEYS: Add missing smp_rmb() primitives to the keyring searchcode

From: David Howells
Date: Mon Jan 16 2012 - 11:03:59 EST


Add missing smp_rmb() primitives to the keyring search code.

When keyring payloads are appended to without replacement (thus using up spare
slots in the key pointer array), an smp_wmb() is issued between the pointer
assignment and the increment of the key count (nkeys).

There should be corresponding read barriers between the read of nkeys and
dereferences of keys[n] when n is dependent on the value of nkeys.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---

security/keys/gc.c | 4 +++-
security/keys/keyring.c | 22 +++++++++++++++-------
2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/security/keys/gc.c b/security/keys/gc.c
index bf4d8da..a42b455 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -145,7 +145,9 @@ static void key_gc_keyring(struct key *keyring, time_t limit)
if (!klist)
goto unlock_dont_gc;

- for (loop = klist->nkeys - 1; loop >= 0; loop--) {
+ loop = klist->nkeys;
+ smp_rmb();
+ for (loop--; loop >= 0; loop--) {
key = klist->keys[loop];
if (test_bit(KEY_FLAG_DEAD, &key->flags) ||
(key->expiry > 0 && key->expiry <= limit))
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 37a7f3b..d605f75 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -319,7 +319,7 @@ key_ref_t keyring_search_aux(key_ref_t keyring_ref,
struct key *keyring, *key;
key_ref_t key_ref;
long err;
- int sp, kix;
+ int sp, nkeys, kix;

keyring = key_ref_to_ptr(keyring_ref);
possessed = is_key_possessed(keyring_ref);
@@ -380,7 +380,9 @@ descend:
goto not_this_keyring;

/* iterate through the keys in this keyring first */
- for (kix = 0; kix < keylist->nkeys; kix++) {
+ nkeys = keylist->nkeys;
+ smp_rmb();
+ for (kix = 0; kix < nkeys; kix++) {
key = keylist->keys[kix];
kflags = key->flags;

@@ -421,7 +423,9 @@ descend:
/* search through the keyrings nested in this one */
kix = 0;
ascend:
- for (; kix < keylist->nkeys; kix++) {
+ nkeys = keylist->nkeys;
+ smp_rmb();
+ for (; kix < nkeys; kix++) {
key = keylist->keys[kix];
if (key->type != &key_type_keyring)
continue;
@@ -515,7 +519,7 @@ key_ref_t __keyring_search_one(key_ref_t keyring_ref,
struct keyring_list *klist;
unsigned long possessed;
struct key *keyring, *key;
- int loop;
+ int nkeys, loop;

keyring = key_ref_to_ptr(keyring_ref);
possessed = is_key_possessed(keyring_ref);
@@ -524,7 +528,9 @@ key_ref_t __keyring_search_one(key_ref_t keyring_ref,

klist = rcu_dereference(keyring->payload.subscriptions);
if (klist) {
- for (loop = 0; loop < klist->nkeys; loop++) {
+ nkeys = klist->nkeys;
+ smp_rmb();
+ for (loop = 0; loop < nkeys ; loop++) {
key = klist->keys[loop];

if (key->type == ktype &&
@@ -622,7 +628,7 @@ static int keyring_detect_cycle(struct key *A, struct key *B)

struct keyring_list *keylist;
struct key *subtree, *key;
- int sp, kix, ret;
+ int sp, nkeys, kix, ret;

rcu_read_lock();

@@ -645,7 +651,9 @@ descend:

ascend:
/* iterate through the remaining keys in this keyring */
- for (; kix < keylist->nkeys; kix++) {
+ nkeys = keylist->nkeys;
+ smp_rmb();
+ for (; kix < nkeys; kix++) {
key = keylist->keys[kix];

if (key == A)

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