linux-kernel - Re: [PATCH] KEYS: Add missing smp_rmb() primitives to the keyring search code

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Date:	Tue, 17 Jan 2012 10:38:05 +1100 (EST)
From:	James Morris <jmorris@...ei.org>
To:	David Howells <dhowells@...hat.com>
cc:	keyrings@...ux-nfs.org, linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KEYS: Add missing smp_rmb() primitives to the keyring
 search code

On Mon, 16 Jan 2012, David Howells wrote:

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

Does this need to go into 3.3 and stable?


> 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@...hat.com>
> Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
> 
>  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)
> 

-- 
James Morris
<jmorris@...ei.org>
--
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