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SubjectRe: [PATCH] SMACK: Add missing rcu_read_lock/unlock for process capability walk.
On 4/20/2011 3:00 PM, Andi Kleen wrote:
> From: Andi Kleen <ak@linux.intel.com>
>
> smk_access_entry does a RCU list walk for a list shared with other
> threads. It relies on the caller doing rcu_read_lock().
> One caller forgot to do to this, which could lead to races
> on preemptible kernels.
>
> Move the rcu_read_lock() into smk_access_entry instead.

Nacked-by: Casey Schaufler <casey@schaufler-ca.com>

The lock was moved out of smk_access_entry in support of the
processing done in the smack_mmap_file() hook. Where do you see
a potential race, and which caller "forgot" to do the lock?

Thank you.

> Signed-off-by: Andi Kleen <ak@linux.intel.com>
> ---
> security/smack/smack_access.c | 4 ++--
> 1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
> index 7b0d3b3..43b20f3 100644
> --- a/security/smack/smack_access.c
> +++ b/security/smack/smack_access.c
> @@ -92,6 +92,7 @@ int smk_access_entry(char *subject_label, char *object_label,
> int may = -ENOENT;
> struct smack_rule *srp;
>
> + rcu_read_lock();
> list_for_each_entry_rcu(srp, rule_list, list) {
> if (srp->smk_subject == subject_label ||
> strcmp(srp->smk_subject, subject_label) == 0) {
> @@ -102,6 +103,7 @@ int smk_access_entry(char *subject_label, char *object_label,
> }
> }
> }
> + rcu_read_unlock();
>
> return may;
> }
> @@ -184,9 +186,7 @@ int smk_access_flags(char *subject_label, char *object_label, int request,
> * good. A negative response from smk_access_entry()
> * indicates there is no entry for this pair.
> */
> - rcu_read_lock();
> may = smk_access_entry(subject_label, object_label, &smack_rule_list);
> - rcu_read_unlock();
>
> if (may > 0 && (request & may) == request)
> goto out_audit;



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