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fs, nfs: convert nfs_cache_defer_req.count from atomic_t to refcount_t

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atomic_t variables are currently used to implement reference
counters with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable nfs_cache_defer_req.count is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
This commit is contained in:
Elena Reshetova 2017-10-20 12:53:35 +03:00 committed by Anna Schumaker
parent 81a090b997
commit 0896cade12
2 changed files with 4 additions and 4 deletions
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6
fs/nfs/cache_lib.c
View file

@ -66,7 +66,7 @@ int nfs_cache_upcall(struct cache_detail *cd, char *entry_name)
*/
void nfs_cache_defer_req_put(struct nfs_cache_defer_req *dreq)
{
if (atomic_dec_and_test(&dreq->count))
if (refcount_dec_and_test(&dreq->count))
kfree(dreq);
}
@ -86,7 +86,7 @@ static struct cache_deferred_req *nfs_dns_cache_defer(struct cache_req *req)
dreq = container_of(req, struct nfs_cache_defer_req, req);
dreq->deferred_req.revisit = nfs_dns_cache_revisit;
atomic_inc(&dreq->count);
refcount_inc(&dreq->count);
return &dreq->deferred_req;
}
@ -98,7 +98,7 @@ struct nfs_cache_defer_req *nfs_cache_defer_req_alloc(void)
dreq = kzalloc(sizeof(*dreq), GFP_KERNEL);
if (dreq) {
init_completion(&dreq->completion);
atomic_set(&dreq->count, 1);
refcount_set(&dreq->count, 1);
dreq->req.defer = nfs_dns_cache_defer;
}
return dreq;

2
fs/nfs/cache_lib.h
View file

@ -15,7 +15,7 @@ struct nfs_cache_defer_req {
struct cache_req req;
struct cache_deferred_req deferred_req;
struct completion completion;
atomic_t count;
refcount_t count;
};
extern int nfs_cache_upcall(struct cache_detail *cd, char *entry_name);