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 <[email protected]> Reviewed-by: David Windsor <[email protected]> Reviewed-by: Hans Liljestrand <[email protected]> Signed-off-by: Elena Reshetova <[email protected]> --- fs/nfs/cache_lib.c | 6 +++--- fs/nfs/cache_lib.h | 2 +- 2 files changed, 4 insertions(+), 4 deletions(-) diff --git a/fs/nfs/cache_lib.c b/fs/nfs/cache_lib.c index 2ae676f..6167f13 100644 --- a/fs/nfs/cache_lib.c +++ b/fs/nfs/cache_lib.c @@ -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; diff --git a/fs/nfs/cache_lib.h b/fs/nfs/cache_lib.h index 4116d2c..02b378c 100644 --- a/fs/nfs/cache_lib.h +++ b/fs/nfs/cache_lib.h @@ -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); -- 2.7.4
