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 nfs4_file.fi_ref is used as pure reference counter.
Convert it to refcount_t and fix up the operations.
Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: David Windsor <dwindsor@xxxxxxxxx>
Reviewed-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
---
fs/nfsd/nfs4state.c | 6 +++---
fs/nfsd/state.h | 4 ++--
2 files changed, 5 insertions(+), 5 deletions(-)
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index fb61d79..55a5f7d 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -359,7 +359,7 @@ put_nfs4_file(struct nfs4_file *fi)
{
might_lock(&state_lock);
- if (atomic_dec_and_lock(&fi->fi_ref, &state_lock)) {
+ if (refcount_dec_and_lock(&fi->fi_ref, &state_lock)) {
hlist_del_rcu(&fi->fi_hash);
spin_unlock(&state_lock);
WARN_ON_ONCE(!list_empty(&fi->fi_clnt_odstate));
@@ -3351,7 +3351,7 @@ static void nfsd4_init_file(struct knfsd_fh *fh, unsigned int hashval,
{
lockdep_assert_held(&state_lock);
- atomic_set(&fp->fi_ref, 1);
+ refcount_set(&fp->fi_ref, 1);
spin_lock_init(&fp->fi_lock);
INIT_LIST_HEAD(&fp->fi_stateids);
INIT_LIST_HEAD(&fp->fi_delegations);
@@ -3647,7 +3647,7 @@ find_file_locked(struct knfsd_fh *fh, unsigned int hashval)
hlist_for_each_entry_rcu(fp, &file_hashtbl[hashval], fi_hash) {
if (fh_match(&fp->fi_fhandle, fh)) {
- if (atomic_inc_not_zero(&fp->fi_ref))
+ if (refcount_inc_not_zero(&fp->fi_ref))
return fp;
}
}
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index 58eb5f4..4797429 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -482,7 +482,7 @@ struct nfs4_clnt_odstate {
* the global state_lock spinlock.
*/
struct nfs4_file {
- atomic_t fi_ref;
+ refcount_t fi_ref;
spinlock_t fi_lock;
struct hlist_node fi_hash; /* hash on fi_fhandle */
struct list_head fi_stateids;
@@ -635,7 +635,7 @@ struct nfs4_file *find_file(struct knfsd_fh *fh);
void put_nfs4_file(struct nfs4_file *fi);
static inline void get_nfs4_file(struct nfs4_file *fi)
{
- atomic_inc(&fi->fi_ref);
+ refcount_inc(&fi->fi_ref);
}
struct file *find_any_file(struct nfs4_file *f);
--
2.7.4
--
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