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fs, nfsd: convert nfs4_file.fi_ref from atomic_t to refcount_t
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@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: J. Bruce Fields <bfields@redhat.com>
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@ -359,7 +359,7 @@ put_nfs4_file(struct nfs4_file *fi)
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{
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might_lock(&state_lock);
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if (atomic_dec_and_lock(&fi->fi_ref, &state_lock)) {
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if (refcount_dec_and_lock(&fi->fi_ref, &state_lock)) {
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hlist_del_rcu(&fi->fi_hash);
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spin_unlock(&state_lock);
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WARN_ON_ONCE(!list_empty(&fi->fi_clnt_odstate));
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@ -3401,7 +3401,7 @@ static void nfsd4_init_file(struct knfsd_fh *fh, unsigned int hashval,
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{
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lockdep_assert_held(&state_lock);
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atomic_set(&fp->fi_ref, 1);
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refcount_set(&fp->fi_ref, 1);
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spin_lock_init(&fp->fi_lock);
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INIT_LIST_HEAD(&fp->fi_stateids);
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INIT_LIST_HEAD(&fp->fi_delegations);
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@ -3697,7 +3697,7 @@ find_file_locked(struct knfsd_fh *fh, unsigned int hashval)
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hlist_for_each_entry_rcu(fp, &file_hashtbl[hashval], fi_hash) {
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if (fh_match(&fp->fi_fhandle, fh)) {
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if (atomic_inc_not_zero(&fp->fi_ref))
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if (refcount_inc_not_zero(&fp->fi_ref))
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return fp;
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}
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}
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@ -484,7 +484,7 @@ struct nfs4_clnt_odstate {
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* the global state_lock spinlock.
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*/
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struct nfs4_file {
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atomic_t fi_ref;
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refcount_t fi_ref;
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spinlock_t fi_lock;
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struct hlist_node fi_hash; /* hash on fi_fhandle */
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struct list_head fi_stateids;
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@ -637,7 +637,7 @@ struct nfs4_file *find_file(struct knfsd_fh *fh);
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void put_nfs4_file(struct nfs4_file *fi);
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static inline void get_nfs4_file(struct nfs4_file *fi)
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{
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atomic_inc(&fi->fi_ref);
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refcount_inc(&fi->fi_ref);
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}
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struct file *find_any_file(struct nfs4_file *f);
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