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fs, nfsd: convert nfs4_file.fi_ref 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 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>
This commit is contained in:
Elena Reshetova
2017-10-20 12:53:30 +03:00
committed by J. Bruce Fields
parent cff7cb2ece
commit 818a34eb26
2 changed files with 5 additions and 5 deletions
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4
fs/nfsd/state.h
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@@ -484,7 +484,7 @@ 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;
@@ -637,7 +637,7 @@ 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);