fs, nfs: convert nfs4_pnfs_ds.ds_count 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_pnfs_ds.ds_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>

diff --git a/fs/nfs/pnfs.h b/fs/nfs/pnfs.h
index 87f144f14d1e0c0c6c3232cc54c6e6b4167d5c24..cefa7daf6e85e52e3c84ebd94e2265bc976dc119 100644 (file)
--- a/fs/nfs/pnfs.h
+++ b/fs/nfs/pnfs.h
@@ -30,6 +30,7 @@
 #ifndef FS_NFS_PNFS_H
 #define FS_NFS_PNFS_H
 
+#include <linux/refcount.h>
 #include <linux/nfs_fs.h>
 #include <linux/nfs_page.h>
 #include <linux/workqueue.h>
@@ -54,7 +55,7 @@ struct nfs4_pnfs_ds {
        char                    *ds_remotestr;  /* comma sep list of addrs */
        struct list_head        ds_addrs;
        struct nfs_client       *ds_clp;
-       atomic_t                ds_count;
+       refcount_t              ds_count;
        unsigned long           ds_state;
 #define NFS4DS_CONNECTING      0       /* ds is establishing connection */
 };

diff --git a/fs/nfs/pnfs_nfs.c b/fs/nfs/pnfs_nfs.c
index 60da59be83b6128241bf3be4a93e153e0329421a..03aaa60c7768a087ed99bd381fa299161dc9716d 100644 (file)
--- a/fs/nfs/pnfs_nfs.c
+++ b/fs/nfs/pnfs_nfs.c
@@ -338,7 +338,7 @@ print_ds(struct nfs4_pnfs_ds *ds)
                "        client %p\n"
                "        cl_exchange_flags %x\n",
                ds->ds_remotestr,
-               atomic_read(&ds->ds_count), ds->ds_clp,
+               refcount_read(&ds->ds_count), ds->ds_clp,
                ds->ds_clp ? ds->ds_clp->cl_exchange_flags : 0);
 }
 
@@ -451,7 +451,7 @@ static void destroy_ds(struct nfs4_pnfs_ds *ds)
 
 void nfs4_pnfs_ds_put(struct nfs4_pnfs_ds *ds)
 {
-       if (atomic_dec_and_lock(&ds->ds_count,
+       if (refcount_dec_and_lock(&ds->ds_count,
                                &nfs4_ds_cache_lock)) {
                list_del_init(&ds->ds_node);
                spin_unlock(&nfs4_ds_cache_lock);
@@ -537,7 +537,7 @@ nfs4_pnfs_ds_add(struct list_head *dsaddrs, gfp_t gfp_flags)
                INIT_LIST_HEAD(&ds->ds_addrs);
                list_splice_init(dsaddrs, &ds->ds_addrs);
                ds->ds_remotestr = remotestr;
-               atomic_set(&ds->ds_count, 1);
+               refcount_set(&ds->ds_count, 1);
                INIT_LIST_HEAD(&ds->ds_node);
                ds->ds_clp = NULL;
                list_add(&ds->ds_node, &nfs4_data_server_cache);
@@ -546,10 +546,10 @@ nfs4_pnfs_ds_add(struct list_head *dsaddrs, gfp_t gfp_flags)
        } else {
                kfree(remotestr);
                kfree(ds);
-               atomic_inc(&tmp_ds->ds_count);
+               refcount_inc(&tmp_ds->ds_count);
                dprintk("%s data server %s found, inc'ed ds_count to %d\n",
                        __func__, tmp_ds->ds_remotestr,
-                       atomic_read(&tmp_ds->ds_count));
+                       refcount_read(&tmp_ds->ds_count));
                ds = tmp_ds;
        }
        spin_unlock(&nfs4_ds_cache_lock);