fs, nfs: convert nfs_client.cl_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 nfs_client.cl_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>

1 files changed, 6 insertions, 6 deletions

diff --git a/fs/nfs/filelayout/filelayout.c b/fs/nfs/filelayout/filelayout.c
index 508126eb49f9..4e54d8b5413a 100644
--- a/fs/nfs/filelayout/filelayout.c
+++ b/fs/nfs/filelayout/filelayout.c
@@ -471,10 +471,10 @@ filelayout_read_pagelist(struct nfs_pgio_header *hdr)
                 return PNFS_NOT_ATTEMPTED;
 
         dprintk("%s USE DS: %s cl_count %d\n", __func__,
-                ds->ds_remotestr, atomic_read(&ds->ds_clp->cl_count));
+                ds->ds_remotestr, refcount_read(&ds->ds_clp->cl_count));
 
         /* No multipath support. Use first DS */
-        atomic_inc(&ds->ds_clp->cl_count);
+        refcount_inc(&ds->ds_clp->cl_count);
         hdr->ds_clp = ds->ds_clp;
         hdr->ds_commit_idx = idx;
         fh = nfs4_fl_select_ds_fh(lseg, j);
@@ -515,10 +515,10 @@ filelayout_write_pagelist(struct nfs_pgio_header *hdr, int sync)
 
         dprintk("%s ino %lu sync %d req %zu@%llu DS: %s cl_count %d\n",
                 __func__, hdr->inode->i_ino, sync, (size_t) hdr->args.count,
-                offset, ds->ds_remotestr, atomic_read(&ds->ds_clp->cl_count));
+                offset, ds->ds_remotestr, refcount_read(&ds->ds_clp->cl_count));
 
         hdr->pgio_done_cb = filelayout_write_done_cb;
-        atomic_inc(&ds->ds_clp->cl_count);
+        refcount_inc(&ds->ds_clp->cl_count);
         hdr->ds_clp = ds->ds_clp;
         hdr->ds_commit_idx = idx;
         fh = nfs4_fl_select_ds_fh(lseg, j);
@@ -1064,9 +1064,9 @@ static int filelayout_initiate_commit(struct nfs_commit_data *data, int how)
                 goto out_err;
 
         dprintk("%s ino %lu, how %d cl_count %d\n", __func__,
-                data->inode->i_ino, how, atomic_read(&ds->ds_clp->cl_count));
+                data->inode->i_ino, how, refcount_read(&ds->ds_clp->cl_count));
         data->commit_done_cb = filelayout_commit_done_cb;
-        atomic_inc(&ds->ds_clp->cl_count);
+        refcount_inc(&ds->ds_clp->cl_count);
         data->ds_clp = ds->ds_clp;
         fh = select_ds_fh_from_commit(lseg, data->ds_commit_index);
         if (fh)