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fs, nfs: convert nfs_client.cl_count 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 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>
This commit is contained in:
Elena Reshetova
2017-10-20 12:53:38 +03:00
committed by Anna Schumaker
parent 2f62b5aa48
commit 212bf41d88
7 changed files with 33 additions and 32 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
fs/nfs/nfs4client.c
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@@ -483,7 +483,7 @@ static int nfs4_match_client(struct nfs_client *pos, struct nfs_client *new,
* ID and serverowner fields. Wait for CREATE_SESSION
* to finish. */
if (pos->cl_cons_state > NFS_CS_READY) {
atomic_inc(&pos->cl_count);
refcount_inc(&pos->cl_count);
spin_unlock(&nn->nfs_client_lock);
nfs_put_client(*prev);
@@ -559,7 +559,7 @@ int nfs40_walk_client_list(struct nfs_client *new,
* way that a SETCLIENTID_CONFIRM to pos can succeed is
* if new and pos point to the same server:
*/
atomic_inc(&pos->cl_count);
refcount_inc(&pos->cl_count);
spin_unlock(&nn->nfs_client_lock);
nfs_put_client(prev);
@@ -715,7 +715,7 @@ int nfs41_walk_client_list(struct nfs_client *new,
continue;
found:
atomic_inc(&pos->cl_count);
refcount_inc(&pos->cl_count);
*result = pos;
status = 0;
break;
@@ -749,7 +749,7 @@ nfs4_find_client_ident(struct net *net, int cb_ident)
spin_lock(&nn->nfs_client_lock);
clp = idr_find(&nn->cb_ident_idr, cb_ident);
if (clp)
atomic_inc(&clp->cl_count);
refcount_inc(&clp->cl_count);
spin_unlock(&nn->nfs_client_lock);
return clp;
}
@@ -804,7 +804,7 @@ nfs4_find_client_sessionid(struct net *net, const struct sockaddr *addr,
sid->data, NFS4_MAX_SESSIONID_LEN) != 0)
continue;
atomic_inc(&clp->cl_count);
refcount_inc(&clp->cl_count);
spin_unlock(&nn->nfs_client_lock);
return clp;
}