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@xxxxxxxxxxxx>
Reviewed-by: David Windsor <dwindsor@xxxxxxxxx>
Reviewed-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
---
fs/nfs/pnfs.h | 3 ++-
fs/nfs/pnfs_nfs.c | 10 +++++-----
2 files changed, 7 insertions(+), 6 deletions(-)
diff --git a/fs/nfs/pnfs.h b/fs/nfs/pnfs.h
index 87f144f..cefa7da 100644
--- 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 60da59b..03aaa60 100644
--- 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);
--
2.7.4
--
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