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fs, nfs: convert nfs4_pnfs_ds.ds_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 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>
This commit is contained in:
Elena Reshetova 2017-10-20 12:53:31 +03:00 committed by Anna Schumaker
parent 3be0f80b5f
commit a2a5dea7b6
2 changed files with 7 additions and 6 deletions
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3
fs/nfs/pnfs.h
View File

@ -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 */
};

10
fs/nfs/pnfs_nfs.c
View File

@ -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);