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Subject[PATCH] ceph: Convert from atomic_t to refcount_t on ceph_snap_realm->nref
Date
refcount_t type and corresponding API can protect refcounters from
accidental underflow and overflow and further use-after-free situations.

Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
---
fs/ceph/snap.c | 15 ++++++++-------
fs/ceph/super.h | 3 ++-
2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index 4ac0606dcbd4..d4ec9c5118bd 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -68,14 +68,15 @@ void ceph_get_snap_realm(struct ceph_mds_client *mdsc,
lockdep_assert_held(&mdsc->snap_rwsem);

dout("get_realm %p %d -> %d\n", realm,
- atomic_read(&realm->nref), atomic_read(&realm->nref)+1);
+ refcount_read(&realm->nref), refcount_read(&realm->nref)+1);
/*
* since we _only_ increment realm refs or empty the empty
* list with snap_rwsem held, adjusting the empty list here is
* safe. we do need to protect against concurrent empty list
* additions, however.
*/
- if (atomic_inc_return(&realm->nref) == 1) {
+ refcount_inc(&realm->nref);
+ if (refcount_read(&realm->nref) == 1) {
spin_lock(&mdsc->snap_empty_lock);
list_del_init(&realm->empty_item);
spin_unlock(&mdsc->snap_empty_lock);
@@ -121,7 +122,7 @@ static struct ceph_snap_realm *ceph_create_snap_realm(
if (!realm)
return ERR_PTR(-ENOMEM);

- atomic_set(&realm->nref, 1); /* for caller */
+ refcount_set(&realm->nref, 1); /* for caller */
realm->ino = ino;
INIT_LIST_HEAD(&realm->children);
INIT_LIST_HEAD(&realm->child_item);
@@ -209,8 +210,8 @@ static void __put_snap_realm(struct ceph_mds_client *mdsc,
lockdep_assert_held_write(&mdsc->snap_rwsem);

dout("__put_snap_realm %llx %p %d -> %d\n", realm->ino, realm,
- atomic_read(&realm->nref), atomic_read(&realm->nref)-1);
- if (atomic_dec_and_test(&realm->nref))
+ refcount_read(&realm->nref), refcount_read(&realm->nref)-1);
+ if (refcount_dec_and_test(&realm->nref))
__destroy_snap_realm(mdsc, realm);
}

@@ -221,8 +222,8 @@ void ceph_put_snap_realm(struct ceph_mds_client *mdsc,
struct ceph_snap_realm *realm)
{
dout("put_snap_realm %llx %p %d -> %d\n", realm->ino, realm,
- atomic_read(&realm->nref), atomic_read(&realm->nref)-1);
- if (!atomic_dec_and_test(&realm->nref))
+ refcount_read(&realm->nref), refcount_read(&realm->nref)-1);
+ if (!refcount_dec_and_test(&realm->nref))
return;

if (down_write_trylock(&mdsc->snap_rwsem)) {
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index 6b6332a5c113..3abb00d7a0eb 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -2,6 +2,7 @@
#ifndef _FS_CEPH_SUPER_H
#define _FS_CEPH_SUPER_H

+#include <linux/refcount.h>
#include <linux/ceph/ceph_debug.h>

#include <asm/unaligned.h>
@@ -859,7 +860,7 @@ struct ceph_readdir_cache_control {
struct ceph_snap_realm {
u64 ino;
struct inode *inode;
- atomic_t nref;
+ refcount_t nref;
struct rb_node node;

u64 created, seq;
--
2.7.4
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