[PATCH 10/10] fs, cifs: convert tcon_link.tl_count from atomic_t to refcount_t

From: Elena Reshetova
Date: Thu Mar 02 2017 - 07:26:19 EST


refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
Signed-off-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: David Windsor <dwindsor@xxxxxxxxx>
---
fs/cifs/cifsglob.h | 5 +++--
fs/cifs/connect.c | 8 ++++----
2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 1a90bb3..bd27f92 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -28,6 +28,7 @@
#include "cifsacl.h"
#include <crypto/internal/hash.h>
#include <linux/scatterlist.h>
+#include <linux/refcount.h>
#include <uapi/linux/cifs/cifs_mount.h>
#ifdef CONFIG_CIFS_SMB2
#include "smb2pdu.h"
@@ -978,7 +979,7 @@ struct tcon_link {
#define TCON_LINK_PENDING 1
#define TCON_LINK_IN_TREE 2
unsigned long tl_time;
- atomic_t tl_count;
+ refcount_t tl_count;
struct cifs_tcon *tl_tcon;
};

@@ -996,7 +997,7 @@ static inline struct tcon_link *
cifs_get_tlink(struct tcon_link *tlink)
{
if (tlink && !IS_ERR(tlink))
- atomic_inc(&tlink->tl_count);
+ refcount_inc(&tlink->tl_count);
return tlink;
}

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 777ad9f..e0f37ab 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -2839,7 +2839,7 @@ cifs_put_tlink(struct tcon_link *tlink)
if (!tlink || IS_ERR(tlink))
return;

- if (!atomic_dec_and_test(&tlink->tl_count) ||
+ if (!refcount_dec_and_test(&tlink->tl_count) ||
test_bit(TCON_LINK_IN_TREE, &tlink->tl_flags)) {
tlink->tl_time = jiffies;
return;
@@ -4302,7 +4302,7 @@ cifs_sb_tlink(struct cifs_sb_info *cifs_sb)
newtlink->tl_tcon = ERR_PTR(-EACCES);
set_bit(TCON_LINK_PENDING, &newtlink->tl_flags);
set_bit(TCON_LINK_IN_TREE, &newtlink->tl_flags);
- cifs_get_tlink(newtlink);
+ refcount_set(&newtlink->tl_count, 1);

spin_lock(&cifs_sb->tlink_tree_lock);
/* was one inserted after previous search? */
@@ -4380,11 +4380,11 @@ cifs_prune_tlinks(struct work_struct *work)
tlink = rb_entry(tmp, struct tcon_link, tl_rbnode);

if (test_bit(TCON_LINK_MASTER, &tlink->tl_flags) ||
- atomic_read(&tlink->tl_count) != 0 ||
+ refcount_read(&tlink->tl_count) != 0 ||
time_after(tlink->tl_time + TLINK_IDLE_EXPIRE, jiffies))
continue;

- cifs_get_tlink(tlink);
+ refcount_set(&tlink->tl_count, 1);
clear_bit(TCON_LINK_IN_TREE, &tlink->tl_flags);
rb_erase(tmp, root);

--
2.7.4