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 tcon_link.tl_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/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 de5b2e1..18963bf 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>
#include "smb2pdu.h"
@@ -974,7 +975,7 @@ 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;
};
@@ -992,7 +993,7 @@ 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 0bfc228..f861152 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -2868,7 +2868,7 @@ 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;
@@ -4328,7 +4328,7 @@ 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? */
@@ -4406,11 +4406,11 @@ 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
--
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