linux-kernel - [PATCH 2/3] fs, fuse: convert fuse_req.count from atomic_t to refcount

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Date:   Fri,  3 Mar 2017 11:04:04 +0200
From:   Elena Reshetova <elena.reshetova@...el.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-fsdevel@...r.kernel.org, peterz@...radead.org,
        gregkh@...uxfoundation.org, miklos@...redi.hu,
        Elena Reshetova <elena.reshetova@...el.com>,
        Hans Liljestrand <ishkamiel@...il.com>,
        Kees Cook <keescook@...omium.org>,
        David Windsor <dwindsor@...il.com>
Subject: [PATCH 2/3] fs, fuse: convert fuse_req.count from atomic_t to refcount_t

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@...el.com>
Signed-off-by: Hans Liljestrand <ishkamiel@...il.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
Signed-off-by: David Windsor <dwindsor@...il.com>
---
 fs/fuse/dev.c    | 10 +++++-----
 fs/fuse/fuse_i.h |  2 +-
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index f117926..3e67205 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -44,7 +44,7 @@ static void fuse_request_init(struct fuse_req *req, struct page **pages,
 	INIT_LIST_HEAD(&req->list);
 	INIT_LIST_HEAD(&req->intr_entry);
 	init_waitqueue_head(&req->waitq);
-	atomic_set(&req->count, 1);
+	refcount_set(&req->count, 1);
 	req->pages = pages;
 	req->page_descs = page_descs;
 	req->max_pages = npages;
@@ -101,14 +101,14 @@ void fuse_request_free(struct fuse_req *req)
 
 void __fuse_get_request(struct fuse_req *req)
 {
-	atomic_inc(&req->count);
+	refcount_inc(&req->count);
 }
 
 /* Must be called with > 1 refcount */
 static void __fuse_put_request(struct fuse_req *req)
 {
-	BUG_ON(atomic_read(&req->count) < 2);
-	atomic_dec(&req->count);
+	BUG_ON(refcount_read(&req->count) < 2);
+	refcount_dec(&req->count);
 }
 
 static void fuse_req_init_context(struct fuse_req *req)
@@ -263,7 +263,7 @@ struct fuse_req *fuse_get_req_nofail_nopages(struct fuse_conn *fc,
 
 void fuse_put_request(struct fuse_conn *fc, struct fuse_req *req)
 {
-	if (atomic_dec_and_test(&req->count)) {
+	if (refcount_dec_and_test(&req->count)) {
 		if (test_bit(FR_BACKGROUND, &req->flags)) {
 			/*
 			 * We get here in the unlikely case that a background
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 1d6d67e..9d43740 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -307,7 +307,7 @@ struct fuse_req {
 	struct list_head intr_entry;
 
 	/** refcount */
-	atomic_t count;
+	refcount_t count;
 
 	/** Unique ID for the interrupt request */
 	u64 intr_unique;
-- 
2.7.4