From b2d84dbf3bb684d4161e8c32c9950a03a9679c08 Mon Sep 17 00:00:00 2001
From: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Date: Mon, 19 Jul 2021 13:59:45 +0800
Subject: fbmem: Convert from atomic_t to refcount_t on fb_info->count
Git-commit: 0189cb57b96ff92f75e3680b3710a46dacd6509f
Patch-mainline: v5.15-rc1
References: jsc#PED-1166 jsc#PED-1168 jsc#PED-1170 jsc#PED-1218 jsc#PED-1220 jsc#PED-1222 jsc#PED-1223 jsc#PED-1225

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>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1626674392-55857-1-git-send-email-xiyuyang19@fudan.edu.cn
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 drivers/video/fbdev/core/fbmem.c | 6 +++---
 include/linux/fb.h               | 3 ++-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 1c855145711b..71fb710f1ce3 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -67,7 +67,7 @@ static struct fb_info *get_fb_info(unsigned int idx)
 	mutex_lock(&registration_lock);
 	fb_info = registered_fb[idx];
 	if (fb_info)
-		atomic_inc(&fb_info->count);
+		refcount_inc(&fb_info->count);
 	mutex_unlock(&registration_lock);
 
 	return fb_info;
@@ -75,7 +75,7 @@ static struct fb_info *get_fb_info(unsigned int idx)
 
 static void put_fb_info(struct fb_info *fb_info)
 {
-	if (!atomic_dec_and_test(&fb_info->count))
+	if (!refcount_dec_and_test(&fb_info->count))
 		return;
 	if (fb_info->fbops->fb_destroy)
 		fb_info->fbops->fb_destroy(fb_info);
@@ -1592,7 +1592,7 @@ static int do_register_framebuffer(struct fb_info *fb_info)
 		if (!registered_fb[i])
 			break;
 	fb_info->node = i;
-	atomic_set(&fb_info->count, 1);
+	refcount_set(&fb_info->count, 1);
 	mutex_init(&fb_info->lock);
 	mutex_init(&fb_info->mm_lock);
 
diff --git a/include/linux/fb.h b/include/linux/fb.h
index ecfbcc0553a5..5950f8f5dc74 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -2,6 +2,7 @@
 #ifndef _LINUX_FB_H
 #define _LINUX_FB_H
 
+#include <linux/refcount.h>
 #include <linux/kgdb.h>
 #include <uapi/linux/fb.h>
 
@@ -435,7 +436,7 @@ struct fb_tile_ops {
 
 
 struct fb_info {
-	atomic_t count;
+	refcount_t count;
 	int node;
 	int flags;
 	/*
-- 
2.38.1