Received-SPF: softfail (google.com: domain of transitioning linux-kernel-owner@vger.kernel.org does not designate 23.128.96.19 as permitted sender) client-ip=23.128.96.19;
From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Daniel Vetter <daniel.vetter@ffwll.ch>,
        Daniel Vetter <daniel.vetter@intel.com>,
        Javier Martinez Canillas <javierm@redhat.com>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Sasha Levin <sashal@kernel.org>, daniel@ffwll.ch,
        deller@gmx.de, sam@ravnborg.org, wangqing@vivo.com,
        linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org
Subject: [PATCH AUTOSEL 5.17 08/23] fbdev: Prevent possible use-after-free in fb_release()
Date:   Wed, 18 May 2022 08:26:21 -0400
Message-Id: <20220518122641.342120-8-sashal@kernel.org>
In-Reply-To: <20220518122641.342120-1-sashal@kernel.org>
References: <20220518122641.342120-1-sashal@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

From: Daniel Vetter <daniel.vetter@ffwll.ch>

[ Upstream commit 89bfd4017e58faaf70411555e7f508495114e90b ]

Most fbdev drivers have issues with the fb_info lifetime, because call to
framebuffer_release() from their driver's .remove callback, rather than
doing from fbops.fb_destroy callback.

Doing that will destroy the fb_info too early, while references to it may
still exist, leading to a use-after-free error.

To prevent this, check the fb_info reference counter when attempting to
kfree the data structure in framebuffer_release(). That will leak it but
at least will prevent the mentioned error.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220505220413.365977-1-javierm@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/video/fbdev/core/fbsysfs.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/video/fbdev/core/fbsysfs.c b/drivers/video/fbdev/core/fbsysfs.c
index 26892940c213..82e31a2d845e 100644
--- a/drivers/video/fbdev/core/fbsysfs.c
+++ b/drivers/video/fbdev/core/fbsysfs.c
@@ -80,6 +80,10 @@ void framebuffer_release(struct fb_info *info)
 {
 	if (!info)
 		return;
+
+	if (WARN_ON(refcount_read(&info->count)))
+		return;
+
 	kfree(info->apertures);
 	kfree(info);
 }
-- 
2.35.1