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From:   Javier Martinez Canillas <javierm@redhat.com>
To:     linux-kernel@vger.kernel.org
Cc:     Maxime Ripard <maxime@cerno.tech>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Junxiao Chang <junxiao.chang@intel.com>,
        Javier Martinez Canillas <javierm@redhat.com>,
        dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org
Subject: [PATCH] fbdev: Use helper to get fb_info in all file operations
Date:   Tue,  3 May 2022 18:46:16 +0200
Message-Id: <20220503164616.663796-1-javierm@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

A reference to the framebuffer device struct fb_info is stored in the file
private data, but this reference could no longer be valid and must not be
accessed directly. Instead, the file_fb_info() accessor function must be
used since it does sanity checking to make sure that the fb_info is valid.

This can happen for example if the registered framebuffer device is for a
driver that just uses a framebuffer provided by the system firmware. In
that case, the fbdev core would unregister the framebuffer device when a
real video driver is probed and ask to remove conflicting framebuffers.

Most fbdev file operations already use the helper to get the fb_info but
get_fb_unmapped_area() and fb_deferred_io_fsync() don't. Fix those two.

Since fb_deferred_io_fsync() is not in fbmem.o, the helper has to be
exported. Rename it and add a fb_ prefix to denote that is public now.

Reported-by: Junxiao Chang <junxiao.chang@intel.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
---

 drivers/video/fbdev/core/fb_defio.c |  5 ++++-
 drivers/video/fbdev/core/fbmem.c    | 24 +++++++++++++++---------
 include/linux/fb.h                  |  1 +
 3 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
index 842c66b3e33d..ac1c88b3fbb5 100644
--- a/drivers/video/fbdev/core/fb_defio.c
+++ b/drivers/video/fbdev/core/fb_defio.c
@@ -68,12 +68,15 @@ static vm_fault_t fb_deferred_io_fault(struct vm_fault *vmf)
 
 int fb_deferred_io_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 {
-	struct fb_info *info = file->private_data;
+	struct fb_info *info = fb_file_fb_info(file->private_data);
 	struct inode *inode = file_inode(file);
 	int err = file_write_and_wait_range(file, start, end);
 	if (err)
 		return err;
 
+	if (!info)
+		return -ENODEV;
+
 	/* Skip if deferred io is compiled-in but disabled on this fbdev */
 	if (!info->fbdefio)
 		return 0;
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 97eb0dee411c..f924fda89dd5 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -745,7 +745,7 @@ static const struct seq_operations __maybe_unused proc_fb_seq_ops = {
  * So look up the fb_info using the inode minor number,
  * and just verify it against the reference we have.
  */
-static struct fb_info *file_fb_info(struct file *file)
+struct fb_info *fb_file_fb_info(struct file *file)
 {
 	struct inode *inode = file_inode(file);
 	int fbidx = iminor(inode);
@@ -755,12 +755,13 @@ static struct fb_info *file_fb_info(struct file *file)
 		info = NULL;
 	return info;
 }
+EXPORT_SYMBOL(fb_file_fb_info);
 
 static ssize_t
 fb_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 {
 	unsigned long p = *ppos;
-	struct fb_info *info = file_fb_info(file);
+	struct fb_info *info = fb_file_fb_info(file);
 	u8 *buffer, *dst;
 	u8 __iomem *src;
 	int c, cnt = 0, err = 0;
@@ -825,7 +826,7 @@ static ssize_t
 fb_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
 {
 	unsigned long p = *ppos;
-	struct fb_info *info = file_fb_info(file);
+	struct fb_info *info = fb_file_fb_info(file);
 	u8 *buffer, *src;
 	u8 __iomem *dst;
 	int c, cnt = 0, err = 0;
@@ -1181,7 +1182,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
 
 static long fb_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
-	struct fb_info *info = file_fb_info(file);
+	struct fb_info *info = fb_file_fb_info(file);
 
 	if (!info)
 		return -ENODEV;
@@ -1293,7 +1294,7 @@ static int fb_get_fscreeninfo(struct fb_info *info, unsigned int cmd,
 static long fb_compat_ioctl(struct file *file, unsigned int cmd,
 			    unsigned long arg)
 {
-	struct fb_info *info = file_fb_info(file);
+	struct fb_info *info = fb_file_fb_info(file);
 	const struct fb_ops *fb;
 	long ret = -ENOIOCTLCMD;
 
@@ -1333,7 +1334,7 @@ static long fb_compat_ioctl(struct file *file, unsigned int cmd,
 static int
 fb_mmap(struct file *file, struct vm_area_struct * vma)
 {
-	struct fb_info *info = file_fb_info(file);
+	struct fb_info *info = fb_file_fb_info(file);
 	int (*fb_mmap_fn)(struct fb_info *info, struct vm_area_struct *vma);
 	unsigned long mmio_pgoff;
 	unsigned long start;
@@ -1434,7 +1435,7 @@ fb_release(struct inode *inode, struct file *file)
 __acquires(&info->lock)
 __releases(&info->lock)
 {
-	struct fb_info * const info = file_fb_info(file);
+	struct fb_info * const info = fb_file_fb_info(file);
 
 	if (!info)
 		return -ENODEV;
@@ -1453,8 +1454,13 @@ unsigned long get_fb_unmapped_area(struct file *filp,
 				   unsigned long addr, unsigned long len,
 				   unsigned long pgoff, unsigned long flags)
 {
-	struct fb_info * const info = filp->private_data;
-	unsigned long fb_size = PAGE_ALIGN(info->fix.smem_len);
+	struct fb_info * const info = fb_file_fb_info(filp->private_data);
+	unsigned long fb_size;
+
+	if (!info)
+		return -ENODEV;
+
+	fb_size = PAGE_ALIGN(info->fix.smem_len);
 
 	if (pgoff > fb_size || len > fb_size - pgoff)
 		return -EINVAL;
diff --git a/include/linux/fb.h b/include/linux/fb.h
index 9a77ab615c36..3004b8b8c5c2 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -624,6 +624,7 @@ extern int fb_get_color_depth(struct fb_var_screeninfo *var,
 			      struct fb_fix_screeninfo *fix);
 extern int fb_get_options(const char *name, char **option);
 extern int fb_new_modelist(struct fb_info *info);
+extern struct fb_info *fb_file_fb_info(struct file *file);
 
 extern struct fb_info *registered_fb[FB_MAX];
 extern int num_registered_fb;
-- 
2.35.1