On Tue, May 03, 2022 at 10:19:34PM +0200, Javier Martinez Canillas wrote: > 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@xxxxxxxxx> > Signed-off-by: Javier Martinez Canillas <javierm@xxxxxxxxxx> Note that fb_file_info is hilariously racy since there's nothing preventing a concurrenct framebuffer_unregister. Or at least I'm not seeing anything. See cf4a3ae4ef33 ("fbdev: lock_fb_info cannot fail") for context, maybe reference that commit here in your patch. Either way this doesn't really make anything worse, so Acked-by: Daniel Vetter <daniel.vetter@xxxxxxxx> Cheers, Daniel > --- > > Changes in v2: > - Fix copy & paste error passing file->private_data instead of file > to fb_file_fb_info() function (Sam Ravnborg). > > 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..ccdf903c48bd 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); > 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..ba2c14a1087d 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); > + 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 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch