Hi Am 04.05.22 um 11:02 schrieb Daniel Vetter:
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.
Can we acquire registration_lock around [1]?[1] https://elixir.bootlin.com/linux/v5.17.5/source/drivers/video/fbdev/core/fbmem.c#L756
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_tfb_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
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Ivo Totev
Attachment:
OpenPGP_signature
Description: OpenPGP digital signature
