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fbdev: vfb: defer cleanup until the last reference

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FBIOGETCMAP takes a shallow snapshot of info->cmap and performs the
usercopy after dropping info->lock. vfb_remove() frees the colormap
immediately after unregistering the framebuffer, even when an open file
still holds a reference to fb_info. A concurrent driver unbind can
therefore free the colormap while the ioctl copies it to userspace.

KASAN reports:

  BUG: KASAN: slab-use-after-free in _copy_to_user
  Read of size 512 by task poc/125

   _copy_to_user (./include/linux/instrumented.h:129 ./include/linux/uaccess.h:201 lib/usercopy.c:24)
   fb_cmap_to_user (./include/linux/uaccess.h:230 drivers/video/fbdev/core/fbcmap.c:211)
   do_fb_ioctl (drivers/video/fbdev/core/fb_chrdev.c:114)

   Allocated by task 1:
   fb_alloc_cmap_gfp (./include/linux/slab.h:973 ./include/linux/slab.h:1290 drivers/video/fbdev/core/fbcmap.c:108)
   vfb_probe (drivers/video/fbdev/vfb.c:459)

   Freed by task 124:
   fb_dealloc_cmap (drivers/video/fbdev/core/fbcmap.c:151)
   vfb_remove (drivers/video/fbdev/vfb.c:489)

unregister_framebuffer() drops the registration reference, and fbdev calls
fb_destroy after the last put_fb_info(). Move the registered framebuffer's
cleanup into an fb_destroy callback so its colormap and screen buffer stay
alive until all file references have been released.

Fixes: 5e266e2e0e ("vfb: fix memory leaks in removal path")
Reported-by: co+c25629c98ba36ebe@bugs.sh
Cc: stable@kernel.org
Closes: https://lore.kernel.org/linux-fbdev/f2Kf9GYn1lKR5S1dbvGVtykMxK1RlgP5z8sW@bugs.sh/
Assisted-by: Codex:gpt-5
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Link: https://lore.kernel.org/linux-fbdev/f2Kf9GYn1lKR5S1dbvGVtykMxK1RlgP5z8sW@bugs.sh/
Signed-off-by: Helge Deller <deller@gmx.de>
This commit is contained in:
Weiming Shi 2026-09-10 03:10:23 +08:00 committed by Helge Deller
parent 3934185ba6
commit a0a34a40ed
1 changed files with 8 additions and 3 deletions
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11
drivers/video/fbdev/vfb.c
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@ -78,6 +78,13 @@ static int vfb_pan_display(struct fb_var_screeninfo *var,
static int vfb_mmap(struct fb_info *info,
struct vm_area_struct *vma);
static void vfb_destroy(struct fb_info *info)
{
vfree(info->screen_buffer);
fb_dealloc_cmap(&info->cmap);
framebuffer_release(info);
}
static const struct fb_ops vfb_ops = {
.owner = THIS_MODULE,
__FB_DEFAULT_SYSMEM_OPS_RDWR,
@ -87,6 +94,7 @@ static const struct fb_ops vfb_ops = {
.fb_pan_display = vfb_pan_display,
__FB_DEFAULT_SYSMEM_OPS_DRAW,
.fb_mmap = vfb_mmap,
.fb_destroy = vfb_destroy,
};
/*
@ -485,9 +493,6 @@ static void vfb_remove(struct platform_device *dev)
if (info) {
unregister_framebuffer(info);
vfree(videomemory);
fb_dealloc_cmap(&info->cmap);
framebuffer_release(info);
}
}