From a0a34a40ed299c9c7cff6af163a5b883ee9d6d73 Mon Sep 17 00:00:00 2001 From: Weiming Shi Date: Thu, 10 Sep 2026 03:10:23 +0800 Subject: [PATCH] fbdev: vfb: defer cleanup until the last reference 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: 5e266e2e0e19 ("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 Link: https://lore.kernel.org/linux-fbdev/f2Kf9GYn1lKR5S1dbvGVtykMxK1RlgP5z8sW@bugs.sh/ Signed-off-by: Helge Deller --- drivers/video/fbdev/vfb.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/drivers/video/fbdev/vfb.c b/drivers/video/fbdev/vfb.c index 5b7965f36c5e..de137b2bdaed 100644 --- a/drivers/video/fbdev/vfb.c +++ b/drivers/video/fbdev/vfb.c @@ -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); } }