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: [email protected]
Closes:
https://lore.kernel.org/linux-fbdev/[email protected]/
Assisted-by: Codex:gpt-5
Signed-off-by: Weiming Shi <[email protected]>
---
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 5b7965f36c5ed..de137b2bdaedc 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);
}
}
--
2.55.0
