Linux Kernel udlfb UseAfterFree via mmap with missing vm_ops
CVE-2026-43497 Published on May 21, 2026
fbdev: udlfb: add vm_ops to dlfb_ops_mmap to prevent use-after-free
In the Linux kernel, the following vulnerability has been resolved:
fbdev: udlfb: add vm_ops to dlfb_ops_mmap to prevent use-after-free
dlfb_ops_mmap() uses remap_pfn_range() to map vmalloc framebuffer pages
to userspace but sets no vm_ops on the VMA. This means the kernel cannot
track active mmaps. When dlfb_realloc_framebuffer() replaces the backing
buffer via FBIOPUT_VSCREENINFO, existing mmap PTEs are not invalidated.
On USB disconnect, dlfb_ops_destroy() calls vfree() on the old pages
while userspace PTEs still reference them, resulting in a use-after-free:
the process retains read/write access to freed kernel pages.
Add vm_operations_struct with open/close callbacks that maintain an
atomic mmap_count on struct dlfb_data. In dlfb_realloc_framebuffer(),
check mmap_count and return -EBUSY if the buffer is currently mapped,
preventing buffer replacement while userspace holds stale PTEs.
Tested with PoC using dummy_hcd + raw_gadget USB device emulation.
Products Associated with CVE-2026-43497
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Affected Versions
Linux:- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 4f312c30f0368e8d2a76aa650dff73f23490b5e7 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 18dd358de72d57993422cbb5dfb29ccd74efe192 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below da9b065cedfd3b574f229d5be594e6aa47a27ae6 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below a2c53a3822ee26e8d758071815b9ed3bf6669fc1 is affected.
- Version 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and below 8de779dc40d35d39fa07387b6f921eb11df0f511 is affected.
- Version 6.6.140, <= 6.6.* is unaffected.
- Version 6.12.88, <= 6.12.* is unaffected.
- Version 6.18.30, <= 6.18.* is unaffected.
- Version 7.0.7, <= 7.0.* is unaffected.
- Version 7.1-rc3, <= * is unaffected.