In the Linux kernel, the following vulnerability has been resolved:

RDMA/rxe: Fix a use-after-free problem in rxe_mmap

rxe_mmap() removes a rxe_mmap_info struct from the pending_mmaps list
and releases pending_lock while the struct's kref is still at 1:

   list_del_init(&ip->pending_mmaps);
   spin_unlock_bh(&rxe->pending_lock);   /* ref == 1, no lock held */
   ret = remap_vmalloc_range(vma, ip->obj, 0);  /* walks PTEs */
   [...]
   rxe_vma_open(vma);                    /* kref_get, ref → 2 */
   remap_vmalloc_range_partial() walks PTEs without any lock.

A concurrent DESTROY_CQ ioctl on another CPU calls:

    kref_put(&q->ip->ref, rxe_mmap_release)   /* ref 1→0 */
    vfree(ip->obj)   /* clears vmalloc PTEs mid-walk */
    kfree(ip)        /* frees rxe_mmap_info */

This yields:

   1. Kernel crash, vmalloc_to_page() returns NULL when vfree wins the
   per-PTE race -> vm_insert_page(NULL) → GPF in validate_page_before_insert

   2. Page UAF, vmalloc_to_page() reads a stale PTE before vfree clears
   it. User VMA holds a PTE to a free'd page which might eventually get
   reallocated later by vmalloc which allows the attacker to get a clean
   page-level UAF.

   It is worth noting that even though a page-level UAF is possible given
   the strong primitive, it is statistically very difficult to achieve
   given the very short time window (after the last insert_page and before
   the kref_get).

The call trace are as below:

  Oops: general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] SMP KASAN NOPTI
  KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
  CPU: 0 UID: 1000 PID: 413 Comm: poc Not tainted 7.0.0-rc5-dirty #28 PREEMPT(lazy)
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
  RIP: 0010:validate_page_before_insert+0x32/0x300
  Code: e5 41 57 41 56 49 89 fe 41 55 41 54 53 48 89 f3 e8 93 b5 a3 ff 48 8d 7b 08 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 7b 02 00 00 4c 8b 63 08 31 ff 4d 89 

https://git.kernel.org/stable/c/3525987a392536f31a484833af258971af63b24c

https://git.kernel.org/stable/c/35744ab3d03c5fca8c1752f53fc8fc674e14c561

https://git.kernel.org/stable/c/665fb7d22a700c66a78db0cf88c6e6a649aba9d0

https://git.kernel.org/stable/c/e038d42cc09ca1da9d3568ce8ae062b2bfb3bc0e

https://git.kernel.org/stable/c/e59a6aa89e0fcd1d0707832eb4654fd9ae7d31e6

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