diff options
| author | Juergen Gross | 2026-04-10 09:20:04 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman | 2026-04-30 11:13:05 +0200 |
| commit | 71bf829800758a6e3889096e4754ef47ba7fc850 (patch) | |
| tree | 8531ae931cfade7902af6ad338de461b5ee53b7d | |
| parent | 52cecff98bda2c51eed1c6ce9d21c5d6268fb19d (diff) | |
xen/privcmd: fix double free via VMA splitting
commit 24daca4fc07f3ff8cd0e3f629cd982187f48436a upstream.
privcmd_vm_ops defines .close (privcmd_close), but neither .may_split
nor .open. When userspace does a partial munmap() on a privcmd mapping,
the kernel splits the VMA via __split_vma(). Since may_split is NULL,
the split is allowed. vm_area_dup() copies vm_private_data (a pages
array allocated in alloc_empty_pages()) into the new VMA without any
fixup, because there is no .open callback.
Both VMAs now point to the same pages array. When the unmapped portion
is closed, privcmd_close() calls:
- xen_unmap_domain_gfn_range()
- xen_free_unpopulated_pages()
- kvfree(pages)
The surviving VMA still holds the dangling pointer. When it is later
destroyed, the same sequence runs again, which leads to a double free.
Fix this issue by adding a .may_split callback denying the VMA split.
This is XSA-487 / CVE-2026-31787
Fixes: d71f513985c2 ("xen: privcmd: support autotranslated physmap guests.")
Reported-by: Atharva Vartak <atharva.a.vartak@gmail.com>
Suggested-by: Atharva Vartak <atharva.a.vartak@gmail.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | drivers/xen/privcmd.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c index 15ba592236e8..725a49a0eee7 100644 --- a/drivers/xen/privcmd.c +++ b/drivers/xen/privcmd.c @@ -1620,6 +1620,12 @@ static void privcmd_close(struct vm_area_struct *vma) kvfree(pages); } +static int privcmd_may_split(struct vm_area_struct *area, unsigned long addr) +{ + /* Forbid splitting, avoids double free via privcmd_close(). */ + return -EINVAL; +} + static vm_fault_t privcmd_fault(struct vm_fault *vmf) { printk(KERN_DEBUG "privcmd_fault: vma=%p %lx-%lx, pgoff=%lx, uv=%p\n", @@ -1631,6 +1637,7 @@ static vm_fault_t privcmd_fault(struct vm_fault *vmf) static const struct vm_operations_struct privcmd_vm_ops = { .close = privcmd_close, + .may_split = privcmd_may_split, .fault = privcmd_fault }; |