On 25.08.22 17:19, Juergen Gross wrote:

Hello Juergen

The error exit of privcmd_ioctl_dm_op() is calling unlock_pages() potentially with pages being NULL, leading to a NULL dereference.

Additionally lock_pages() doesn't check for pin_user_pages_fast() having been completely successful, resulting in potentially not locking all pages into memory. This could result in sporadic failures when using the related memory in user mode.

Fix all of that by calling unlock_pages() always with the real number of pinned pages, which will be zero in case pages being NULL, and by checking the number of pages pinned by pin_user_pages_fast() matching the expected number of pages.

Cc: stable@vger.kernel.org Fixes: ab520be8cd5d ("xen/privcmd: Add IOCTL_PRIVCMD_DM_OP") Reported-by: Rustam Subkhankulov subkhankulov@ispras.ru Signed-off-by: Juergen Gross jgross@suse.com

I haven't spotted any issues:

Reviewed-by: Oleksandr Tyshchenko oleksandr_tyshchenko@epam.com

---

V2:

• use "pinned" as parameter for unlock_pages() (Jan Beulich)
• drop label "unlock" again (Jan Beulich)
• add check for complete success of pin_user_pages_fast()

V3:

• continue after partial success of pin_user_pages_fast() (Jan Beulich)

V4:

• fix case of multiple partial successes for one buffer (Jan Beulich)

---

drivers/xen/privcmd.c | 21 +++++++++++---------- 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c index 3369734108af..e88e8f6f0a33 100644 --- a/drivers/xen/privcmd.c +++ b/drivers/xen/privcmd.c @@ -581,27 +581,30 @@ static int lock_pages( struct privcmd_dm_op_buf kbufs[], unsigned int num, struct page *pages[], unsigned int nr_pages, unsigned int *pinned) {

• unsigned int i;

• unsigned int i, off = 0;

• for (i = 0; i < num; i++) {

• for (i = 0; i < num; ) { unsigned int requested; int page_count;

requested = DIV_ROUND_UP( offset_in_page(kbufs[i].uptr) + kbufs[i].size,

• 	PAGE_SIZE);
  

• 	PAGE_SIZE) - off;
  

  if (requested > nr_pages) return -ENOSPC;

page_count = pin_user_pages_fast(

• 	(unsigned long) kbufs[i].uptr,
  

• 	(unsigned long)kbufs[i].uptr + off * PAGE_SIZE,
  requested, FOLL_WRITE, pages);
  

• if (page_count < 0)
  

• 	return page_count;
  

• if (page_count <= 0)
  

• 	return page_count ? : -EFAULT;
  

[not related to the current patch]

I just wonder, whether drivers/xen/gntdev.c:gntdev_get_page() really wants to gain the same check?

index 59ffea800079..45e16031204d 100644 --- a/drivers/xen/gntdev.c +++ b/drivers/xen/gntdev.c @@ -740,8 +740,8 @@ static int gntdev_get_page(struct gntdev_copy_batch *batch, void __user *virt,         int ret;

ret = pin_user_pages_fast(addr, 1, batch->writeable ? FOLL_WRITE : 0, &page); -       if (ret < 0) -               return ret; +       if (ret <= 0) +               return ret ? : -EFAULT;

batch->pages[batch->nr_pages++] = page;

*pinned += page_count; nr_pages -= page_count; pages += page_count;

• off = (requested == page_count) ? 0 : off + page_count;
  

• i += !off;
  

  }

return 0; @@ -677,10 +680,8 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata) } rc = lock_pages(kbufs, kdata.num, pages, nr_pages, &pinned);

• if (rc < 0) {

• nr_pages = pinned;
  

• if (rc < 0) goto out;

• }

for (i = 0; i < kdata.num; i++) { set_xen_guest_handle(xbufs[i].h, kbufs[i].uptr); @@ -692,7 +693,7 @@ static long privcmd_ioctl_dm_op(struct file *file, void __user *udata) xen_preemptible_hcall_end(); out:

• unlock_pages(pages, nr_pages);

• unlock_pages(pages, pinned); kfree(xbufs); kfree(pages); kfree(kbufs);