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xen/privcmd: fix error exit of privcmd_ioctl_dm_op()

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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: ab520be8cd ("xen/privcmd: Add IOCTL_PRIVCMD_DM_OP")
Reported-by: Rustam Subkhankulov <subkhankulov@ispras.ru>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Link: https://lore.kernel.org/r/20220825141918.3581-1-jgross@suse.com
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Juergen Gross 2022-08-25 16:19:18 +02:00
parent 6bb79f5b4c
commit c5deb27895
1 changed files with 11 additions and 10 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

21
drivers/xen/privcmd.c
View file

@ -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;
*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);