[PATCH 5.15 116/136] xen/privcmd: fix error exit of privcmd_ioctl_dm_op()

[Greg Kroah-Hartman]

From: Juergen Gross <jgross@xxxxxxxx>

commit c5deb27895e017a0267de0a20d140ad5fcc55a54 upstream.

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@xxxxxxxxxxxxxxx>
Fixes: ab520be8cd5d ("xen/privcmd: Add IOCTL_PRIVCMD_DM_OP")
Reported-by: Rustam Subkhankulov <subkhankulov@xxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
Link: https://lore.kernel.org/r/20220825141918.3581-1-jgross@xxxxxxxx
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/xen/privcmd.c |   21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

--- 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;
 
 		*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 f
 	}
 
 	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 f
 	xen_preemptible_hcall_end();
 
 out:
-	unlock_pages(pages, nr_pages);
+	unlock_pages(pages, pinned);
 	kfree(xbufs);
 	kfree(pages);
 	kfree(kbufs);