2019-01-14 03:22:21

by Wen Yang

Subject: [PATCH] pvcalls-front: fix potential null dereference

static checker warning:
drivers/xen/pvcalls-front.c:373 alloc_active_ring()
error: we previously assumed 'map->active.ring' could be null
(see line 357)

drivers/xen/pvcalls-front.c
351 static int alloc_active_ring(struct sock_mapping *map)
352 {
353 void *bytes;
354
355 map->active.ring = (struct pvcalls_data_intf *)
356 get_zeroed_page(GFP_KERNEL);
357 if (!map->active.ring)
^^^^^^^^^^^^^^^^^
Check

358 goto out;
359
360 map->active.ring->ring_order = PVCALLS_RING_ORDER;
361 bytes = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
362 PVCALLS_RING_ORDER);
363 if (!bytes)
364 goto out;
365
366 map->active.data.in = bytes;
367 map->active.data.out = bytes +
368 XEN_FLEX_RING_SIZE(PVCALLS_RING_ORDER);
369
370 return 0;
371
372 out:
--> 373 free_active_ring(map);
^^^
Replace map->active.ring->ring_order with PVCALLS_RING_ORDER
to avoid potential null dereference.

Fixes: 9f51c05dc41a ("pvcalls-front: Avoid get_free_pages(GFP_KERNEL)
under spinlock")
Reported-by: Dan Carpenter <[email protected]>
Signed-off-by: Wen Yang <[email protected]>
CC: Boris Ostrovsky <[email protected]>
CC: Juergen Gross <[email protected]>
CC: Stefano Stabellini <[email protected]>
CC: Dan Carpenter <[email protected]>
CC: [email protected]
CC: [email protected]
---
drivers/xen/pvcalls-front.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
index 307861f..e56f9a3 100644
--- a/drivers/xen/pvcalls-front.c
+++ b/drivers/xen/pvcalls-front.c
@@ -344,7 +344,7 @@ int pvcalls_front_socket(struct socket *sock)
static void free_active_ring(struct sock_mapping *map)
{
free_pages((unsigned long)map->active.data.in,
- map->active.ring->ring_order);
+ PVCALLS_RING_ORDER);
free_page((unsigned long)map->active.ring);
}

--
2.9.5

2019-01-14 16:19:24

by Boris Ostrovsky

Subject: Re: [PATCH] pvcalls-front: fix potential null dereference

On 1/13/19 10:20 PM, Wen Yang wrote:
> static checker warning:
> drivers/xen/pvcalls-front.c:373 alloc_active_ring()
> error: we previously assumed 'map->active.ring' could be null
> (see line 357)
>
> drivers/xen/pvcalls-front.c
> 351 static int alloc_active_ring(struct sock_mapping *map)
> 352 {
> 353 void *bytes;
> 354
> 355 map->active.ring = (struct pvcalls_data_intf *)
> 356 get_zeroed_page(GFP_KERNEL);
> 357 if (!map->active.ring)
> ^^^^^^^^^^^^^^^^^
> Check
>
> 358 goto out;
> 359
> 360 map->active.ring->ring_order = PVCALLS_RING_ORDER;
> 361 bytes = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
> 362 PVCALLS_RING_ORDER);
> 363 if (!bytes)
> 364 goto out;
> 365
> 366 map->active.data.in = bytes;
> 367 map->active.data.out = bytes +
> 368 XEN_FLEX_RING_SIZE(PVCALLS_RING_ORDER);
> 369
> 370 return 0;
> 371
> 372 out:
> --> 373 free_active_ring(map);
> ^^^
> Replace map->active.ring->ring_order with PVCALLS_RING_ORDER
> to avoid potential null dereference.
>
> Fixes: 9f51c05dc41a ("pvcalls-front: Avoid get_free_pages(GFP_KERNEL)
> under spinlock")
> Reported-by: Dan Carpenter <[email protected]>
> Signed-off-by: Wen Yang <[email protected]>
> CC: Boris Ostrovsky <[email protected]>
> CC: Juergen Gross <[email protected]>
> CC: Stefano Stabellini <[email protected]>
> CC: Dan Carpenter <[email protected]>
> CC: [email protected]
> CC: [email protected]
> ---
> drivers/xen/pvcalls-front.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> index 307861f..e56f9a3 100644
> --- a/drivers/xen/pvcalls-front.c
> +++ b/drivers/xen/pvcalls-front.c
> @@ -344,7 +344,7 @@ int pvcalls_front_socket(struct socket *sock)
> static void free_active_ring(struct sock_mapping *map)
> {
> free_pages((unsigned long)map->active.data.in,
> - map->active.ring->ring_order);
> + PVCALLS_RING_ORDER);

I would prefer to have a NULL check on map->active.ring and return
immediately if it is.

Otherwise this code assumes that map->active.ring->ring_order is always
PVCALLS_RING_ORDER, and I don't know whether we want to make this
assumption (even if this is true now).

-boris

> free_page((unsigned long)map->active.ring);
> }
>