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Subject[PATCH 4.20 096/183] pvcalls-front: fix potential null dereference
Date
4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit b4711098066f1cf808d4dc11a1a842860a3292fe ]

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);
^^^
Add null check on map->active.ring before dereferencing it to avoid
any NULL pointer dereferences.

Fixes: 9f51c05dc41a ("pvcalls-front: Avoid get_free_pages(GFP_KERNEL) under spinlock")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Suggested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>
CC: Juergen Gross <jgross@suse.com>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Dan Carpenter <dan.carpenter@oracle.com>
CC: xen-devel@lists.xenproject.org
CC: linux-kernel@vger.kernel.org
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/xen/pvcalls-front.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
index 6357160d466ab..91da7e44d5d4f 100644
--- a/drivers/xen/pvcalls-front.c
+++ b/drivers/xen/pvcalls-front.c
@@ -343,6 +343,9 @@ int pvcalls_front_socket(struct socket *sock)

static void free_active_ring(struct sock_mapping *map)
{
+ if (!map->active.ring)
+ return;
+
free_pages((unsigned long)map->active.data.in,
map->active.ring->ring_order);
free_page((unsigned long)map->active.ring);
--
2.19.1


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