[PATCH] tee: shm: don't put_page on null shm->pages

[Colin King]

From: Colin Ian King <colin.k...@canonical.com>

In the case that shm->pages fails to allocate, the current exit
error path will try to put_page on a null shm->pages and cause
a null pointer dereference when accessing shm->pages[n]. Fix this
by only performing the put_page and kfree on shm->pages if it
is not null.

Detected by CoverityScan, CID#1463283 ("Dereference after null check")

Fixes: 033ddf12bcf5 ("tee: add register user memory")
Signed-off-by: Colin Ian King <colin.k...@canonical.com>
---
 drivers/tee/tee_shm.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
index 13b4de1157c7..6890c8aaef8c 100644
--- a/drivers/tee/tee_shm.c
+++ b/drivers/tee/tee_shm.c
@@ -335,9 +335,11 @@ struct tee_shm *tee_shm_register(struct tee_context *ctx, 
unsigned long addr,
                        idr_remove(&teedev->idr, shm->id);
                        mutex_unlock(&teedev->mutex);
                }
-               for (n = 0; n < shm->num_pages; n++)
-                       put_page(shm->pages[n]);
-               kfree(shm->pages);
+               if (shm->pages) {
+                       for (n = 0; n < shm->num_pages; n++)
+                               put_page(shm->pages[n]);
+                       kfree(shm->pages);
+               }
        }
        kfree(shm);
        teedev_ctx_put(ctx);
-- 
2.14.1