[PATCH] xen/gntdev: fix gntdev_mmap() error exit path

[Juergen Gross <jgross@xxxxxxxx>]

Commit d3eeb1d77c5d0af ("xen/gntdev: use mmu_interval_notifier_insert")
introduced an error in gntdev_mmap(): in case the call of
mmu_interval_notifier_insert_locked() fails the exit path should not
call mmu_interval_notifier_remove(), as this might result in NULL
dereferences.

One reason for failure is e.g. a signal pending for the running
process.

Fixes: d3eeb1d77c5d0af ("xen/gntdev: use mmu_interval_notifier_insert")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
Tested-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 drivers/xen/gntdev.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index f01d58c7a042..a3e7be96527d 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -1017,8 +1017,10 @@ static int gntdev_mmap(struct file *flip, struct 
vm_area_struct *vma)
                err = mmu_interval_notifier_insert_locked(
                        &map->notifier, vma->vm_mm, vma->vm_start,
                        vma->vm_end - vma->vm_start, &gntdev_mmu_ops);
-               if (err)
+               if (err) {
+                       map->vma = NULL;
                        goto out_unlock_put;
+               }
        }
        mutex_unlock(&priv->lock);
 
-- 
2.26.2