mm/vma: support vma == NULL in init_vma_munmap()

Adding support for a NULL vma means the init_vma_munmap() can be
initialized for a less error-prone process when calling
vms_complete_munmap_vmas() later on.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Liam R. Howlett <[email protected]>
Reviewed-by: Lorenzo Stoakes <[email protected]>
Cc: Bert Karwatzki <[email protected]>
Cc: Jeff Xu <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Mark Brown <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: Paul Moore <[email protected]>
Cc: Sidhartha Kumar <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

2 files changed, 9 insertions, 4 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index 84cb4b1df4a2..ac348ae933ba 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1393,11 +1393,11 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 
 	/* Find the first overlapping VMA */
 	vma = vma_find(&vmi, end);
+	init_vma_munmap(&vms, &vmi, vma, addr, end, uf, /* unlock = */ false);
 	if (vma) {
 		mt_init_flags(&mt_detach, vmi.mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
 		mt_on_stack(mt_detach);
 		mas_init(&mas_detach, &mt_detach, /* addr = */ 0);
-		init_vma_munmap(&vms, &vmi, vma, addr, end, uf, /* unlock = */ false);
 		/* Prepare to unmap any existing mapping in the area */
 		error = vms_gather_munmap_vmas(&vms, &mas_detach);
 		if (error)
diff --git a/mm/vma.h b/mm/vma.h
index e78b24d1cf83..0e214bbf443e 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -95,9 +95,14 @@ static inline void init_vma_munmap(struct vma_munmap_struct *vms,
 {
 	vms->vmi = vmi;
 	vms->vma = vma;
-	vms->mm = vma->vm_mm;
-	vms->start = start;
-	vms->end = end;
+	if (vma) {
+		vms->mm = vma->vm_mm;
+		vms->start = start;
+		vms->end = end;
+	} else {
+		vms->mm = NULL;
+		vms->start = vms->end = 0;
+	}
 	vms->unlock = unlock;
 	vms->uf = uf;
 	vms->vma_count = 0;