ANDROID: mm: avoid using vmacache in lockless vma search

When searching vma under RCU protection vmcache should be avoided because
a race with munmap() might result in finding a vma and placing it into
vmcache after munmap() removed that vma and called vmcache_invalidate.
Once that vma is freed, vmcache will be left with an invalid vma pointer.

Bug: 257443051
Change-Id: I62438305fcf5139974f4f7d3bae5b22c74084a59
Signed-off-by: Suren Baghdasaryan <surenb@google.com>

include/linux/mm.h

@@ -2734,6 +2734,8 @@ extern int expand_upwards(struct vm_area_struct *vma, unsigned long address);
   #define expand_upwards(vma, address) (0)
 #endif
 
+extern struct vm_area_struct *find_vma_from_tree(struct mm_struct *mm,
+						 unsigned long addr);
 /* Look up the first VMA which satisfies  addr < vm_end,  NULL if none. */
 extern struct vm_area_struct * __find_vma(struct mm_struct * mm, unsigned long addr);
 extern struct vm_area_struct * find_vma_prev(struct mm_struct * mm, unsigned long addr,

mm/memory.c

@@ -216,7 +216,7 @@ struct vm_area_struct *get_vma(struct mm_struct *mm, unsigned long addr)
 	struct vm_area_struct *vma;
 
 	rcu_read_lock();
-	vma = __find_vma(mm, addr);
+	vma = find_vma_from_tree(mm, addr);
 	if (vma) {
 		if (vma->vm_start > addr ||
 		    !atomic_inc_unless_negative(&vma->file_ref_count))

mm/mmap.c

@@ -2279,16 +2279,10 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
 
 EXPORT_SYMBOL(get_unmapped_area);
 
-/* Look up the first VMA which satisfies  addr < vm_end,  NULL if none. */
-struct vm_area_struct *__find_vma(struct mm_struct *mm, unsigned long addr)
+struct vm_area_struct *find_vma_from_tree(struct mm_struct *mm, unsigned long addr)
 {
 	struct rb_node *rb_node;
-	struct vm_area_struct *vma;
-
-	/* Check the cache first. */
-	vma = vmacache_find(mm, addr);
-	if (likely(vma))
-		return vma;
+	struct vm_area_struct *vma = NULL;
 
 	rb_node = mm->mm_rb.rb_node;
 
@@ -2306,6 +2300,21 @@ struct vm_area_struct *__find_vma(struct mm_struct *mm, unsigned long addr)
 			rb_node = rb_node->rb_right;
 	}
 
+	return vma;
+}
+
+/* Look up the first VMA which satisfies  addr < vm_end,  NULL if none. */
+struct vm_area_struct *__find_vma(struct mm_struct *mm, unsigned long addr)
+{
+	struct vm_area_struct *vma;
+
+	/* Check the cache first. */
+	vma = vmacache_find(mm, addr);
+	if (likely(vma))
+		return vma;
+
+	vma = find_vma_from_tree(mm, addr);
+
 	if (vma)
 		vmacache_update(addr, vma);
 	return vma;

mm/nommu.c

@@ -659,6 +659,22 @@ static void delete_vma(struct mm_struct *mm, struct vm_area_struct *vma)
 	vm_area_free(vma);
 }
 
+struct vm_area_struct *find_vma_from_tree(struct mm_struct *mm, unsigned long addr)
+{
+	struct vm_area_struct *vma;
+
+	/* trawl the list (there may be multiple mappings in which addr
+	 * resides) */
+	for (vma = mm->mmap; vma; vma = vma->vm_next) {
+		if (vma->vm_start > addr)
+			return NULL;
+		if (vma->vm_end > addr)
+			return vma;
+	}
+
+	return NULL;
+}
+
 /*
  * look up the first VMA in which addr resides, NULL if none
  * - should be called with mm->mmap_lock at least held readlocked
@@ -667,24 +683,17 @@ struct vm_area_struct *__find_vma(struct mm_struct *mm, unsigned long addr)
 {
 	struct vm_area_struct *vma;
 
-	/* check the cache first */
+	/* Check the cache first. */
 	vma = vmacache_find(mm, addr);
 	if (likely(vma))
 		return vma;
 
-	/* trawl the list (there may be multiple mappings in which addr
-	 * resides) */
-	for (vma = mm->mmap; vma; vma = vma->vm_next) {
-		if (vma->vm_start > addr)
-			return NULL;
-		if (vma->vm_end > addr) {
+	vma = find_vma_from_tree(mm, addr);
+
+	if (vma)
 		vmacache_update(addr, vma);
 	return vma;
 }
-	}
-
-	return NULL;
-}
 EXPORT_SYMBOL(__find_vma);
 
 /*