mm/mempolicy: Allow lookup_node() to handle fatal signal

lookup_node() uses gup to pin the page and get node information. It checks against ret>=0 assuming the page will be filled in. However it's also possible that gup will return zero, for example, when the thread is quickly killed with a fatal signal. Teach lookup_node() to gracefully return an error -EFAULT if it happens. Meanwhile, initialize "page" to NULL to avoid potential risk of exploiting the pointer. Fixes: 4426e94 ("mm/gup: allow VM_FAULT_RETRY for multiple times") Reported-by: [email protected] Signed-off-by: Peter Xu <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
laijs · Apr 8, 2020 · ba84107 · ba84107
1 parent 63bef48
commit ba84107
Showing 1 changed file with 5 additions and 2 deletions.
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
@@ -896,12 +896,15 @@ static void get_policy_nodemask(struct mempolicy *p, nodemask_t *nodes)
 
 static int lookup_node(struct mm_struct *mm, unsigned long addr)
 {
-	struct page *p;
+	struct page *p = NULL;
 	int err;
 
 	int locked = 1;
 	err = get_user_pages_locked(addr & PAGE_MASK, 1, 0, &p, &locked);
-	if (err >= 0) {
+	if (err == 0) {
+		/* E.g. GUP interrupted by fatal signal */
+		err = -EFAULT;
+	} else if (err > 0) {
 		err = page_to_nid(p);
 		put_page(p);
 	}