From ba841078cd0557b43b59c63f5c048b12168f0db2 Mon Sep 17 00:00:00 2001
From: Peter Xu <peterx@redhat.com>
Date: Tue, 7 Apr 2020 21:40:09 -0400
Subject: [PATCH] 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: 4426e945df58 ("mm/gup: allow VM_FAULT_RETRY for multiple times")
Reported-by: syzbot+693dc11fcb53120b5559@syzkaller.appspotmail.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
mm/mempolicy.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index b4a039d779b0a..fb678a7254f0a 100644
--- 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);
}
--
2.30.2