[PATCH 1/2] mm/mempolicy: Allow lookup_node() to handle fatal signal

Peter Xu
2020-04-08T01:40:21Z

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.

Reported-by: syzbot+693dc11fcb53120b5559@syzkaller.appspotmail.com
Fixes: 4426e945df58 ("mm/gup: allow VM_FAULT_RETRY for multiple times")
Signed-off-by: Peter Xu <peterx@redhat.com>
---
mm/mempolicy.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 5fb427aed612..c7ca6a808fb1 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -897,12 +897,15 @@ 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);
}
--
2.24.1