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

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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: 4426e945df ("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>
This commit is contained in:
Peter Xu 2020-04-07 21:40:09 -04:00 committed by Linus Torvalds
parent 63bef48fd6
commit ba841078cd
1 changed files with 5 additions and 2 deletions
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7
mm/mempolicy.c
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@ -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);
}