Commit ba841078 authored Apr 07, 2020 by Peter Xu Committed by Linus Torvalds Apr 07, 2020

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: 4426e945 ("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>

parent 63bef48f

mm/mempolicy.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -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);
		}

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