linux-kernel - Re: KASAN: use-after-free Read in filemap

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Date:   Fri, 28 Dec 2018 13:09:38 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     syzbot <syzbot+b437b5a429d680cf2217@...kaller.appspotmail.com>
Cc:     darrick.wong@...cle.com, hannes@...xchg.org, hughd@...gle.com,
        jack@...e.cz, josef@...icpanda.com, jrdr.linux@...il.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        sfr@...b.auug.org.au, syzkaller-bugs@...glegroups.com,
        willy@...radead.org
Subject: Re: KASAN: use-after-free Read in filemap_fault

On Fri, 28 Dec 2018 12:51:04 -0800 syzbot <syzbot+b437b5a429d680cf2217@...kaller.appspotmail.com> wrote:

> Hello,
> 
> syzbot found the following crash on:

uh-oh.  Josef, could you please take a look?

:	page = find_get_page(mapping, offset);
: 	if (likely(page) && !(vmf->flags & FAULT_FLAG_TRIED)) {
: 		/*
: 		 * We found the page, so try async readahead before
: 		 * waiting for the lock.
: 		 */
: 		fpin = do_async_mmap_readahead(vmf, page);
: 	} else if (!page) {
: 		/* No page in the page cache at all */
: 		fpin = do_sync_mmap_readahead(vmf);
: 		count_vm_event(PGMAJFAULT);
: 		count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);

vmf->vma has been freed at this point.

: 		ret = VM_FAULT_MAJOR;
: retry_find:
: 		page = pagecache_get_page(mapping, offset,
: 					  FGP_CREAT|FGP_FOR_MMAP,
: 					  vmf->gfp_mask);
: 		if (!page) {
: 			if (fpin)
: 				goto out_retry;
: 			return vmf_error(-ENOMEM);
: 		}
: 	}