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Shutemov" To: Andrew Morton Cc: syzbot , darrick.wong@oracle.com, hannes@cmpxchg.org, hughd@google.com, jack@suse.cz, josef@toxicpanda.com, jrdr.linux@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, sfr@canb.auug.org.au, syzkaller-bugs@googlegroups.com, willy@infradead.org Subject: Re: KASAN: use-after-free Read in filemap_fault Message-ID: <20181228235106.okk3oastsnpxusxs@kshutemo-mobl1> References: <000000000000b57d19057e1b383d@google.com> <20181228130938.c9e42c213cdcc35a93dd0dac@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181228130938.c9e42c213cdcc35a93dd0dac@linux-foundation.org> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 28, 2018 at 01:09:38PM -0800, Andrew Morton wrote: > On Fri, 28 Dec 2018 12:51:04 -0800 syzbot 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); > : } > : } > Here's a fixup for "filemap: drop the mmap_sem for all blocking operations". do_sync_mmap_readahead() drops mmap_sem now, so by the time of dereferencing vmf->vma for count_memcg_event_mm() the VMA can be gone. diff --git a/mm/filemap.c b/mm/filemap.c index 00a9315f45d4..65c85c47bdb1 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2554,10 +2554,10 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) 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); ret = VM_FAULT_MAJOR; + fpin = do_sync_mmap_readahead(vmf); retry_find: page = pagecache_get_page(mapping, offset, FGP_CREAT|FGP_FOR_MMAP, -- Kirill A. Shutemov