On Sun, Nov 26, 2017 at 10:15:17PM -0800, Eric Biggers wrote: > +Cc aarcange@xxxxxxxxxx, xemul@xxxxxxxxxxxxx, linux-mm@xxxxxxxxx > > On Fri, Oct 27, 2017 at 11:46:13AM +0200, Dmitry Vyukov wrote: > > On Fri, Oct 27, 2017 at 11:44 AM, syzbot > > <bot+998c483ca801a50e3ce5b63a845216588ada5e2a@xxxxxxxxxxxxxxxxxxxxxxxxx> > > wrote: > > > Hello, > > > > > > syzkaller hit the following crash on > > > a31cc455c512f3f1dd5f79cac8e29a7c8a617af8 > > > git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master > > > compiler: gcc (GCC) 7.1.1 20170620 > > > .config is attached > > > Raw console output is attached. > > > C reproducer is attached > > > syzkaller reproducer is attached. See https://goo.gl/kgGztJ > > > for information about syzkaller reproducers > > > > Andrea or Pavel, can one of you please fix this? It's another use-after-free > related to userfaultfd "fork events", and it can easily be triggered by an > unprivileged user. It was reported a month ago already; the original report is > here: https://groups.google.com/forum/#!topic/syzkaller-bugs/sS99S-Z-9No. > (Please consider adding yourself and/or linux-mm to the MAINTAINERS file for > fs/userfaultfd.c, so that you are Cc'ed on userfaultfd bug reports.) In > userfaultfd_event_wait_completion(), called from dup_fctx(), the kernel is > freeing the the new userfaultfd_ctx because the old one had all its fd's closed, > but actually the new one is still in use by the new mm_struct. > Fixed now: #syz fix: userfaultfd: clear the vma->vm_userfaultfd_ctx if UFFD_EVENT_FORK fails
