Messages in this thread | | | From | Björn Töpel <> | Date | Sun, 10 Jun 2018 15:03:14 +0200 | Subject | Re: WARNING: kmalloc bug in xdp_umem_create |
| |
Den sön 10 juni 2018 kl 14:53 skrev Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>: > > On 2018/06/10 20:52, Dmitry Vyukov wrote: > > On Sun, Jun 10, 2018 at 11:31 AM, Björn Töpel <bjorn.topel@gmail.com> wrote: > >> Den sön 10 juni 2018 kl 04:53 skrev Tetsuo Handa > >> <penguin-kernel@i-love.sakura.ne.jp>: > >>> > >>> On 2018/06/10 7:47, syzbot wrote: > >>>> Hello, > >>>> > >>>> syzbot found the following crash on: > >>>> > >>>> HEAD commit: 7d3bf613e99a Merge tag 'libnvdimm-for-4.18' of git://git.k.. > >>>> git tree: upstream > >>>> console output: https://syzkaller.appspot.com/x/log.txt?x=1073f68f800000 > >>>> kernel config: https://syzkaller.appspot.com/x/.config?x=f04d8d0a2afb789a > >>>> dashboard link: https://syzkaller.appspot.com/bug?extid=4abadc5d69117b346506 > >>>> compiler: gcc (GCC) 8.0.1 20180413 (experimental) > >>>> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=13c9756f800000 > >>>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16366f9f800000 > >>>> > >>>> IMPORTANT: if you fix the bug, please add the following tag to the commit: > >>>> Reported-by: syzbot+4abadc5d69117b346506@syzkaller.appspotmail.com > >>>> > >>>> random: sshd: uninitialized urandom read (32 bytes read) > >>>> random: sshd: uninitialized urandom read (32 bytes read) > >>>> random: sshd: uninitialized urandom read (32 bytes read) > >>>> random: sshd: uninitialized urandom read (32 bytes read) > >>>> random: sshd: uninitialized urandom read (32 bytes read) > >>>> WARNING: CPU: 1 PID: 4537 at mm/slab_common.c:996 kmalloc_slab+0x56/0x70 mm/slab_common.c:996 > >>>> Kernel panic - not syncing: panic_on_warn set ... > >>> > >>> syzbot gave up upon kmalloc(), but actually error handling path has > >>> NULL pointer dereference bug. > >>> > >> > >> Thanks Tetsuo! This crash has been fixed by Daniel Borkmann in commit > >> c09290c56376 ("bpf, xdp: fix crash in xdp_umem_unaccount_pages"). > > > > Let's tell syzbot about this: > > > > #syz fix: bpf, xdp: fix crash in xdp_umem_unaccount_pages > > > > > Excuse me, but that patch fixes NULL pointer dereference which occurs after kmalloc()'s > "WARNING: CPU: 1 PID: 4537 at mm/slab_common.c:996 kmalloc_slab+0x56/0x70 mm/slab_common.c:996" > message. That is, "Too large memory allocation" itself is not yet fixed.
The code relies on that the sl{u,a,o}b layer says no, and the setsockopt bails out. The warning could be opted out using __GFP_NOWARN. Is there another preferred way? Two get_user_pages calls, where the first call would set pages to NULL just to fault the region? Walk the process' VMAs? Something else?
Björn
| |