On Tue, Dec 17, 2019 at 10:38:09PM +0000, Catalin Marinas wrote: > On Tue, Dec 17, 2019 at 04:57:34PM +0100, Magnus Karlsson wrote: > > On Tue, Dec 17, 2019 at 4:40 PM Catalin Marinas <catalin.marinas@xxxxxxx> wrote: > > > On Tue, Dec 17, 2019 at 02:27:22PM +0100, Magnus Karlsson wrote: > > > > On Mon, Dec 16, 2019 at 4:10 PM Magnus Karlsson > > > > <magnus.karlsson@xxxxxxxxx> wrote: > > > > > On Mon, Dec 16, 2019 at 4:00 PM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote: > > > > > > On Sat, Dec 14, 2019 at 08:20:07AM -0800, syzbot wrote: > > > > > > > syzbot has found a reproducer for the following crash on: > > > > > > > > > > > > > > HEAD commit: 1d1997db Revert "nfp: abm: fix memory leak in nfp_abm_u32_.. > > > > > > > git tree: net-next > > > > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=1029f851e00000 > > > > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=cef1fd5032faee91 > > > > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=9301f2f33873407d5b33 > > > > > > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > > > > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=119d9fb1e00000 > > > > > > > > > > > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > > > > > > Reported-by: syzbot+9301f2f33873407d5b33@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > > > > > > > Bjorn / Magnus, given xsk below, PTAL, thanks! > > > > > > > > > > Thanks. I will take a look at it right away. > > > > > > > > > > /Magnus > > > > > > > > After looking through the syzcaller report, I have the following > > > > hypothesis that would dearly need some comments from MM-savy people > > > > out there. Syzcaller creates, using mmap, a memory area that is > > > > > > I guess that's not an anonymous mmap() since we don't seem to have a > > > struct page for src in cow_user_page() (the WARN_ON_ONCE path). Do you > > > have more information on the mmap() call? > > > > I have this from the syzcaller logs: > > > > mmap(&(0x7f0000001000/0x2000)=nil, 0x2000, 0xfffffe, 0x12, r8, 0x0) > > getsockopt$XDP_MMAP_OFFSETS(r8, 0x11b, 0x7, &(0x7f0000001300), > > &(0x7f0000000100)=0x60) > > > > The full log can be found at: > > https://syzkaller.appspot.com/x/repro.syz?x=119d9fb1e00000 > > Thanks. Prior to mmap, we have: > > r8 = socket$xdp(0x2c, 0x3, 0x0) > > So basically we have an mmap() on a socket descriptor with a subsequent > copy_to_user() writing this range. We do we even end up doing CoW on > such mapping? It's a non-readable private mapping of a socket. Any write to it would cause CoW. BTW, how useful memory mapped sockets are? I don't know much about networking, but it looks like a rarely used feature that substantially increase attack surface. CAP_NET_RAW is easy to come by nowadays with user-ns. Few years back I was able to modify zero page via memory mapped socket... > Maybe the socket code should also implement the .fault() > file op. It needs more digging. Caller definitely does a weird thing here that doesn't suppose to produce a meaningful result. I think we can keep the warning for now just to make sure we don't have any more-or-less legitimate obscure use-case. But ultimately this WARN_ON_ONCE() has to be upgraded to SIGSEGV or SIGBUS. Pretending that we do anything meaningful here by clearing the page unlikely does anything useful to a user. -- Kirill A. Shutemov
