On Mon, Jul 9, 2018 at 12:48 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > On Mon, Jul 9, 2018 at 12:15 PM, Kirill A. Shutemov > <kirill@xxxxxxxxxxxxx> wrote: >> On Sun, Jul 08, 2018 at 10:51:03PM -0700, syzbot wrote: >>> Hello, >>> >>> syzbot found the following crash on: >>> >>> HEAD commit: b2d44d145d2a Merge tag '4.18-rc3-smb3fixes' of git://git.s.. >>> git tree: upstream >>> console output: https://syzkaller.appspot.com/x/log.txt?x=11d07748400000 >>> kernel config: https://syzkaller.appspot.com/x/.config?x=2ca6c7a31d407f86 >>> dashboard link: https://syzkaller.appspot.com/bug?extid=3f84280d52be9b7083cc >>> compiler: gcc (GCC) 8.0.1 20180413 (experimental) >>> >>> Unfortunately, I don't have any reproducer for this crash yet. >>> >>> IMPORTANT: if you fix the bug, please add the following tag to the commit: >>> Reported-by: syzbot+3f84280d52be9b7083cc@xxxxxxxxxxxxxxxxxxxxxxxxx >>> >>> next ffff8801ce5e7040 prev ffff8801d20eca50 mm ffff88019c1e13c0 >>> prot 27 anon_vma ffff88019680cdd8 vm_ops 0000000000000000 >>> pgoff 0 file ffff8801b2ec2d00 private_data 0000000000000000 >>> flags: 0xff(read|write|exec|shared|mayread|maywrite|mayexec|mayshare) >>> ------------[ cut here ]------------ >>> kernel BUG at mm/memory.c:1422! >> >> Looks like vma_is_anonymous() false-positive. >> >> Any clues what file is it? I would guess some kind of socket, but it's not >> clear from log which exactly. > > > From the log it looks like it was this program (number 3 matches Comm: > syz-executor3): > > 08:39:32 executing program 3: > r0 = socket$nl_route(0x10, 0x3, 0x0) > bind$netlink(r0, &(0x7f00000002c0)={0x10, 0x0, 0x0, 0x100000}, 0xc) > getsockname(r0, &(0x7f0000000000)=@pppol2tpv3in6={0x0, 0x0, {0x0, > <r1=>0xffffffffffffffff, 0x0, 0x0, 0x0, 0x0, {0x0, 0x0, 0x0, > @loopback}}}, &(0x7f00000000c0)=0x3a) > mmap(&(0x7f0000e00000/0x200000)=nil, 0x200000, 0x7fdff, 0x11, r1, 0x0) > ioctl$FIBMAP(r0, 0x1, &(0x7f0000000100)=0x9) > r2 = socket$inet6(0xa, 0x1000000000002, 0x0) > ioctl(r2, 0x8912, &(0x7f00000001c0)="796d05ad441e829115ac7fd77200") > r3 = syz_open_dev$vcsa(&(0x7f0000000140)='/dev/vcsa#\x00', 0x3, 0x2) > ioctl$VHOST_SET_VRING_ENDIAN(r3, 0x4008af13, &(0x7f0000000180)={0x0, 0x8}) > sendto$inet(0xffffffffffffffff, &(0x7f0000a88f88), 0xffffffffffffff31, > 0x0, &(0x7f0000e68000)={0x2, 0x0, @multicast2=0xe0000002}, > 0xfffffffffffffeb3) > ftruncate(r1, 0x6) > mmap(&(0x7f0000e00000/0x200000)=nil, 0x200000, 0x0, 0x11, r0, 0x0) > setsockopt$SO_TIMESTAMPING(r1, 0x1, 0x25, &(0x7f0000000080)=0x804, 0x4) > > But take what happens here with a grain of salt, it can pretend that > it's doing one thing, but actually do something different. > So that r1 passed to ftruncate is something that getsockname returned > somewhere in the middle of address. And since the socket is not > actually ppp, it can be just some bytes in the middle of netlink > address, that than happened to be small and match some existing fd... This also happened only once so far: https://syzkaller.appspot.com/bug?extid=3f84280d52be9b7083cc and I can't reproduce it rerunning this program. So it's either a very subtle race, or fd in the middle of netlink address magically matched some fd once, or something else...
