Re: KMSAN: kernel-infoleak in copy_page_to_iter (2)

[Alexander Potapenko]

From: Alexander Potapenko <glider@xxxxxxxxxx>
Date: Wed, Jan 2, 2019 at 11:09 AM
To: Jens Axboe
Cc: Andrew Morton, <bart.vanassche@xxxxxxx>,
<matias.bjorling@xxxxxxx>, Andi Kleen, <jack@xxxxxxx>,
<jlayton@xxxxxxxxxx>, LKML, Linux Memory Management List,
<mawilcox@xxxxxxxxxxxxx>, <mgorman@xxxxxxxxxxxxxxxxxxx>,
<syzkaller-bugs@xxxxxxxxxxxxxxxx>

> On Wed, Dec 19, 2018 at 2:23 PM Jens Axboe <axboe@xxxxxxxxx> wrote:
> >
> > On 12/19/18 3:23 AM, Alexander Potapenko wrote:
> > > On Thu, Sep 13, 2018 at 11:23 AM Alexander Potapenko <glider@xxxxxxxxxx> wrote:
> > >>
> > >> On Thu, Sep 13, 2018 at 11:18 AM syzbot
> > >> <syzbot+2dcfeaf8cb49b05e8f1a@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> > >>>
> > >>> Hello,
> > >>>
> > >>> syzbot found the following crash on:
> > >>>
> > >>> HEAD commit:    123906095e30 kmsan: introduce kmsan_interrupt_enter()/kmsa..
> > >>> git tree:       https://github.com/google/kmsan.git/master
> > >>> console output: https://syzkaller.appspot.com/x/log.txt?x=1249fcb8400000
> > >>> kernel config:  https://syzkaller.appspot.com/x/.config?x=848e40757852af3e
> > >>> dashboard link: https://syzkaller.appspot.com/bug?extid=2dcfeaf8cb49b05e8f1a
> > >>> compiler:       clang version 7.0.0 (trunk 334104)
> > >>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=116ef050400000
> > >>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=122870ff800000
> > >>>
> > >>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > >>> Reported-by: syzbot+2dcfeaf8cb49b05e8f1a@xxxxxxxxxxxxxxxxxxxxxxxxx
> > >>>
> > >>> random: sshd: uninitialized urandom read (32 bytes read)
> > >>> ==================================================================
> > >>> BUG: KMSAN: kernel-infoleak in copyout lib/iov_iter.c:140 [inline]
> > >>> BUG: KMSAN: kernel-infoleak in copy_page_to_iter_iovec lib/iov_iter.c:212
> > >>> [inline]
> > >>> BUG: KMSAN: kernel-infoleak in copy_page_to_iter+0x754/0x1b70
> > >>> lib/iov_iter.c:716
> > >>> CPU: 0 PID: 4516 Comm: blkid Not tainted 4.17.0+ #9
> > >>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > >>> Google 01/01/2011
> > >>> Call Trace:
> > >>>   __dump_stack lib/dump_stack.c:77 [inline]
> > >>>   dump_stack+0x185/0x1d0 lib/dump_stack.c:113
> > >>>   kmsan_report+0x188/0x2a0 mm/kmsan/kmsan.c:1125
> > >>>   kmsan_internal_check_memory+0x17e/0x1f0 mm/kmsan/kmsan.c:1238
> > >>>   kmsan_copy_to_user+0x7a/0x160 mm/kmsan/kmsan.c:1261
> > >>>   copyout lib/iov_iter.c:140 [inline]
> > >>>   copy_page_to_iter_iovec lib/iov_iter.c:212 [inline]
> > >>>   copy_page_to_iter+0x754/0x1b70 lib/iov_iter.c:716
> > >>>   generic_file_buffered_read mm/filemap.c:2185 [inline]
> > >>>   generic_file_read_iter+0x2ef8/0x44d0 mm/filemap.c:2362
> > >>>   blkdev_read_iter+0x20d/0x280 fs/block_dev.c:1930
> > >>>   call_read_iter include/linux/fs.h:1778 [inline]
> > >>>   new_sync_read fs/read_write.c:406 [inline]
> > >>>   __vfs_read+0x775/0x9d0 fs/read_write.c:418
> > >>>   vfs_read+0x36c/0x6b0 fs/read_write.c:452
> > >>>   ksys_read fs/read_write.c:578 [inline]
> > >>>   __do_sys_read fs/read_write.c:588 [inline]
> > >>>   __se_sys_read fs/read_write.c:586 [inline]
> > >>>   __x64_sys_read+0x1bf/0x3e0 fs/read_write.c:586
> > >>>   do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:287
> > >>>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > >>> RIP: 0033:0x7fdeff68f310
> > >>> RSP: 002b:00007ffe999660b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
> > >>> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fdeff68f310
> > >>> RDX: 0000000000000100 RSI: 0000000001e78df8 RDI: 0000000000000003
> > >>> RBP: 0000000001e78dd0 R08: 0000000000000028 R09: 0000000001680000
> > >>> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000001e78030
> > >>> R13: 0000000000000100 R14: 0000000001e78080 R15: 0000000001e78de8
> > >>>
> > >>> Uninit was created at:
> > >>>   kmsan_save_stack_with_flags mm/kmsan/kmsan.c:282 [inline]
> > >>>   kmsan_alloc_meta_for_pages+0x161/0x3a0 mm/kmsan/kmsan.c:819
> > >>>   kmsan_alloc_page+0x82/0xe0 mm/kmsan/kmsan.c:889
> > >>>   __alloc_pages_nodemask+0xf7b/0x5cc0 mm/page_alloc.c:4402
> > >>>   alloc_pages_current+0x6b1/0x970 mm/mempolicy.c:2093
> > >>>   alloc_pages include/linux/gfp.h:494 [inline]
> > >>>   __page_cache_alloc+0x95/0x320 mm/filemap.c:946
> > >>>   pagecache_get_page+0x52b/0x1450 mm/filemap.c:1577
> > >>>   grab_cache_page_write_begin+0x10d/0x190 mm/filemap.c:3089
> > >>>   block_write_begin+0xf9/0x3a0 fs/buffer.c:2068
> > >>>   blkdev_write_begin+0xf5/0x110 fs/block_dev.c:584
> > >>>   generic_perform_write+0x438/0x9d0 mm/filemap.c:3139
> > >>>   __generic_file_write_iter+0x43b/0xa10 mm/filemap.c:3264
> > >>>   blkdev_write_iter+0x3a8/0x5f0 fs/block_dev.c:1910
> > >>>   do_iter_readv_writev+0x81c/0xa20 include/linux/fs.h:1778
> > >>>   do_iter_write+0x30d/0xd50 fs/read_write.c:959
> > >>>   vfs_writev fs/read_write.c:1004 [inline]
> > >>>   do_writev+0x3be/0x820 fs/read_write.c:1039
> > >>>   __do_sys_writev fs/read_write.c:1112 [inline]
> > >>>   __se_sys_writev fs/read_write.c:1109 [inline]
> > >>>   __x64_sys_writev+0xe1/0x120 fs/read_write.c:1109
> > >>>   do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:287
> > >>>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > >>>
> > >>> Bytes 4-255 of 256 are uninitialized
> > >>> Memory access starts at ffff8801b9903000
> > >>> ==================================================================
> > >> This particular report was caused by the repro program writing a byte
> > >> to /dev/nullb0 and /sbin/blkid reading from that device in the
> > >> background.
> > >> But it turns out that simply running `cat /dev/nullb0` already prints
> > >> uninitialized kernel memory.
> > >> Is this the intended behavior of the null block driver?
> > > A friendly ping, this bug is still reproducible on syzbot.
> >
> > Does this fix it?
> There must be something wrong with my tool, as it stops reporting this
> bug when I apply your patch.
> However when I run `cat /dev/nullb0 | strings` and wait long enough I
> start seeing meaningful strings (file names, env dumps etc.)
> I suspect this is still unexpected, right?
A friendly ping, as we're still seeing similar errors.
> > diff --git a/drivers/block/null_blk_main.c b/drivers/block/null_blk_main.c
> > index 62c9654b9ce8..08808c572692 100644
> > --- a/drivers/block/null_blk_main.c
> > +++ b/drivers/block/null_blk_main.c
> > @@ -655,7 +655,7 @@ static struct nullb_page *null_alloc_page(gfp_t gfp_flags)
> >         if (!t_page)
> >                 goto out;
> >
> > -       t_page->page = alloc_pages(gfp_flags, 0);
> > +       t_page->page = alloc_pages(gfp_flags | __GFP_ZERO, 0);
> >         if (!t_page->page)
> >                 goto out_freepage;
> >
> >
> > --
> > Jens Axboe
> >
>
>
> --
> Alexander Potapenko
> Software Engineer
>
> Google Germany GmbH
> Erika-Mann-StraÃe, 33
> 80636 MÃnchen
>
> GeschÃftsfÃhrer: Paul Manicle, Halimah DeLaine Prado
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg



-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-StraÃe, 33
80636 MÃnchen

GeschÃftsfÃhrer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg