Message-ID: <CAG_fn=UjeL9BmAq+FDK01n4mH7ieQXpxkRRxAbDPd5UcC7eZPw@mail.gmail.com>
Date:   Wed, 19 Dec 2018 11:23:39 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>, bart.vanassche@....com,
        axboe@...nel.dk, matias.bjorling@....com
Cc:     Andi Kleen <ak@...ux.intel.com>, jack@...e.cz, jlayton@...hat.com,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        mawilcox@...rosoft.com, mgorman@...hsingularity.net,
        syzkaller-bugs@...glegroups.com
Subject: Re: KMSAN: kernel-infoleak in copy_page_to_iter (2)

On Thu, Sep 13, 2018 at 11:23 AM Alexander Potapenko <glider@...gle.com> wrote:
>
> On Thu, Sep 13, 2018 at 11:18 AM syzbot
> <syzbot+2dcfeaf8cb49b05e8f1a@...kaller.appspotmail.com> 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@...kaller.appspotmail.com
> >
> > 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.
> > ---
> > This bug is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@...glegroups.com.
> >
> > syzbot will keep track of this bug report. See:
> > https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> > syzbot.
> > syzbot can test patches for this bug, for details see:
> > https://goo.gl/tpsmEJ#testing-patches
> >
> > --
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> > To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/00000000000016eb330575bd2fab%40google.com.
> > For more options, visit https://groups.google.com/d/optout.
>
>
>
> --
> Alexander Potapenko
> Software Engineer
>
> Google Germany GmbH
> Erika-Mann-Straße, 33
> 80636 München
>
> Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg



-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

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

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