Date:   Thu, 28 Feb 2019 10:27:22 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        syzbot <syzbot+2cd2887ea471ed6e6995@...kaller.appspotmail.com>,
        Dan Williams <dan.j.williams@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, Michal Hocko <mhocko@...e.com>,
        nborisov@...e.com, Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Mike Kravetz <kravetz@...ibm.com>
Subject: Re: BUG: Bad page state (5)

On Thu, Feb 28, 2019 at 10:31:53AM +0100, 'Dmitry Vyukov' via syzkaller-bugs wrote:
> On Thu, Feb 28, 2019 at 8:59 AM Eric Biggers <ebiggers@...nel.org> wrote:
> >
> > On Thu, Feb 28, 2019 at 07:53:09AM +0100, 'Dmitry Vyukov' via syzkaller-bugs wrote:
> > > On Wed, Feb 27, 2019 at 9:53 PM Eric Biggers <ebiggers@...nel.org> wrote:
> > > >
> > > > On Tue, Feb 26, 2019 at 10:21:30AM -0800, Eric Biggers wrote:
> > > > > On Wed, Feb 13, 2019 at 12:23:31PM -0800, Andrew Morton wrote:
> > > > > > On Wed, 13 Feb 2019 09:56:04 -0800 syzbot <syzbot+2cd2887ea471ed6e6995@...kaller.appspotmail.com> wrote:
> > > > > >
> > > > > > > Hello,
> > > > > > >
> > > > > > > syzbot found the following crash on:
> > > > > > >
> > > > > > > HEAD commit:    c4f3ef3eb53f Add linux-next specific files for 20190213
> > > > > > > git tree:       linux-next
> > > > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=1130a124c00000
> > > > > > > kernel config:  https://syzkaller.appspot.com/x/.config?x=9ec67976eb2df882
> > > > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=2cd2887ea471ed6e6995
> > > > > > > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > > > > > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14ecdaa8c00000
> > > > > > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12ebe178c00000
> > > > > > >
> > > > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > > > > > > Reported-by: syzbot+2cd2887ea471ed6e6995@...kaller.appspotmail.com
> > > > > >
> > > > > > It looks like a a memfd page was freed with a non-NULL ->mapping.
> > > > > >
> > > > > > Joel touched the memfd code with "mm/memfd: add an F_SEAL_FUTURE_WRITE
> > > > > > seal to memfd" but it would be surprising if syzbot tickled that code?
> > > > > >
> > > > > >
> > > > > > > BUG: Bad page state in process udevd  pfn:472f0
> > > > > > > name:"memfd:"
> > > > > > > page:ffffea00011cbc00 count:0 mapcount:0 mapping:ffff88800df2ad40 index:0xf
> > > > > > > shmem_aops
> > > > > > > flags: 0x1fffc000008000c(uptodate|dirty|swapbacked)
> > > > > > > raw: 01fffc000008000c ffffea0000ac4f08 ffff8880a85af890 ffff88800df2ad40
> > > > > > > raw: 000000000000000f 0000000000000000 00000000ffffffff 0000000000000000
> > > > > > > page dumped because: non-NULL mapping
> > > > > > > Modules linked in:
> > > > > > > CPU: 1 PID: 7586 Comm: udevd Not tainted 5.0.0-rc6-next-20190213 #34
> > > > > > > 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+0x172/0x1f0 lib/dump_stack.c:113
> > > > > > >   bad_page.cold+0xda/0xff mm/page_alloc.c:586
> > > > > > >   free_pages_check_bad+0x142/0x1a0 mm/page_alloc.c:1014
> > > > > > >   free_pages_check mm/page_alloc.c:1023 [inline]
> > > > > > >   free_pages_prepare mm/page_alloc.c:1113 [inline]
> > > > > > >   free_pcp_prepare mm/page_alloc.c:1138 [inline]
> > > > > > >   free_unref_page_prepare mm/page_alloc.c:2991 [inline]
> > > > > > >   free_unref_page_list+0x31d/0xc40 mm/page_alloc.c:3060
> > > > > > > name:"memfd:"
> > > > > > >   release_pages+0x60d/0x1940 mm/swap.c:791
> > > > > > >   pagevec_lru_move_fn+0x218/0x2a0 mm/swap.c:213
> > > > > > >   __pagevec_lru_add mm/swap.c:917 [inline]
> > > > > > >   lru_add_drain_cpu+0x2f7/0x520 mm/swap.c:581
> > > > > > >   lru_add_drain+0x20/0x60 mm/swap.c:652
> > > > > > >   exit_mmap+0x290/0x530 mm/mmap.c:3134
> > > > > > >   __mmput kernel/fork.c:1047 [inline]
> > > > > > >   mmput+0x15f/0x4c0 kernel/fork.c:1068
> > > > > > >   exec_mmap fs/exec.c:1046 [inline]
> > > > > > >   flush_old_exec+0x8d9/0x1c20 fs/exec.c:1279
> > > > > > >   load_elf_binary+0x9bc/0x53f0 fs/binfmt_elf.c:864
> > > > > > >   search_binary_handler fs/exec.c:1656 [inline]
> > > > > > >   search_binary_handler+0x17f/0x570 fs/exec.c:1634
> > > > > > >   exec_binprm fs/exec.c:1698 [inline]
> > > > > > >   __do_execve_file.isra.0+0x1394/0x23f0 fs/exec.c:1818
> > > > > > >   do_execveat_common fs/exec.c:1865 [inline]
> > > > > > >   do_execve fs/exec.c:1882 [inline]
> > > > > > >   __do_sys_execve fs/exec.c:1958 [inline]
> > > > > > >   __se_sys_execve fs/exec.c:1953 [inline]
> > > > > > >   __x64_sys_execve+0x8f/0xc0 fs/exec.c:1953
> > > > > > >   do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
> > > > > > >   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > > > > > > RIP: 0033:0x7fc7001ba207
> > > > > > > Code: Bad RIP value.
> > > > > > > RSP: 002b:00007ffe06aa13b8 EFLAGS: 00000206 ORIG_RAX: 000000000000003b
> > > > > > > RAX: ffffffffffffffda RBX: 00000000ffffffff RCX: 00007fc7001ba207
> > > > > > > RDX: 0000000001fd5fd0 RSI: 00007ffe06aa14b0 RDI: 00007ffe06aa24c0
> > > > > > > RBP: 0000000000625500 R08: 0000000000001c49 R09: 0000000000001c49
> > > > > > > R10: 0000000000000000 R11: 0000000000000206 R12: 0000000001fd5fd0
> > > > > > > R13: 0000000000000007 R14: 0000000001fc6250 R15: 0000000000000005
> > > > > > > BUG: Bad page state in process udevd  pfn:2b13c
> > > > > > > page:ffffea0000ac4f00 count:0 mapcount:0 mapping:ffff88800df2ad40 index:0xe
> > > > > > > shmem_aops
> > > > > > > flags: 0x1fffc000008000c(uptodate|dirty|swapbacked)
> > > > > > > raw: 01fffc000008000c ffff8880a85af890 ffff8880a85af890 ffff88800df2ad40
> > > > > > > raw: 000000000000000e 0000000000000000 00000000ffffffff 0000000000000000
> > > > > > > page dumped because: non-NULL mapping
> > > > > > > Modules linked in:
> > > > > > > CPU: 1 PID: 7586 Comm: udevd Tainted: G    B
> > > > > > > 5.0.0-rc6-next-20190213 #34
> > > > > > > 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+0x172/0x1f0 lib/dump_stack.c:113
> > > > > > >   bad_page.cold+0xda/0xff mm/page_alloc.c:586
> > > > > > > name:"memfd:"
> > > > > > >   free_pages_check_bad+0x142/0x1a0 mm/page_alloc.c:1014
> > > > > > >   free_pages_check mm/page_alloc.c:1023 [inline]
> > > > > > >   free_pages_prepare mm/page_alloc.c:1113 [inline]
> > > > > > >   free_pcp_prepare mm/page_alloc.c:1138 [inline]
> > > > > > >   free_unref_page_prepare mm/page_alloc.c:2991 [inline]
> > > > > > >   free_unref_page_list+0x31d/0xc40 mm/page_alloc.c:3060
> > > > > > >   release_pages+0x60d/0x1940 mm/swap.c:791
> > > > > > >   pagevec_lru_move_fn+0x218/0x2a0 mm/swap.c:213
> > > > > > >   __pagevec_lru_add mm/swap.c:917 [inline]
> > > > > > >   lru_add_drain_cpu+0x2f7/0x520 mm/swap.c:581
> > > > > > >   lru_add_drain+0x20/0x60 mm/swap.c:652
> > > > > > >   exit_mmap+0x290/0x530 mm/mmap.c:3134
> > > > > > >   __mmput kernel/fork.c:1047 [inline]
> > > > > > >   mmput+0x15f/0x4c0 kernel/fork.c:1068
> > > > > > >   exec_mmap fs/exec.c:1046 [inline]
> > > > > > >   flush_old_exec+0x8d9/0x1c20 fs/exec.c:1279
> > > > > > >   load_elf_binary+0x9bc/0x53f0 fs/binfmt_elf.c:864
> > > > > > >   search_binary_handler fs/exec.c:1656 [inline]
> > > > > > >   search_binary_handler+0x17f/0x570 fs/exec.c:1634
> > > > > > >   exec_binprm fs/exec.c:1698 [inline]
> > > > > > >   __do_execve_file.isra.0+0x1394/0x23f0 fs/exec.c:1818
> > > > > > >   do_execveat_common fs/exec.c:1865 [inline]
> > > > > > >   do_execve fs/exec.c:1882 [inline]
> > > > > > >   __do_sys_execve fs/exec.c:1958 [inline]
> > > > > > >   __se_sys_execve fs/exec.c:1953 [inline]
> > > > > > >   __x64_sys_execve+0x8f/0xc0 fs/exec.c:1953
> > > > > > >   do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
> > > > > > >   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > > > > > > RIP: 0033:0x7fc7001ba207
> > > > > > > Code: Bad RIP value.
> > > > > > > RSP: 002b:00007ffe06aa13b8 EFLAGS: 00000206 ORIG_RAX: 000000000000003b
> > > > > > > RAX: ffffffffffffffda RBX: 00000000ffffffff RCX: 00007fc7001ba207
> > > > > > > RDX: 0000000001fd5fd0 RSI: 00007ffe06aa14b0 RDI: 00007ffe06aa24c0
> > > > > > > RBP: 0000000000625500 R08: 0000000000001c49 R09: 0000000000001c49
> > > > > > > R10: 0000000000000000 R11: 0000000000000206 R12: 0000000001fd5fd0
> > > > > > > R13: 0000000000000007 R14: 0000000001fc6250 R15: 0000000000000005
> > > > > > >
> > > > > > >
> > > > > > > ---
> > > > > > > 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
> > > > > >
> > > > >
> > > > > It's apparently the bug in the io_uring patchset I reported yesterday (well, I
> > > > > stole it from another open syzbot bug...) and Jens is already planning to fix:
> > > > > https://marc.info/?l=linux-api&m=155115288114046&w=2.  Reproducer is similar,
> > > > > and the crash bisects down to the same commit from the io_uring patchset:
> > > > > "block: implement bio helper to add iter bvec pages to bio".
> > > > >
> > > >
> > > > Fixed in next-20190227.  The fix was folded into "block: implement bio helper to
> > > > add iter bvec pages to bio".  Telling syzbot to invalidate this bug report:
> > > >
> > > > #syz invalid
> > >
> > > Was this discovered separately? We could also add Reported-by (or
> > > Tested-by) tag to the commit.
> > >
> >
> > My report was based on a crash from the syzbot dashboard.  However, there's no
> > fixing commit, as the fix was folded into the original patch.  I.e. the mainline
> > git history (if/when the io_uring stuff is actually merged) won't show the bug
> > ever being introduced.  Thus Reported-by isn't appropriate, and I used '#syz
> > invalid' instead of '#syz fix'.  Nor did syzbot specifically test the new
> > version of the patch beyond fuzzing the next day's linux-next...  So while I
> > personally might have added an informal note in the commit message, I don't
> > think those formal tags make sense for folded-in linux-next fixes like this.
> 
> This was discussed before and we come to conclusion that Tested-by is
> a reasonable thing in such case:
> https://groups.google.com/d/msg/syzkaller-bugs/xiSF9GdiikU/uBoyYyf3AQAJ
> It did test the patch since it found the bug. Tested-by does not
> necessary mean that the person did all possible kinds of testing on
> all versions, right?
> 

syzbot didn't actually run the reproducer on the new version of the patch; I
did.  And I have high standards so I wouldn't offer my Tested-by just based on
that, as the patch could still have many other problems which I did not test...

Anyway, I don't think you will have much success trying to make people record
the bug fix history of every linux-next patch.  In some branches that go into
linux-next, patches are regularly merged, split, replaced, or dropped.  Also
developers may use a free-form sentence explaining that a fix was folded in, as
e.g. using Reported-by incorrectly implies that the patch fixes an existing bug.

So I think that for linux-next people will sometimes just have to update the
syzbot bug statuses manually.

- Eric

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