BUG: Bad page state (5)

[syzbot]

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+2cd288...@syzkaller.appspotmail.com

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.
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syzbot.
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Andrew Morton]

On Wed, 13 Feb 2019 09:56:04 -0800 syzbot <syzbot+2cd288...@syzkaller.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+2cd288...@syzkaller.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?

[Eric Biggers]

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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".

- Eric

[Eric Biggers]

> 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

- Eric

[Dmitry Vyukov]

Was this discovered separately? We could also add Reported-by (or
Tested-by) tag to the commit.

[Eric Biggers]

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.

- Eric

[Dmitry Vyukov]

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?

[Eric Biggers]

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