Message-ID: <a8ff5d6c-594d-13eb-4b96-2becc8936a4e@iogearbox.net>
Date:   Thu, 11 Jan 2018 11:48:28 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot <syzbot+d85bfb332db8f0794212@...kaller.appspotmail.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, syzkaller-bugs@...glegroups.com
Subject: Re: KASAN: use-after-free Read in __bpf_prog_put

Hi Dmitry,

On 01/11/2018 11:22 AM, Dmitry Vyukov wrote:
> On Thu, Jan 11, 2018 at 11:17 AM, syzbot
> <syzbot+d85bfb332db8f0794212@...kaller.appspotmail.com> wrote:
>> Hello,
>>
>> syzkaller hit the following crash on
>> 4147d50978df60f34d444c647dde9e5b34a4315e
>> git://git.cmpxchg.org/linux-mmots.git/master
>> compiler: gcc (GCC) 7.1.1 20170620
>> .config is attached
>> Raw console output is attached.
>> Unfortunately, I don't have any reproducer for this bug yet.
>>
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+d85bfb332db8f0794212@...kaller.appspotmail.com
>> It will help syzbot understand when the bug is fixed. See footer for
>> details.
>> If you forward the report, please keep this part and the footer.
>>
>> netlink: 3 bytes leftover after parsing attributes in process
>> `syz-executor5'.
>> ==================================================================
>> BUG: KASAN: use-after-free in __bpf_prog_put+0x5e8/0x640
>> kernel/bpf/syscall.c:944
>> netlink: 'syz-executor5': attribute type 5 has an invalid length.
>> Read of size 8 at addr ffff8801d3619658 by task syz-executor0/12398
>>
>> CPU: 1 PID: 12398 Comm: syz-executor0 Not tainted 4.15.0-rc7-mm1+ #53
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>> Google 01/01/2011
>> Call Trace:
>>  __dump_stack lib/dump_stack.c:17 [inline]
>>  dump_stack+0x194/0x257 lib/dump_stack.c:53
>>  print_address_description+0x73/0x250 mm/kasan/report.c:256
>>  kasan_report_error mm/kasan/report.c:354 [inline]
>>  kasan_report+0x23b/0x360 mm/kasan/report.c:412
>>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
>>  __bpf_prog_put+0x5e8/0x640 kernel/bpf/syscall.c:944
>>  bpf_prog_put+0x1a/0x20 kernel/bpf/syscall.c:961
>>  prog_fd_array_put_ptr+0x15/0x20 kernel/bpf/arraymap.c:446
>>  fd_array_map_delete_elem+0xc8/0x110 kernel/bpf/arraymap.c:420
>>  map_delete_elem kernel/bpf/syscall.c:737 [inline]
>>  SYSC_bpf kernel/bpf/syscall.c:1814 [inline]
>>  SyS_bpf+0x22ea/0x4400 kernel/bpf/syscall.c:1782
>>  entry_SYSCALL_64_fastpath+0x29/0xa0
>> RIP: 0033:0x452ac9
>> RSP: 002b:00007fb70df60c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000141
>> RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452ac9
>> RDX: 0000000000000010 RSI: 0000000020f02ff0 RDI: 0000000000000003
>> RBP: 00000000000003aa R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f3890
>> R13: 00000000ffffffff R14: 00007fb70df616d4 R15: 0000000000000000
>>
>> Allocated by task 11996:
>>  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>>  set_track mm/kasan/kasan.c:459 [inline]
>>  kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:552
>>  kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
>>  kmem_cache_alloc+0x12e/0x760 mm/slab.c:3541
>>  kmem_cache_zalloc include/linux/slab.h:694 [inline]
>>  get_empty_filp+0xfb/0x4f0 fs/file_table.c:122
>>  path_openat+0xed/0x3530 fs/namei.c:3514
>>  do_filp_open+0x25b/0x3b0 fs/namei.c:3572
>>  do_sys_open+0x502/0x6d0 fs/open.c:1059
>>  SYSC_open fs/open.c:1077 [inline]
>>  SyS_open+0x2d/0x40 fs/open.c:1072
>>  entry_SYSCALL_64_fastpath+0x29/0xa0
>>
>> Freed by task 11994:
>>  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>>  set_track mm/kasan/kasan.c:459 [inline]
>>  __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
>>  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
>>  __cache_free mm/slab.c:3485 [inline]
>>  kmem_cache_free+0x86/0x2b0 mm/slab.c:3743
>>  file_free_rcu+0x5c/0x70 fs/file_table.c:49
>>  __rcu_reclaim kernel/rcu/rcu.h:172 [inline]
>>  rcu_do_batch kernel/rcu/tree.c:2675 [inline]
>>  invoke_rcu_callbacks kernel/rcu/tree.c:2934 [inline]
>>  __rcu_process_callbacks kernel/rcu/tree.c:2901 [inline]
>>  rcu_process_callbacks+0xd6c/0x17f0 kernel/rcu/tree.c:2918
>>  __do_softirq+0x2d7/0xb85 kernel/softirq.c:285
>>
>> The buggy address belongs to the object at ffff8801d36195c0
>>  which belongs to the cache filp of size 456
>> The buggy address is located 152 bytes inside of
>>  456-byte region [ffff8801d36195c0, ffff8801d3619788)
>> The buggy address belongs to the page:
>> page:ffffea00074d8640 count:1 mapcount:0 mapping:ffff8801d36190c0 index:0x0
>> flags: 0x2fffc0000000100(slab)
>> raw: 02fffc0000000100 ffff8801d36190c0 0000000000000000 0000000100000006
>> raw: ffffea00074c49a0 ffffea000747a160 ffff8801dae30180 0000000000000000
>> page dumped because: kasan: bad access detected
>>
>> Memory state around the buggy address:
>>  ffff8801d3619500: fb fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>  ffff8801d3619580: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
>>>
>>> ffff8801d3619600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>
>>                                                     ^
>>  ffff8801d3619680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>  ffff8801d3619700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ==================================================================
> 
> 
> Is it the same as "general protection fault in __bpf_prog_put"?
> https://groups.google.com/forum/#!topic/syzkaller-bugs/jUsNMmVgms0
> 
> The first stack looks similar, but alloc/free stacks looks unrelated.
> What's the root cause of this? Is prog->aux an uninitialized pointer?
> I wonder if initializing memory in kmalloc would help to prevent this
> bug from duplicating? E.g. if we init memory to 0, it would always
> cause GPFs, or if we init to an invalid pointer, always cause a bad
> paging fault. Is it's the case, then I think we should do it to reduce
> number of failure modes and syzbot reports.

This one in bpf tree fixes it:

https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/commit/?id=bbeb6e4323dad9b5e0ee9f60c223dd532e2403b1

Despite this one not having a reproducer, I'm pretty certain it's very
much related to all the ones coming in yesterday (which the above fixes).

>> This bug is generated by a dumb bot. It may contain errors.
>> See https://goo.gl/tpsmEJ for details.
>> Direct all questions to syzkaller@...glegroups.com.
>>
>> syzbot will keep track of this bug report.
>> If you forgot to add the Reported-by tag, once the fix for this bug is
>> merged
>> into any tree, please reply to this email with:
>> #syz fix: exact-commit-title
>> To mark this as a duplicate of another syzbot report, please reply with:
>> #syz dup: exact-subject-of-another-report
>> If it's a one-off invalid bug report, please reply with:
>> #syz invalid
>> Note: if the crash happens again, it will cause creation of a new bug
>> report.
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>>
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