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Date: Tue, 10 Apr 2018 09:04:45 -0700
From: Yonghong Song <yhs@...com>
To: Daniel Borkmann <daniel@...earbox.net>, <ast@...com>,
<netdev@...r.kernel.org>
CC: <kernel-team@...com>
Subject: Re: [PATCH bpf v3] bpf/tracing: fix a deadlock in
perf_event_detach_bpf_prog
On 4/10/18 1:54 AM, Daniel Borkmann wrote:
> On 04/10/2018 09:21 AM, Yonghong Song wrote:
>> syzbot reported a possible deadlock in perf_event_detach_bpf_prog.
>> The error details:
>> ======================================================
>> WARNING: possible circular locking dependency detected
>> 4.16.0-rc7+ #3 Not tainted
>> ------------------------------------------------------
>> syz-executor7/24531 is trying to acquire lock:
>> (bpf_event_mutex){+.+.}, at: [<000000008a849b07>] perf_event_detach_bpf_prog+0x92/0x3d0 kernel/trace/bpf_trace.c:854
>>
>> but task is already holding lock:
>> (&mm->mmap_sem){++++}, at: [<0000000038768f87>] vm_mmap_pgoff+0x198/0x280 mm/util.c:353
>>
>> which lock already depends on the new lock.
>>
>> the existing dependency chain (in reverse order) is:
>>
>> -> #1 (&mm->mmap_sem){++++}:
>> __might_fault+0x13a/0x1d0 mm/memory.c:4571
>> _copy_to_user+0x2c/0xc0 lib/usercopy.c:25
>> copy_to_user include/linux/uaccess.h:155 [inline]
>> bpf_prog_array_copy_info+0xf2/0x1c0 kernel/bpf/core.c:1694
>> perf_event_query_prog_array+0x1c7/0x2c0 kernel/trace/bpf_trace.c:891
>> _perf_ioctl kernel/events/core.c:4750 [inline]
>> perf_ioctl+0x3e1/0x1480 kernel/events/core.c:4770
>> vfs_ioctl fs/ioctl.c:46 [inline]
>> do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
>> SYSC_ioctl fs/ioctl.c:701 [inline]
>> SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
>> do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
>> entry_SYSCALL_64_after_hwframe+0x42/0xb7
>>
>> -> #0 (bpf_event_mutex){+.+.}:
>> lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3920
>> __mutex_lock_common kernel/locking/mutex.c:756 [inline]
>> __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893
>> mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
>> perf_event_detach_bpf_prog+0x92/0x3d0 kernel/trace/bpf_trace.c:854
>> perf_event_free_bpf_prog kernel/events/core.c:8147 [inline]
>> _free_event+0xbdb/0x10f0 kernel/events/core.c:4116
>> put_event+0x24/0x30 kernel/events/core.c:4204
>> perf_mmap_close+0x60d/0x1010 kernel/events/core.c:5172
>> remove_vma+0xb4/0x1b0 mm/mmap.c:172
>> remove_vma_list mm/mmap.c:2490 [inline]
>> do_munmap+0x82a/0xdf0 mm/mmap.c:2731
>> mmap_region+0x59e/0x15a0 mm/mmap.c:1646
>> do_mmap+0x6c0/0xe00 mm/mmap.c:1483
>> do_mmap_pgoff include/linux/mm.h:2223 [inline]
>> vm_mmap_pgoff+0x1de/0x280 mm/util.c:355
>> SYSC_mmap_pgoff mm/mmap.c:1533 [inline]
>> SyS_mmap_pgoff+0x462/0x5f0 mm/mmap.c:1491
>> SYSC_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
>> SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:91
>> do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
>> entry_SYSCALL_64_after_hwframe+0x42/0xb7
>>
>> other info that might help us debug this:
>>
>> Possible unsafe locking scenario:
>>
>> CPU0 CPU1
>> ---- ----
>> lock(&mm->mmap_sem);
>> lock(bpf_event_mutex);
>> lock(&mm->mmap_sem);
>> lock(bpf_event_mutex);
>>
>> *** DEADLOCK ***
>> ======================================================
>>
>> The bug is introduced by Commit f371b304f12e ("bpf/tracing: allow
>> user space to query prog array on the same tp") where copy_to_user,
>> which requires mm->mmap_sem, is called inside bpf_event_mutex lock.
>> At the same time, during perf_event file descriptor close,
>> mm->mmap_sem is held first and then subsequent
>> perf_event_detach_bpf_prog needs bpf_event_mutex lock.
>> Such a senario caused a deadlock.
>>
>> As suggested by Danial, moving copy_to_user out of the
>
> Nit: typo :)
Oh, my bad. will correct.
>
>> bpf_event_mutex lock should fix the problem.
>>
>> Fixes: f371b304f12e ("bpf/tracing: allow user space to query prog array on the same tp")
>> Reported-by: syzbot+dc5ca0e4c9bfafaf2bae@...kaller.appspotmail.com
>> Signed-off-by: Yonghong Song <yhs@...com>
>> ---
>> include/linux/bpf.h | 4 ++--
>> kernel/bpf/core.c | 45 +++++++++++++++++++++++++++++----------------
>> kernel/trace/bpf_trace.c | 19 +++++++++++++++----
>> 3 files changed, 46 insertions(+), 22 deletions(-)
>>
>> Changelog:
>> v2 -> v3:
>> . Remove the redundant label in function perf_event_query_prog_array.
>> v1 -> v2:
>> . Use the common core function for prog_id copying for two
>> different prog_array copy routines, suggested by Alexei.
>>
> [...]
>> static void bpf_prog_free_deferred(struct work_struct *work)
>> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
>> index d88e96d..f505d43 100644
>> --- a/kernel/trace/bpf_trace.c
>> +++ b/kernel/trace/bpf_trace.c
>> @@ -977,6 +977,7 @@ int perf_event_query_prog_array(struct perf_event *event, void __user *info)
>> {
>> struct perf_event_query_bpf __user *uquery = info;
>> struct perf_event_query_bpf query = {};
>> + u32 *ids, prog_cnt, ids_len;
>> int ret;
>>
>> if (!capable(CAP_SYS_ADMIN))
>> @@ -985,16 +986,26 @@ int perf_event_query_prog_array(struct perf_event *event, void __user *info)
>> return -EINVAL;
>> if (copy_from_user(&query, uquery, sizeof(query)))
>> return -EFAULT;
>> - if (query.ids_len > BPF_TRACE_MAX_PROGS)
>> +
>> + ids_len = query.ids_len;
>> + if (ids_len > BPF_TRACE_MAX_PROGS)
>> return -E2BIG;
>> + ids = kcalloc(ids_len, sizeof(u32), GFP_USER | __GFP_NOWARN);
>> + if (!ids)
>> + return -ENOMEM;
>
> Fix looks good to me, but could you still add a comment stating that we don't
> need to check for ZERO_SIZE_PTR above since we handle this gracefully in the
> bpf_prog_array_copy_info() plus it's also required for the case where the user
> only wants to check for the uquery->prog_cnt, but nothing else.
Will add the comment and send another version.
Thanks.
>
>> mutex_lock(&bpf_event_mutex);
>> ret = bpf_prog_array_copy_info(event->tp_event->prog_array,
>> - uquery->ids,
>> - query.ids_len,
>> - &uquery->prog_cnt);
>> + ids,
>> + ids_len,
>> + &prog_cnt);
>> mutex_unlock(&bpf_event_mutex);
>>
>> + if (copy_to_user(&uquery->prog_cnt, &prog_cnt, sizeof(prog_cnt)) ||
>> + copy_to_user(uquery->ids, ids, ids_len * sizeof(u32)))
>> + ret = -EFAULT;
>> +
>> + kfree(ids);
>> return ret;
>> }
>
> Thanks,
> Daniel
>
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