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Date: Tue, 10 Apr 2018 10:54:50 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Yonghong Song <yhs@...com>, 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 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 :)
> 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.
> 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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