netdev - Re: [PATCH bpf v4] bpf/tracing: fix a deadlock in perf_event_detach_bpf

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Message-ID: <7c19c01d-c636-b259-40db-b2cd0a79d628@iogearbox.net>
Date:   Wed, 11 Apr 2018 01:14:57 +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 v4] bpf/tracing: fix a deadlock in
 perf_event_detach_bpf_prog

On 04/10/2018 06:37 PM, 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:
> 
[...]
> 
> 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 Daniel, moving copy_to_user out of the
> 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>

Applied to bpf tree, thanks Yonghong!