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Message-ID: <87ec7f5c-83af-810d-f878-f214fa89c4cd@iogearbox.net>
Date: Thu, 16 Aug 2018 02:17:53 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Roman Gushchin <guro@...com>,
Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Yonghong Song <yhs@...com>, ast@...com, netdev@...r.kernel.org,
kernel-team@...com
Subject: Re: [PATCH bpf] bpf: fix a rcu usage warning in
bpf_prog_array_copy_core()
On 08/15/2018 02:08 AM, Roman Gushchin wrote:
> On Tue, Aug 14, 2018 at 04:59:45PM -0700, Alexei Starovoitov wrote:
>> On Tue, Aug 14, 2018 at 11:01:12AM -0700, Yonghong Song wrote:
>>> Commit 394e40a29788 ("bpf: extend bpf_prog_array to store pointers
>>> to the cgroup storage") refactored the bpf_prog_array_copy_core()
>>> to accommodate new structure bpf_prog_array_item which contains
>>> bpf_prog array itself.
>>>
>>> In the old code, we had
>>> perf_event_query_prog_array():
>>> mutex_lock(...)
>>> bpf_prog_array_copy_call():
>>> prog = rcu_dereference_check(array, 1)->progs
>>> bpf_prog_array_copy_core(prog, ...)
>>> mutex_unlock(...)
>>>
>>> With the above commit, we had
>>> perf_event_query_prog_array():
>>> mutex_lock(...)
>>> bpf_prog_array_copy_call():
>>> bpf_prog_array_copy_core(array, ...):
>>> item = rcu_dereference(array)->items;
>>> ...
>>> mutex_unlock(...)
>>>
>>> The new code will trigger a lockdep rcu checking warning.
>>> The fix is to change rcu_dereference() to rcu_dereference_check()
>>> to prevent such a warning.
>>>
>>> Reported-by: syzbot+6e72317008eef84a216b@...kaller.appspotmail.com
>>> Fixes: 394e40a29788 ("bpf: extend bpf_prog_array to store pointers to the cgroup storage")
>>> Cc: Roman Gushchin <guro@...com>
>>> Signed-off-by: Yonghong Song <yhs@...com>
Applied to bpf, thanks Yonghong!
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