netdev - Re: [PATCH v2 bpf-next 12/17] bpf: Fix race in btf_resolve_helper

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <b51f14fc-8561-0a53-f5ef-f2497e2c66c2@fb.com>
Date:   Fri, 8 Nov 2019 05:31:23 +0000
From:   Alexei Starovoitov <ast@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Alexei Starovoitov <ast@...nel.org>
CC:     "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        "x86@...nel.org" <x86@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 12/17] bpf: Fix race in
 btf_resolve_helper_id()

On 11/7/19 9:13 PM, Andrii Nakryiko wrote:
> On Wed, Nov 6, 2019 at 9:48 PM Alexei Starovoitov <ast@...nel.org> wrote:
>>
>> btf_resolve_helper_id() caching logic is racy, since under root the verifier
>> can verify several programs in parallel. Fix it with extra spin_lock.
>>
>> Fixes: a7658e1a4164 ("bpf: Check types of arguments passed into helpers")
>> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
>> ---
>>   include/linux/bpf.h   |  3 ++-
>>   kernel/bpf/btf.c      | 34 +++++++++++++++++++++++++++++++++-
>>   kernel/bpf/verifier.c |  6 +-----
>>   3 files changed, 36 insertions(+), 7 deletions(-)
>>
> 
> [...]
> 
>> +       /* ok to race the search. The result is the same */
>> +       ret = __btf_resolve_helper_id(log, fn->func, arg);
>> +       if (!ret) {
>> +               bpf_log(log, "BTF resolution bug\n");
>> +               return -EFAULT;
>> +       }
>> +       spin_lock(&btf_resolve_lock);
>> +       if (*btf_id) {
>> +               ret = *btf_id;
>> +               goto out;
>> +       }
>> +       *btf_id = ret;
>> +out:
>> +       spin_unlock(&btf_resolve_lock);
> 
> Is this race a problem? Does it cause any issues? Given that even if
> you do parallel resolutions at the same time, they all will have to
> result in the same btf_id, so just setting it unconditionally multiple
> times without locking should be ok, no? Maybe WRITE_ONCE, but not sure
> why all the way to spinlock.

Hmm. Indeed. Let me switch to READ_ONCE/WRITE_ONCE.