From mboxrd@z Thu Jan 1 00:00:00 1970 From: Song Liu Subject: Re: [PATCH bpf-next 1/6] bpf: btf: Avoid WARN_ON when CONFIG_REFCOUNT_FULL=y Date: Tue, 8 May 2018 21:09:05 +0000 Message-ID: <66DB0A5D-04A4-4F6A-AF44-166D2FE9ACF6@fb.com> References: <20180504214955.1058805-1-kafai@fb.com> <20180504214955.1058805-2-kafai@fb.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Cc: Networking , Alexei Starovoitov , Daniel Borkmann , Kernel Team To: Martin Lau Return-path: Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:56232 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751533AbeEHVKi (ORCPT ); Tue, 8 May 2018 17:10:38 -0400 In-Reply-To: <20180504214955.1058805-2-kafai@fb.com> Content-Language: en-US Content-ID: Sender: netdev-owner@vger.kernel.org List-ID: > On May 4, 2018, at 2:49 PM, Martin KaFai Lau wrote: >=20 > If CONFIG_REFCOUNT_FULL=3Dy, refcount_inc() WARN when refcount is 0. > When creating a new btf, the initial btf->refcnt is 0 and > triggered the following: >=20 > [ 34.855452] refcount_t: increment on 0; use-after-free. > [ 34.856252] WARNING: CPU: 6 PID: 1857 at lib/refcount.c:153 refcount_i= nc+0x26/0x30 > .... > [ 34.868809] Call Trace: > [ 34.869168] btf_new_fd+0x1af6/0x24d0 > [ 34.869645] ? btf_type_seq_show+0x200/0x200 > [ 34.870212] ? lock_acquire+0x3b0/0x3b0 > [ 34.870726] ? security_capable+0x54/0x90 > [ 34.871247] __x64_sys_bpf+0x1b2/0x310 > [ 34.871761] ? __ia32_sys_bpf+0x310/0x310 > [ 34.872285] ? bad_area_access_error+0x310/0x310 > [ 34.872894] do_syscall_64+0x95/0x3f0 >=20 > This patch uses refcount_set() instead. >=20 > Reported-by: Yonghong Song > Tested-by: Yonghong Song > Signed-off-by: Martin KaFai Lau > --- > kernel/bpf/btf.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) >=20 > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c > index 22e1046a1a86..fa0dce0452e7 100644 > --- a/kernel/bpf/btf.c > +++ b/kernel/bpf/btf.c > @@ -1977,7 +1977,7 @@ static struct btf *btf_parse(void __user *btf_data,= u32 btf_data_size, >=20 > if (!err) { > btf_verifier_env_free(env); > - btf_get(btf); > + refcount_set(&btf->refcnt, 1); > return btf; > } >=20 > --=20 > 2.9.5 >=20 Acked-by: Song Liu =