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[85.204.121.218]) by smtp.gmail.com with ESMTPSA id f5sm2062432lfh.52.2019.10.18.02.15.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Oct 2019 02:15:40 -0700 (PDT) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id 8398C1804C9; Fri, 18 Oct 2019 11:15:39 +0200 (CEST) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Jakub Kicinski Cc: daniel@iogearbox.net, ast@fb.com, bpf@vger.kernel.org, netdev@vger.kernel.org, Tetsuo Handa Subject: Re: [PATCH bpf] xdp: Prevent overflow in devmap_hash cost calculation for 32-bit builds In-Reply-To: <20191017115236.17895561@cakuba.netronome.com> References: <20191017105702.2807093-1-toke@redhat.com> <20191017115236.17895561@cakuba.netronome.com> X-Clacks-Overhead: GNU Terry Pratchett Date: Fri, 18 Oct 2019 11:15:39 +0200 Message-ID: <87y2xie7no.fsf@toke.dk> MIME-Version: 1.0 X-MC-Unique: I8buHJo5PPecfmYiTAYeCQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Jakub Kicinski writes: > On Thu, 17 Oct 2019 12:57:02 +0200, Toke H=C3=B8iland-J=C3=B8rgensen wrot= e: >> Tetsuo pointed out that without an explicit cast, the cost calculation f= or >> devmap_hash type maps could overflow on 32-bit builds. This adds the >> missing cast. >>=20 >> Fixes: 6f9d451ab1a3 ("xdp: Add devmap_hash map type for looking up devic= es by hashed index") >> Reported-by: Tetsuo Handa >> Signed-off-by: Toke H=C3=B8iland-J=C3=B8rgensen >> --- >> kernel/bpf/devmap.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >>=20 >> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c >> index a0a1153da5ae..e34fac6022eb 100644 >> --- a/kernel/bpf/devmap.c >> +++ b/kernel/bpf/devmap.c >> @@ -128,7 +128,7 @@ static int dev_map_init_map(struct bpf_dtab *dtab, u= nion bpf_attr *attr) >> =20 >> =09=09if (!dtab->n_buckets) /* Overflow check */ >> =09=09=09return -EINVAL; >> -=09=09cost +=3D sizeof(struct hlist_head) * dtab->n_buckets; >> +=09=09cost +=3D (u64) sizeof(struct hlist_head) * dtab->n_buckets; > > array_size()? Well, array_size does this: =09if (check_mul_overflow(a, b, &bytes)) =09=09return SIZE_MAX; However, we don't to return SIZE_MAX on overflow, we want the calculation itself to be done in 64 bits so it won't overflow... Or? -Toke