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AJvYcCXgobxnaT8HoBAZ0FQfANixI4F434UdLke1S2YgSGDQkM/sRsmNk+e8TpRRDzQUIG+P9NRnGJs=@vger.kernel.org X-Gm-Message-State: AOJu0YxvXSDXxAITXX8VQVf6IAX6ZzOKK9qW3d/qrfipkW+fkOvEPDkm ozzgMO8axoVmsDnk+Dj8v1m8b3aF6wyHvzZ4RBVGK05HvyFDDLLnIEfhTmDYNF/TNjqBQDJs8tp 5+HVWeZ7fD7eNa6fF0/GJL3wjTZJTEGo= X-Gm-Gg: ASbGncvDsj2hnKcNbOJ574vOpOVeNEGRVi+U4NeX1pZXiY+sBAWLE7uEzA5jN9DXA4m a9JcYAA3u/BoLSg+RkZtevGKCahhSnNGsCECXze55BHHxBYGxeGYyTyyF2mxM4SSQlfPc/EpSoT VMAUceGf0WaplAgGh6WzptW6Ld+fCl28nX8t+4hj97hUfgS2W+EYnCd4rO4xRX5gqqvOl+o+qLL 0NHLxpLVTgNIo4P+w== X-Google-Smtp-Source: AGHT+IFKP70JWp1/cr4TdNlPBWxCnWQMNyk7OxeuCiP2T5O/NjJy7Wk8Yux3WDbnvc/kyh4lFy8n9qpu4Xtn4gPKZsQ= X-Received: by 2002:a05:690c:64c8:b0:720:139d:4dcf with SMTP id 00721157ae682-720139d5b66mr97299627b3.12.1756215863019; Tue, 26 Aug 2025 06:44:23 -0700 (PDT) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20250825193918.3445531-1-ameryhung@gmail.com> <20250825193918.3445531-4-ameryhung@gmail.com> <20250825153923.0d98c69d@kernel.org> <20250826062019.2140dd84@kernel.org> In-Reply-To: <20250826062019.2140dd84@kernel.org> From: Amery Hung Date: Tue, 26 Aug 2025 06:44:12 -0700 X-Gm-Features: Ac12FXzHU8CEjaA58v6GMjiC8MirT5rJfphKvaQZCFg4OLrpH-rgKkR4FUpjtqU Message-ID: Subject: Re: [RFC bpf-next v1 3/7] bpf: Support pulling non-linear xdp data To: Jakub Kicinski Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, alexei.starovoitov@gmail.com, andrii@kernel.org, daniel@iogearbox.net, martin.lau@kernel.org, mohsin.bashr@gmail.com, saeedm@nvidia.com, tariqt@nvidia.com, mbloch@nvidia.com, maciej.fijalkowski@intel.com, kernel-team@meta.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, Aug 26, 2025 at 6:20=E2=80=AFAM Jakub Kicinski wr= ote: > > On Mon, 25 Aug 2025 22:12:21 -0700 Amery Hung wrote: > > > > + data_end =3D xdp->data + len; > > > > + delta =3D data_end - xdp->data_end; > > > > + > > > > + if (delta <=3D 0) > > > > + return 0; > > > > + > > > > + if (unlikely(data_end > data_hard_end)) > > > > + return -EINVAL; > > > > > > Is this safe against pointers wrapping on 32b systems? > > > > > > > You are right. This may be a problem. > > > > > Maybe it's better to do: > > > > > > if (unlikely(data_hard_end - xdp->data_end < delta)) > > > > > > ? > > > > But delta may be negative if the pointer wraps around and then the > > function will still continue. How about adding data_end < xdp->data > > check and reorganizing the checks like this? > > You already checked that delta is positive in the previous if (), > so I think it's safe. Admittedly having 3 separate conditions is > more readable but it's not strictly necessary. Up to you. Got it. I will change to the new set of checks. The original kfunc would return 0 when pointer wrapping happens and delta <=3D 0.