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[27.51.89.168]) by smtp.gmail.com with ESMTPSA id 006d021491bc7-6a39a4a7797sm7988739eaf.6.2026.07.14.20.02.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Jul 2026 20:02:14 -0700 (PDT) Date: Wed, 15 Jul 2026 11:02:02 +0800 From: Shung-Hsi Yu To: Sun Jian Cc: bpf@vger.kernel.org, Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Eduard Zingerman , Emil Tsalapatis , Jiri Olsa , John Fastabend , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Shuah Khan , Song Liu , Yonghong Song , Matt Mullins , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH bpf v5 2/2] selftests/bpf: Cover negative buffer pointer offsets Message-ID: References: <20260714093846.18159-1-sun.jian.kdev@gmail.com> <20260714093846.18159-3-sun.jian.kdev@gmail.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260714093846.18159-3-sun.jian.kdev@gmail.com> On Tue, Jul 14, 2026 at 02:38:46AM -0700, Sun Jian wrote: > Add verifier coverage for constant negative offsets on PTR_TO_TP_BUFFER > and PTR_TO_BUF pointers. Both programs adjust the buffer pointer by -8 > and access it at offset zero, so the negative effective start must be > rejected at load time. > > Switch the raw tracepoint writable attach checks from nbd_send_request > to bpf_testmod_test_writable_bare_tp, avoiding a dependency on the NBD > tracepoint. Keep the existing past-end case and add a case with a > negative var_off compensated by a positive instruction offset. The > effective start remains non-negative, so the program loads, but its > access end exceeds the writable context size and > bpf_raw_tracepoint_open() must return -EINVAL. > > Reported-by: Shung-Hsi Yu > Link: https://lore.kernel.org/bpf/alRtilWhKw4zzMkI@u94a > Cc: stable@vger.kernel.org # 5.2.0 ... IMO it is slightly better to split this into two. First part would be [1] suggested by Eduard, and the second part would be the addition of negative offset test. That said, I checked that with v5.2 we do have PTR_TO_TP_BUFFER and PTR_TO_BUF support already (latter as PTR_TO_RDONLY_BUF and PTR_TO_RDWR_BUF), so there shouldn't be a problem having these tests back in stable. Acked-by: Shung-Hsi Yu 1: https://lore.kernel.org/bpf/3430dc0a2a141769a596ab21d7abdd86a0a804db.camel@gmail.com/2-tp-test.diff