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[2a01:cb08:8949:7e00:5b2c:732a:3e9f:a7f4]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b79c3ac093sm2623102f8f.9.2025.07.31.06.53.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 31 Jul 2025 06:53:44 -0700 (PDT) Date: Thu, 31 Jul 2025 15:53:43 +0200 From: Paul Chaignon To: syzbot Cc: andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org, daniel@iogearbox.net, eddyz87@gmail.com, haoluo@google.com, john.fastabend@gmail.com, jolsa@kernel.org, kpsingh@kernel.org, linux-kernel@vger.kernel.org, martin.lau@linux.dev, sdf@fomichev.me, song@kernel.org, syzkaller-bugs@googlegroups.com, yonghong.song@linux.dev Subject: Re: [syzbot] [bpf?] WARNING in convert_ctx_accesses Message-ID: References: <688ae0bf.050a0220.5d226.0011.GAE@google.com> <688b72e9.050a0220.5d226.0018.GAE@google.com> Precedence: bulk X-Mailing-List: linux-kernel@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: <688b72e9.050a0220.5d226.0018.GAE@google.com> This is happening because flow_dissector_is_valid_access matches on ranges (bpf_ctx_range) whereas flow_dissector_convert_ctx_access matches on offsets (offsetof). Hence an access to offsetof(struct __sk_buff, data_end) + 1 is considered valid and then fails during convertion. I'll send a fix asap. Paul On Thu, Jul 31, 2025 at 06:43:05AM -0700, syzbot wrote: > syzbot has bisected this issue to: > > commit 0df1a55afa832f463f9ad68ddc5de92230f1bc8a > Author: Paul Chaignon > Date: Tue Jul 1 18:36:15 2025 +0000 > > bpf: Warn on internal verifier errors > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=17d6aca2580000 > start commit: e8d780dcd957 Merge tag 'slab-for-6.17' of git://git.kernel.. > git tree: upstream > final oops: https://syzkaller.appspot.com/x/report.txt?x=1436aca2580000 > console output: https://syzkaller.appspot.com/x/log.txt?x=1036aca2580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=d32de89be62206c8 > dashboard link: https://syzkaller.appspot.com/bug?extid=ccac90e482b2a81d74aa > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=131049bc580000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11cc2cf0580000 > > Reported-by: syzbot+ccac90e482b2a81d74aa@syzkaller.appspotmail.com > Fixes: 0df1a55afa83 ("bpf: Warn on internal verifier errors") > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection