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[2a01:cb08:8949:7e00:cb3:32f6:3428:a027]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-458a7c91c0esm36554445e9.11.2025.08.01.02.47.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 01 Aug 2025 02:47:25 -0700 (PDT) Date: Fri, 1 Aug 2025 11:47:23 +0200 From: Paul Chaignon To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Martin KaFai Lau , netfilter-devel@vger.kernel.org, Pablo Neira Ayuso , Jozsef Kadlecsik , Petar Penkov , Florian Westphal Subject: [PATCH bpf 1/4] bpf: Check flow_dissector ctx accesses are aligned Message-ID: Precedence: bulk X-Mailing-List: netfilter-devel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline flow_dissector_is_valid_access doesn't check that the context access is aligned. As a consequence, an unaligned access within one of the exposed field is considered valid and later rejected by flow_dissector_convert_ctx_access when we try to convert it. The later rejection is problematic because it's reported as a verifier bug with a kernel warning and doesn't point to the right instruction in verifier logs. Fixes: d58e468b1112 ("flow_dissector: implements flow dissector BPF hook") Reported-by: syzbot+ccac90e482b2a81d74aa@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=ccac90e482b2a81d74aa Signed-off-by: Paul Chaignon --- net/core/filter.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/net/core/filter.c b/net/core/filter.c index c09a85c17496..da391e2b0788 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -9458,6 +9458,9 @@ static bool flow_dissector_is_valid_access(int off, int size, if (off < 0 || off >= sizeof(struct __sk_buff)) return false; + if (off % size != 0) + return false; + if (type == BPF_WRITE) return false; -- 2.43.0