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[34.150.230.223]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-91e7dfdfb5fsm6279506d6.16.2026.11.03.18.10.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 Nov 2026 18:10:55 -0800 (PST) Date: Tue, 03 Nov 2026 21:10:54 -0500 From: Willem de Bruijn To: Eric Dumazet , netdev@vger.kernel.org, "David S. Miller" , Jakub Kicinski , Paolo Abeni Cc: Eric Dumazet , Simon Horman , Willem de Bruijn , "Michael S. Tsirkin" , =?UTF-8?B?RXVnZW5pbyBQw6lyZXo=?= , Hassan Sultan , virtualization@lists.linux.dev Message-ID: In-Reply-To: <20261103203113.550604-3-edumazet@kernel.org> References: <20261103203113.550604-1-edumazet@kernel.org> <20261103203113.550604-3-edumazet@kernel.org> Subject: Re: [PATCH net 2/3] selftests: net: tuntap: fix UDP checksum length in build_udp_packet_csum() X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Eric Dumazet wrote: > build_udp_packet_csum() passes udph->len, which is in network byte > order, as the number of bytes to checksum. On little-endian hosts this > reads up to 64KB past the UDP header and computes a wrong checksum. > > Existing callers did not crash only because they use packet buffers > of MAX_VNET_TUNNEL_PACKET_SZ bytes. > > Use ntohs(udph->len), as tap.c does in its own build_udp_packet(). > > Fixes: a942fcd72e97 ("selftest: tun: Introduce tuntap_helpers.h header for TUN/TAP testing") > Signed-off-by: Eric Dumazet Reviewed-by: Willem de Bruijn > --- > tools/testing/selftests/net/tuntap_helpers.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/tools/testing/selftests/net/tuntap_helpers.h b/tools/testing/selftests/net/tuntap_helpers.h > index d6c0437136ec..ac9b2da57a6d 100644 > --- a/tools/testing/selftests/net/tuntap_helpers.h > +++ b/tools/testing/selftests/net/tuntap_helpers.h > @@ -335,7 +335,7 @@ static inline void build_udp_packet_csum(uint8_t *buf, int family, > sum += htons(IPPROTO_UDP) + udph->len; > > if (!csum_off) > - sum += add_csum(buf, udph->len); > + sum += add_csum(buf, ntohs(udph->len)); > > udph->check = finish_ip_csum(sum); If respinning: we probably should also do CSUM_MANGLED_0 conversion here. And to zero udph->check first. All existing callers do. But the calloc in patch 3/3 does not. > } > -- > 2.53.0 >