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[2001:1c00:20d:1300:1b1c:4449:176a:89ea]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b9084e4c27bsm425855366b.39.2026.02.24.07.51.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Feb 2026 07:51:10 -0800 (PST) From: Eric Woudstra To: Michal Ostrowski , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: netdev@vger.kernel.org, Florian Westphal , Eric Woudstra , Nikolay Aleksandrov , Kees Cook Subject: [PATCH v20 net] net: pppoe: avoid zero-length arrays in struct pppoe_hdr Date: Tue, 24 Feb 2026 16:50:30 +0100 Message-ID: <20260224155030.106918-1-ericwouds@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Jakub Kicinski suggested following patch: W=1 C=1 GCC build gives us: net/bridge/netfilter/nf_conntrack_bridge.c: note: in included file (through ../include/linux/if_pppox.h, ../include/uapi/linux/netfilter_bridge.h, ../include/linux/netfilter_bridge.h): include/uapi/linux/if_pppox.h: 153:29: warning: array of flexible structures It doesn't like that hdr has a zero-length array which overlaps proto. The kernel code doesn't currently need those arrays. PPPoE connection is functional after applying this patch. Reviewed-by: Nikolay Aleksandrov Reviewed-by: Kees Cook Signed-off-by: Eric Woudstra --- This version was last send in: [PATCH v19 nf-next 1/5] net: pppoe: avoid zero-length arrays in struct pppoe_hdr Although it is needed to prevent warnings caused by my patches send to nf-next, it was asked to send this patch separately to netdev. drivers/net/ppp/pppoe.c | 2 +- include/uapi/linux/if_pppox.h | 4 ++++ 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/drivers/net/ppp/pppoe.c b/drivers/net/ppp/pppoe.c index 4275b393a454..7900cc3212a5 100644 --- a/drivers/net/ppp/pppoe.c +++ b/drivers/net/ppp/pppoe.c @@ -885,7 +885,7 @@ static int pppoe_sendmsg(struct socket *sock, struct msghdr *m, skb->protocol = cpu_to_be16(ETH_P_PPP_SES); ph = skb_put(skb, total_len + sizeof(struct pppoe_hdr)); - start = (char *)&ph->tag[0]; + start = (char *)ph + sizeof(*ph); error = memcpy_from_msg(start, m, total_len); if (error < 0) { diff --git a/include/uapi/linux/if_pppox.h b/include/uapi/linux/if_pppox.h index 9abd80dcc46f..29b804aa7474 100644 --- a/include/uapi/linux/if_pppox.h +++ b/include/uapi/linux/if_pppox.h @@ -122,7 +122,9 @@ struct sockaddr_pppol2tpv3in6 { struct pppoe_tag { __be16 tag_type; __be16 tag_len; +#ifndef __KERNEL__ char tag_data[]; +#endif } __attribute__ ((packed)); /* Tag identifiers */ @@ -150,7 +152,9 @@ struct pppoe_hdr { __u8 code; __be16 sid; __be16 length; +#ifndef __KERNEL__ struct pppoe_tag tag[]; +#endif } __packed; /* Length of entire PPPoE + PPP header */ -- 2.53.0