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net: pppoe: avoid zero-length arrays in struct pppoe_hdr 

Jakub Kicinski reported following issue in upcoming patches:

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

sparse 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 <razor@blackwall.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Eric Woudstra <ericwouds@gmail.com>
Link: https://patch.msgid.link/20260224155030.106918-1-ericwouds@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Woudstra 2026-02-24 16:50:30 +01:00 committed by Jakub Kicinski
parent 8debe7a223
commit 7717fbb140
2 changed files with 5 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/net/ppp/pppoe.c
View File

@ -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) {

4
include/uapi/linux/if_pppox.h
View File

@ -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 */