On 10/25/25 08:23, Jakub Kicinski wrote:
On Fri, 24 Oct 2025 12:24:09 +0100 Gustavo A. R. Silva wrote:
On 10/24/25 01:25, Jakub Kicinski wrote:
On Tue, 21 Oct 2025 12:43:30 +0100 Gustavo A. R. Silva wrote:
struct ip_options_data {
- struct ip_options_rcu opt;
- char data[40];
+ TRAILING_OVERLAP(struct ip_options_rcu, opt, opt.__data,
+ char data[40];
+ );
};
Is there a way to reserve space for flexible length array on the stack
without resorting to any magic macros? This struct has total of 5 users.
Not that I know of. That's the reason why we had to implement macros like
TRAILING_OVERLAP(), DEFINE_FLEX(), DEFINE_RAW_FLEX().
Regarding these three macros, the simplest and least intrusive one to use is
actually TRAILING_OVERLAP(), when the flex-array member is not annotated with
the counted_by attribute (otherwise, DEFINE_FLEX() would be preferred).
Of course, the most straightforward alternative is to use fixed-size arrays
if flex arrays are not actually needed.
Honestly, I'm tired of the endless, nasty macros for no clear benefit.
This patch is not happening.
Not sure what you mean by "nasty" and "no clear benefit", but here is an
alternative. See it as RFC:
https://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux.git/commit/?h=testing/wfamnae-next20251117&id=e0547082214e61b1db0f5068da0daa3d11f992a5
[PATCH RFC][next] ipv4/inet_sock.h: Avoid thousands of
-Wflex-array-member-not-at-end warnings
Use DEFINE_RAW_FLEX() to avoid thousands of -Wflex-array-member-not-at-end
warnings.
Remove fixed-size array char data[40]; from struct ip_options_data, so
that flexible-array member struct ip_options_rcu::opt.__data[] ends last
in this (and other) structure(s).
Compensate for this by using the DEFINE_RAW_FLEX() helper to declare each
on-stack struct instance that contains struct ip_options_data as a member.
Signed-off-by: Gustavo A. R. Silva <[email protected]>
---
include/net/inet_sock.h | 1 -
net/ipv4/icmp.c | 88 +++++++++++++++++++++--------------------
net/ipv4/ip_output.c | 12 +++---
net/ipv4/ping.c | 6 +--
net/ipv4/raw.c | 6 +--
net/ipv4/udp.c | 6 +--
6 files changed, 60 insertions(+), 59 deletions(-)
diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index ac1c75975908..3b5da5e54673 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -63,7 +63,6 @@ struct ip_options_rcu {
struct ip_options_data {
struct ip_options_rcu opt;
- char data[40];
};
struct inet_request_sock {
diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 4abbec2f47ef..744d4e91cb9c 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -353,9 +353,11 @@ void icmp_out_count(struct net *net, unsigned char type)
static int icmp_glue_bits(void *from, char *to, int offset, int len, int odd,
struct sk_buff *skb)
{
- struct icmp_bxm *icmp_param = from;
+ DEFINE_RAW_FLEX(struct icmp_bxm, icmp_param, replyopts.opt.opt.__data,
40);
__wsum csum;
+ icmp_param = from;
+
csum = skb_copy_and_csum_bits(icmp_param->skb,
icmp_param->offset + offset,
to, len);
@@ -775,9 +777,9 @@ icmp_ext_append(struct net *net, struct sk_buff *skb_in,
struct icmphdr *icmph,
void __icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info,
const struct inet_skb_parm *parm)
{
+ DEFINE_RAW_FLEX(struct icmp_bxm, icmp_param, replyopts.opt.opt.__data,
40);
struct iphdr *iph;
int room;
- struct icmp_bxm icmp_param;
struct rtable *rt = skb_rtable(skb_in);
bool apply_ratelimit = false;
struct sk_buff *ext_skb;
@@ -906,7 +908,7 @@ void __icmp_send(struct sk_buff *skb_in, int type, int
code, __be32 info,
iph->tos;
mark = IP4_REPLY_MARK(net, skb_in->mark);
- if (__ip_options_echo(net, &icmp_param.replyopts.opt.opt, skb_in,
+ if (__ip_options_echo(net, &icmp_param->replyopts.opt.opt, skb_in,
&parm->opt))
goto out_unlock;
@@ -915,21 +917,21 @@ void __icmp_send(struct sk_buff *skb_in, int type, int
code, __be32 info,
* Prepare data for ICMP header.
*/
- icmp_param.data.icmph.type = type;
- icmp_param.data.icmph.code = code;
- icmp_param.data.icmph.un.gateway = info;
- icmp_param.data.icmph.checksum = 0;
- icmp_param.skb = skb_in;
- icmp_param.offset = skb_network_offset(skb_in);
+ icmp_param->data.icmph.type = type;
+ icmp_param->data.icmph.code = code;
+ icmp_param->data.icmph.un.gateway = info;
+ icmp_param->data.icmph.checksum = 0;
+ icmp_param->skb = skb_in;
+ icmp_param->offset = skb_network_offset(skb_in);
ipcm_init(&ipc);
ipc.tos = tos;
ipc.addr = iph->saddr;
- ipc.opt = &icmp_param.replyopts.opt;
+ ipc.opt = &icmp_param->replyopts.opt;
ipc.sockc.mark = mark;
rt = icmp_route_lookup(net, &fl4, skb_in, iph, saddr,
inet_dsfield_to_dscp(tos), mark, type, code,
- &icmp_param);
+ icmp_param);
if (IS_ERR(rt))
goto out_unlock;
@@ -942,7 +944,7 @@ void __icmp_send(struct sk_buff *skb_in, int type, int
code, __be32 info,
room = dst_mtu(&rt->dst);
if (room > 576)
room = 576;
- room -= sizeof(struct iphdr) + icmp_param.replyopts.opt.opt.optlen;
+ room -= sizeof(struct iphdr) + icmp_param->replyopts.opt.opt.optlen;
room -= sizeof(struct icmphdr);
/* Guard against tiny mtu. We need to include at least one
* IP network header for this message to make any sense.
@@ -950,15 +952,15 @@ void __icmp_send(struct sk_buff *skb_in, int type, int
code, __be32 info,
if (room <= (int)sizeof(struct iphdr))
goto ende;
- ext_skb = icmp_ext_append(net, skb_in, &icmp_param.data.icmph, room,
+ ext_skb = icmp_ext_append(net, skb_in, &icmp_param->data.icmph, room,
parm->iif);
if (ext_skb)
- icmp_param.skb = ext_skb;
+ icmp_param->skb = ext_skb;
- icmp_param.data_len = icmp_param.skb->len - icmp_param.offset;
- if (icmp_param.data_len > room)
- icmp_param.data_len = room;
- icmp_param.head_len = sizeof(struct icmphdr);
+ icmp_param->data_len = icmp_param->skb->len - icmp_param->offset;
+ if (icmp_param->data_len > room)
+ icmp_param->data_len = room;
+ icmp_param->head_len = sizeof(struct icmphdr);
/* if we don't have a source address at this point, fall back to the
* dummy address instead of sending out a packet with a source address
@@ -969,7 +971,7 @@ void __icmp_send(struct sk_buff *skb_in, int type, int
code, __be32 info,
trace_icmp_send(skb_in, type, code);
- icmp_push_reply(sk, &icmp_param, &fl4, &ipc, &rt);
+ icmp_push_reply(sk, icmp_param, &fl4, &ipc, &rt);
if (ext_skb)
consume_skb(ext_skb);
@@ -1206,7 +1208,7 @@ static enum skb_drop_reason icmp_redirect(struct sk_buff
*skb)
static enum skb_drop_reason icmp_echo(struct sk_buff *skb)
{
- struct icmp_bxm icmp_param;
+ DEFINE_RAW_FLEX(struct icmp_bxm, icmp_param, replyopts.opt.opt.__data,
40);
struct net *net;
net = skb_dst_dev_net_rcu(skb);
@@ -1214,18 +1216,18 @@ static enum skb_drop_reason icmp_echo(struct sk_buff
*skb)
if (READ_ONCE(net->ipv4.sysctl_icmp_echo_ignore_all))
return SKB_NOT_DROPPED_YET;
- icmp_param.data.icmph = *icmp_hdr(skb);
- icmp_param.skb = skb;
- icmp_param.offset = 0;
- icmp_param.data_len = skb->len;
- icmp_param.head_len = sizeof(struct icmphdr);
+ icmp_param->data.icmph = *icmp_hdr(skb);
+ icmp_param->skb = skb;
+ icmp_param->offset = 0;
+ icmp_param->data_len = skb->len;
+ icmp_param->head_len = sizeof(struct icmphdr);
- if (icmp_param.data.icmph.type == ICMP_ECHO)
- icmp_param.data.icmph.type = ICMP_ECHOREPLY;
- else if (!icmp_build_probe(skb, &icmp_param.data.icmph))
+ if (icmp_param->data.icmph.type == ICMP_ECHO)
+ icmp_param->data.icmph.type = ICMP_ECHOREPLY;
+ else if (!icmp_build_probe(skb, &icmp_param->data.icmph))
return SKB_NOT_DROPPED_YET;
- icmp_reply(&icmp_param, skb);
+ icmp_reply(icmp_param, skb);
return SKB_NOT_DROPPED_YET;
}
@@ -1353,7 +1355,7 @@ EXPORT_SYMBOL_GPL(icmp_build_probe);
*/
static enum skb_drop_reason icmp_timestamp(struct sk_buff *skb)
{
- struct icmp_bxm icmp_param;
+ DEFINE_RAW_FLEX(struct icmp_bxm, icmp_param, replyopts.opt.opt.__data,
40);
/*
* Too short.
*/
@@ -1363,19 +1365,19 @@ static enum skb_drop_reason icmp_timestamp(struct
sk_buff *skb)
/*
* Fill in the current time as ms since midnight UT:
*/
- icmp_param.data.times[1] = inet_current_timestamp();
- icmp_param.data.times[2] = icmp_param.data.times[1];
-
- BUG_ON(skb_copy_bits(skb, 0, &icmp_param.data.times[0], 4));
-
- icmp_param.data.icmph = *icmp_hdr(skb);
- icmp_param.data.icmph.type = ICMP_TIMESTAMPREPLY;
- icmp_param.data.icmph.code = 0;
- icmp_param.skb = skb;
- icmp_param.offset = 0;
- icmp_param.data_len = 0;
- icmp_param.head_len = sizeof(struct icmphdr) + 12;
- icmp_reply(&icmp_param, skb);
+ icmp_param->data.times[1] = inet_current_timestamp();
+ icmp_param->data.times[2] = icmp_param->data.times[1];
+
+ BUG_ON(skb_copy_bits(skb, 0, &icmp_param->data.times[0], 4));
+
+ icmp_param->data.icmph = *icmp_hdr(skb);
+ icmp_param->data.icmph.type = ICMP_TIMESTAMPREPLY;
+ icmp_param->data.icmph.code = 0;
+ icmp_param->skb = skb;
+ icmp_param->offset = 0;
+ icmp_param->data_len = 0;
+ icmp_param->head_len = sizeof(struct icmphdr) + 12;
+ icmp_reply(icmp_param, skb);
return SKB_NOT_DROPPED_YET;
out_err:
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index ff11d3a85a36..e0b20226b0b7 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1606,7 +1606,7 @@ void ip_send_unicast_reply(struct sock *sk, const struct
sock *orig_sk,
const struct ip_reply_arg *arg,
unsigned int len, u64 transmit_time, u32 txhash)
{
- struct ip_options_data replyopts;
+ DEFINE_RAW_FLEX(struct ip_options_data, replyopts, opt.opt.__data, 40);
struct ipcm_cookie ipc;
struct flowi4 fl4;
struct rtable *rt = skb_rtable(skb);
@@ -1615,18 +1615,18 @@ void ip_send_unicast_reply(struct sock *sk, const
struct sock *orig_sk,
int err;
int oif;
- if (__ip_options_echo(net, &replyopts.opt.opt, skb, sopt))
+ if (__ip_options_echo(net, &replyopts->opt.opt, skb, sopt))
return;
ipcm_init(&ipc);
ipc.addr = daddr;
ipc.sockc.transmit_time = transmit_time;
- if (replyopts.opt.opt.optlen) {
- ipc.opt = &replyopts.opt;
+ if (replyopts->opt.opt.optlen) {
+ ipc.opt = &replyopts->opt;
- if (replyopts.opt.opt.srr)
- daddr = replyopts.opt.opt.faddr;
+ if (replyopts->opt.opt.srr)
+ daddr = replyopts->opt.opt.faddr;
}
oif = arg->bound_dev_if;
diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
index ad56588107cc..ebc7d24a4a68 100644
--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -690,6 +690,7 @@ EXPORT_IPV6_MOD_GPL(ping_common_sendmsg);
static int ping_v4_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
{
+ DEFINE_RAW_FLEX(struct ip_options_data, opt_copy, opt.opt.__data, 40);
struct net *net = sock_net(sk);
struct flowi4 fl4;
struct inet_sock *inet = inet_sk(sk);
@@ -697,7 +698,6 @@ static int ping_v4_sendmsg(struct sock *sk, struct msghdr
*msg, size_t len)
struct icmphdr user_icmph;
struct pingfakehdr pfh;
struct rtable *rt = NULL;
- struct ip_options_data opt_copy;
int free = 0;
__be32 saddr, daddr, faddr;
u8 scope;
@@ -746,9 +746,9 @@ static int ping_v4_sendmsg(struct sock *sk, struct msghdr
*msg, size_t len)
rcu_read_lock();
inet_opt = rcu_dereference(inet->inet_opt);
if (inet_opt) {
- memcpy(&opt_copy, inet_opt,
+ memcpy(opt_copy, inet_opt,
sizeof(*inet_opt) + inet_opt->opt.optlen);
- ipc.opt = &opt_copy.opt;
+ ipc.opt = &opt_copy->opt;
}
rcu_read_unlock();
}
diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index 5998c4cc6f47..802ebde0246d 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -481,6 +481,7 @@ static int raw_getfrag(void *from, char *to, int offset,
int len, int odd,
static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
{
+ DEFINE_RAW_FLEX(struct ip_options_data, opt_copy, opt.opt.__data, 40);
struct inet_sock *inet = inet_sk(sk);
struct net *net = sock_net(sk);
struct ipcm_cookie ipc;
@@ -491,7 +492,6 @@ static int raw_sendmsg(struct sock *sk, struct msghdr *msg,
size_t len)
__be32 daddr;
__be32 saddr;
int uc_index, err;
- struct ip_options_data opt_copy;
struct raw_frag_vec rfv;
int hdrincl;
@@ -561,9 +561,9 @@ static int raw_sendmsg(struct sock *sk, struct msghdr *msg,
size_t len)
rcu_read_lock();
inet_opt = rcu_dereference(inet->inet_opt);
if (inet_opt) {
- memcpy(&opt_copy, inet_opt,
+ memcpy(opt_copy, inet_opt,
sizeof(*inet_opt) + inet_opt->opt.optlen);
- ipc.opt = &opt_copy.opt;
+ ipc.opt = &opt_copy->opt;
}
rcu_read_unlock();
}
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index ffe074cb5865..fa2c4eeed55c 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1269,6 +1269,7 @@ EXPORT_IPV6_MOD_GPL(udp_cmsg_send);
int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
{
+ DEFINE_RAW_FLEX(struct ip_options_data, opt_copy, opt.opt.__data, 40);
struct inet_sock *inet = inet_sk(sk);
struct udp_sock *up = udp_sk(sk);
DECLARE_SOCKADDR(struct sockaddr_in *, usin, msg->msg_name);
@@ -1286,7 +1287,6 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg,
size_t len)
int corkreq = udp_test_bit(CORK, sk) || msg->msg_flags & MSG_MORE;
int (*getfrag)(void *, char *, int, int, int, struct sk_buff *);
struct sk_buff *skb;
- struct ip_options_data opt_copy;
int uc_index;
if (len > 0xFFFF)
@@ -1368,9 +1368,9 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg,
size_t len)
rcu_read_lock();
inet_opt = rcu_dereference(inet->inet_opt);
if (inet_opt) {
- memcpy(&opt_copy, inet_opt,
+ memcpy(opt_copy, inet_opt,
sizeof(*inet_opt) + inet_opt->opt.optlen);
- ipc.opt = &opt_copy.opt;
+ ipc.opt = &opt_copy->opt;
}
rcu_read_unlock();
}
--
2.43.0
Thanks
-Gustavo
