Re: [PATCHv2 net-next] ipvs: reduce stack usage for sockopt data

[Pablo Neira Ayuso <pablo@netfilter.org>]

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Hi Julian,

On Wed, Sep 03, 2014 at 12:02:49AM +0300, Julian Anastasov wrote:
> Use union to reserve the required stack space for sockopt data
> which is less than the currently hardcoded value of 128.
> Now the tables for commands should be more readable.
> The checks added for readability are optimized by compiler,
> others warn at compile time if command uses too much
> stack or exceeds the storage of set_arglen and get_arglen.
> 
> As Dan Carpenter points out, we can run for unprivileged user,
> so we can silent some error messages.
> 
> Signed-off-by: Julian Anastasov <ja@ssi.bg>
> CC: Dan Carpenter <dan.carpenter@oracle.com>
> CC: Andrey Utkin <andrey.krieger.utkin@gmail.com>
> CC: David Binderman <dcb314@hotmail.com>
> ---
> 
> This is 2nd version. I removed the macros and tried to
> fit in 80 columns... Pablo, please check this version.
> Also, let us know if you are going to apply the final
> version directly or whether Simon should take it first.
> Thanks!

Thanks for spinning a second version. I took it over and made some
minor comestic changes. I noticed SET_CMDID() is equivalent to
GET_CMDID() so, while at it, I have merged them. This allowed me to
fit the structure in 80-chars per column by using spaces to pad the
initialization area (I remeber to have seen this trick in other parts
of the kernel code).

An another question, in do_ip_vs_get_ctl() I can see:

+       copylen = get_arglen[CMDID(cmd)];
+       if (*len < (int) copylen || *len < 0) {

len is signed, the casting also enforces signed arithmetics. copylen
can be 0 at worst case for unused options. Perhaps I'm overlooking
something but I think *len < 0 is redundant.

Let me know, I can mangle that here. Thanks!

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From 1b07935c334cdf05d9762306342548cb8673ca2c Mon Sep 17 00:00:00 2001
From: Julian Anastasov <ja@ssi.bg>
Date: Wed, 3 Sep 2014 00:02:49 +0300
Subject: [PATCH] ipvs: reduce stack usage for sockopt data

Use union to reserve the required stack space for sockopt data
which is less than the currently hardcoded value of 128.
Now the tables for commands should be more readable.
The checks added for readability are optimized by compiler,
others warn at compile time if command uses too much
stack or exceeds the storage of set_arglen and get_arglen.

As Dan Carpenter points out, we can run for unprivileged user,
so we can silent some error messages.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
CC: Dan Carpenter <dan.carpenter@oracle.com>
CC: Andrey Utkin <andrey.krieger.utkin@gmail.com>
CC: David Binderman <dcb314@hotmail.com>
---
 net/netfilter/ipvs/ip_vs_ctl.c |  112 ++++++++++++++++++++++------------------
 1 file changed, 62 insertions(+), 50 deletions(-)

diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
index fd3f444..fd103b1 100644
--- a/net/netfilter/ipvs/ip_vs_ctl.c
+++ b/net/netfilter/ipvs/ip_vs_ctl.c
@@ -2180,28 +2180,41 @@ static int ip_vs_set_timeout(struct net *net, struct ip_vs_timeout_user *u)
 }
 
 
-#define SET_CMDID(cmd)		(cmd - IP_VS_BASE_CTL)
-#define SERVICE_ARG_LEN		(sizeof(struct ip_vs_service_user))
-#define SVCDEST_ARG_LEN		(sizeof(struct ip_vs_service_user) +	\
-				 sizeof(struct ip_vs_dest_user))
-#define TIMEOUT_ARG_LEN		(sizeof(struct ip_vs_timeout_user))
-#define DAEMON_ARG_LEN		(sizeof(struct ip_vs_daemon_user))
-#define MAX_ARG_LEN		SVCDEST_ARG_LEN
-
-static const unsigned char set_arglen[SET_CMDID(IP_VS_SO_SET_MAX)+1] = {
-	[SET_CMDID(IP_VS_SO_SET_ADD)]		= SERVICE_ARG_LEN,
-	[SET_CMDID(IP_VS_SO_SET_EDIT)]		= SERVICE_ARG_LEN,
-	[SET_CMDID(IP_VS_SO_SET_DEL)]		= SERVICE_ARG_LEN,
-	[SET_CMDID(IP_VS_SO_SET_FLUSH)]		= 0,
-	[SET_CMDID(IP_VS_SO_SET_ADDDEST)]	= SVCDEST_ARG_LEN,
-	[SET_CMDID(IP_VS_SO_SET_DELDEST)]	= SVCDEST_ARG_LEN,
-	[SET_CMDID(IP_VS_SO_SET_EDITDEST)]	= SVCDEST_ARG_LEN,
-	[SET_CMDID(IP_VS_SO_SET_TIMEOUT)]	= TIMEOUT_ARG_LEN,
-	[SET_CMDID(IP_VS_SO_SET_STARTDAEMON)]	= DAEMON_ARG_LEN,
-	[SET_CMDID(IP_VS_SO_SET_STOPDAEMON)]	= DAEMON_ARG_LEN,
-	[SET_CMDID(IP_VS_SO_SET_ZERO)]		= SERVICE_ARG_LEN,
+#define CMDID(cmd)		(cmd - IP_VS_BASE_CTL)
+
+struct ip_vs_svcdest_user {
+	struct ip_vs_service_user	s;
+	struct ip_vs_dest_user		d;
+};
+
+static const unsigned char set_arglen[CMDID(IP_VS_SO_SET_MAX) + 1] = {
+	[CMDID(IP_VS_SO_SET_ADD)]         = sizeof(struct ip_vs_service_user),
+	[CMDID(IP_VS_SO_SET_EDIT)]        = sizeof(struct ip_vs_service_user),
+	[CMDID(IP_VS_SO_SET_DEL)]         = sizeof(struct ip_vs_service_user),
+	[CMDID(IP_VS_SO_SET_ADDDEST)]     = sizeof(struct ip_vs_svcdest_user),
+	[CMDID(IP_VS_SO_SET_DELDEST)]     = sizeof(struct ip_vs_svcdest_user),
+	[CMDID(IP_VS_SO_SET_EDITDEST)]    = sizeof(struct ip_vs_svcdest_user),
+	[CMDID(IP_VS_SO_SET_TIMEOUT)]     = sizeof(struct ip_vs_timeout_user),
+	[CMDID(IP_VS_SO_SET_STARTDAEMON)] = sizeof(struct ip_vs_daemon_user),
+	[CMDID(IP_VS_SO_SET_STOPDAEMON)]  = sizeof(struct ip_vs_daemon_user),
+	[CMDID(IP_VS_SO_SET_ZERO)]        = sizeof(struct ip_vs_service_user),
 };
 
+union ip_vs_set_arglen {
+	struct ip_vs_service_user	field_IP_VS_SO_SET_ADD;
+	struct ip_vs_service_user	field_IP_VS_SO_SET_EDIT;
+	struct ip_vs_service_user	field_IP_VS_SO_SET_DEL;
+	struct ip_vs_svcdest_user	field_IP_VS_SO_SET_ADDDEST;
+	struct ip_vs_svcdest_user	field_IP_VS_SO_SET_DELDEST;
+	struct ip_vs_svcdest_user	field_IP_VS_SO_SET_EDITDEST;
+	struct ip_vs_timeout_user	field_IP_VS_SO_SET_TIMEOUT;
+	struct ip_vs_daemon_user	field_IP_VS_SO_SET_STARTDAEMON;
+	struct ip_vs_daemon_user	field_IP_VS_SO_SET_STOPDAEMON;
+	struct ip_vs_service_user	field_IP_VS_SO_SET_ZERO;
+};
+
+#define MAX_SET_ARGLEN	sizeof(union ip_vs_set_arglen)
+
 static void ip_vs_copy_usvc_compat(struct ip_vs_service_user_kern *usvc,
 				  struct ip_vs_service_user *usvc_compat)
 {
@@ -2239,7 +2252,7 @@ do_ip_vs_set_ctl(struct sock *sk, int cmd, void __user *user, unsigned int len)
 {
 	struct net *net = sock_net(sk);
 	int ret;
-	unsigned char arg[MAX_ARG_LEN];
+	unsigned char arg[MAX_SET_ARGLEN];
 	struct ip_vs_service_user *usvc_compat;
 	struct ip_vs_service_user_kern usvc;
 	struct ip_vs_service *svc;
@@ -2247,16 +2260,15 @@ do_ip_vs_set_ctl(struct sock *sk, int cmd, void __user *user, unsigned int len)
 	struct ip_vs_dest_user_kern udest;
 	struct netns_ipvs *ipvs = net_ipvs(net);
 
+	BUILD_BUG_ON(sizeof(arg) > 255);
 	if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))
 		return -EPERM;
 
 	if (cmd < IP_VS_BASE_CTL || cmd > IP_VS_SO_SET_MAX)
 		return -EINVAL;
-	if (len < 0 || len >  MAX_ARG_LEN)
-		return -EINVAL;
-	if (len != set_arglen[SET_CMDID(cmd)]) {
-		pr_err("set_ctl: len %u != %u\n",
-		       len, set_arglen[SET_CMDID(cmd)]);
+	if (len != set_arglen[CMDID(cmd)]) {
+		IP_VS_DBG(1, "set_ctl: len %u != %u\n",
+			  len, set_arglen[CMDID(cmd)]);
 		return -EINVAL;
 	}
 
@@ -2512,51 +2524,51 @@ __ip_vs_get_timeouts(struct net *net, struct ip_vs_timeout_user *u)
 #endif
 }
 
+static const unsigned char get_arglen[CMDID(IP_VS_SO_GET_MAX) + 1] = {
+	[CMDID(IP_VS_SO_GET_VERSION)]  = 64,
+	[CMDID(IP_VS_SO_GET_INFO)]     = sizeof(struct ip_vs_getinfo),
+	[CMDID(IP_VS_SO_GET_SERVICES)] = sizeof(struct ip_vs_get_services),
+	[CMDID(IP_VS_SO_GET_SERVICE)]  = sizeof(struct ip_vs_service_entry),
+	[CMDID(IP_VS_SO_GET_DESTS)]    = sizeof(struct ip_vs_get_dests),
+	[CMDID(IP_VS_SO_GET_TIMEOUT)]  = sizeof(struct ip_vs_timeout_user),
+	[CMDID(IP_VS_SO_GET_DAEMON)]   = 2 * sizeof(struct ip_vs_daemon_user),
+};
 
-#define GET_CMDID(cmd)		(cmd - IP_VS_BASE_CTL)
-#define GET_INFO_ARG_LEN	(sizeof(struct ip_vs_getinfo))
-#define GET_SERVICES_ARG_LEN	(sizeof(struct ip_vs_get_services))
-#define GET_SERVICE_ARG_LEN	(sizeof(struct ip_vs_service_entry))
-#define GET_DESTS_ARG_LEN	(sizeof(struct ip_vs_get_dests))
-#define GET_TIMEOUT_ARG_LEN	(sizeof(struct ip_vs_timeout_user))
-#define GET_DAEMON_ARG_LEN	(sizeof(struct ip_vs_daemon_user) * 2)
-
-static const unsigned char get_arglen[GET_CMDID(IP_VS_SO_GET_MAX)+1] = {
-	[GET_CMDID(IP_VS_SO_GET_VERSION)]	= 64,
-	[GET_CMDID(IP_VS_SO_GET_INFO)]		= GET_INFO_ARG_LEN,
-	[GET_CMDID(IP_VS_SO_GET_SERVICES)]	= GET_SERVICES_ARG_LEN,
-	[GET_CMDID(IP_VS_SO_GET_SERVICE)]	= GET_SERVICE_ARG_LEN,
-	[GET_CMDID(IP_VS_SO_GET_DESTS)]		= GET_DESTS_ARG_LEN,
-	[GET_CMDID(IP_VS_SO_GET_TIMEOUT)]	= GET_TIMEOUT_ARG_LEN,
-	[GET_CMDID(IP_VS_SO_GET_DAEMON)]	= GET_DAEMON_ARG_LEN,
+union ip_vs_get_arglen {
+	char				field_IP_VS_SO_GET_VERSION[64];
+	struct ip_vs_getinfo		field_IP_VS_SO_GET_INFO;
+	struct ip_vs_get_services	field_IP_VS_SO_GET_SERVICES;
+	struct ip_vs_service_entry	field_IP_VS_SO_GET_SERVICE;
+	struct ip_vs_get_dests		field_IP_VS_SO_GET_DESTS;
+	struct ip_vs_timeout_user	field_IP_VS_SO_GET_TIMEOUT;
+	struct ip_vs_daemon_user	field_IP_VS_SO_GET_DAEMON[2];
 };
 
+#define MAX_GET_ARGLEN	sizeof(union ip_vs_get_arglen)
+
 static int
 do_ip_vs_get_ctl(struct sock *sk, int cmd, void __user *user, int *len)
 {
-	unsigned char arg[128];
+	unsigned char arg[MAX_GET_ARGLEN];
 	int ret = 0;
 	unsigned int copylen;
 	struct net *net = sock_net(sk);
 	struct netns_ipvs *ipvs = net_ipvs(net);
 
 	BUG_ON(!net);
+	BUILD_BUG_ON(sizeof(arg) > 255);
 	if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))
 		return -EPERM;
 
 	if (cmd < IP_VS_BASE_CTL || cmd > IP_VS_SO_GET_MAX)
 		return -EINVAL;
 
-	if (*len < get_arglen[GET_CMDID(cmd)]) {
-		pr_err("get_ctl: len %u < %u\n",
-		       *len, get_arglen[GET_CMDID(cmd)]);
+	copylen = get_arglen[CMDID(cmd)];
+	if (*len < (int) copylen || *len < 0) {
+		IP_VS_DBG(1, "get_ctl: len %d < %u\n", *len, copylen);
 		return -EINVAL;
 	}
 
-	copylen = get_arglen[GET_CMDID(cmd)];
-	if (copylen > 128)
-		return -EINVAL;