[PATCH 2/3] net: Remove accidental VLAs from proc buffers

[Kees Cook <keescook@chromium.org>]

In the quest to remove all stack VLAs from the kernel[1], this refactors
the stack array size calculation to avoid using max(), which makes the
compiler think the size isn't fixed.

[1] https://lkml.org/lkml/2018/3/7/621

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 net/ipv4/proc.c | 10 ++++------
 net/ipv6/proc.c | 10 ++++------
 2 files changed, 8 insertions(+), 12 deletions(-)

diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index dc5edc8f7564..c23c43803435 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -46,8 +46,6 @@
 #include <net/sock.h>
 #include <net/raw.h>
 
-#define TCPUDP_MIB_MAX max_t(u32, UDP_MIB_MAX, TCP_MIB_MAX)
-
 /*
  *	Report socket allocation statistics [mea@utu.fi]
  */
@@ -400,11 +398,11 @@ static int snmp_seq_show_ipstats(struct seq_file *seq, void *v)
 
 static int snmp_seq_show_tcp_udp(struct seq_file *seq, void *v)
 {
-	unsigned long buff[TCPUDP_MIB_MAX];
+	unsigned long buff[SIMPLE_MAX(UDP_MIB_MAX, TCP_MIB_MAX)];
 	struct net *net = seq->private;
 	int i;
 
-	memset(buff, 0, TCPUDP_MIB_MAX * sizeof(unsigned long));
+	memset(buff, 0, sizeof(buff));
 
 	seq_puts(seq, "\nTcp:");
 	for (i = 0; snmp4_tcp_list[i].name; i++)
@@ -421,7 +419,7 @@ static int snmp_seq_show_tcp_udp(struct seq_file *seq, void *v)
 			seq_printf(seq, " %lu", buff[i]);
 	}
 
-	memset(buff, 0, TCPUDP_MIB_MAX * sizeof(unsigned long));
+	memset(buff, 0, sizeof(buff));
 
 	snmp_get_cpu_field_batch(buff, snmp4_udp_list,
 				 net->mib.udp_statistics);
@@ -432,7 +430,7 @@ static int snmp_seq_show_tcp_udp(struct seq_file *seq, void *v)
 	for (i = 0; snmp4_udp_list[i].name; i++)
 		seq_printf(seq, " %lu", buff[i]);
 
-	memset(buff, 0, TCPUDP_MIB_MAX * sizeof(unsigned long));
+	memset(buff, 0, sizeof(buff));
 
 	/* the UDP and UDP-Lite MIBs are the same */
 	seq_puts(seq, "\nUdpLite:");
diff --git a/net/ipv6/proc.c b/net/ipv6/proc.c
index b67814242f78..5b0874c26802 100644
--- a/net/ipv6/proc.c
+++ b/net/ipv6/proc.c
@@ -30,10 +30,8 @@
 #include <net/transp_v6.h>
 #include <net/ipv6.h>
 
-#define MAX4(a, b, c, d) \
-	max_t(u32, max_t(u32, a, b), max_t(u32, c, d))
-#define SNMP_MIB_MAX MAX4(UDP_MIB_MAX, TCP_MIB_MAX, \
-			IPSTATS_MIB_MAX, ICMP_MIB_MAX)
+#define SNMP_MIB_MAX SIMPLE_MAX(SIMPLE_MAX(UDP_MIB_MAX, TCP_MIB_MAX), \
+				SIMPLE_MAX(IPSTATS_MIB_MAX, ICMP_MIB_MAX))
 
 static int sockstat6_seq_show(struct seq_file *seq, void *v)
 {
@@ -199,7 +197,7 @@ static void snmp6_seq_show_item(struct seq_file *seq, void __percpu *pcpumib,
 	int i;
 
 	if (pcpumib) {
-		memset(buff, 0, sizeof(unsigned long) * SNMP_MIB_MAX);
+		memset(buff, 0, sizeof(buff));
 
 		snmp_get_cpu_field_batch(buff, itemlist, pcpumib);
 		for (i = 0; itemlist[i].name; i++)
@@ -218,7 +216,7 @@ static void snmp6_seq_show_item64(struct seq_file *seq, void __percpu *mib,
 	u64 buff64[SNMP_MIB_MAX];
 	int i;
 
-	memset(buff64, 0, sizeof(u64) * SNMP_MIB_MAX);
+	memset(buff64, 0, sizeof(buff64));
 
 	snmp_get_cpu_field64_batch(buff64, itemlist, mib, syncpoff);
 	for (i = 0; itemlist[i].name; i++)
-- 
2.7.4