[PATCH v4 2/2] Remove false-positive VLAs when using max()

[Kees Cook <keescook@chromium.org>]

As part of removing VLAs from the kernel[1], we want to build with -Wvla,
but it is overly pessimistic and only accepts constant expressions for
stack array sizes, instead of also constant values. The max() macro
triggers the warning, so this refactors these uses of max() to use the
new const_max() instead.

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

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/input/touchscreen/cyttsp4_core.c |  2 +-
 fs/btrfs/tree-checker.c                  |  3 ++-
 lib/vsprintf.c                           |  4 ++--
 net/ipv4/proc.c                          |  8 ++++----
 net/ipv6/proc.c                          | 10 ++++------
 5 files changed, 13 insertions(+), 14 deletions(-)

diff --git a/drivers/input/touchscreen/cyttsp4_core.c b/drivers/input/touchscreen/cyttsp4_core.c
index 727c3232517c..f89497940051 100644
--- a/drivers/input/touchscreen/cyttsp4_core.c
+++ b/drivers/input/touchscreen/cyttsp4_core.c
@@ -868,7 +868,7 @@ static void cyttsp4_get_mt_touches(struct cyttsp4_mt_data *md, int num_cur_tch)
 	struct cyttsp4_touch tch;
 	int sig;
 	int i, j, t = 0;
-	int ids[max(CY_TMA1036_MAX_TCH, CY_TMA4XX_MAX_TCH)];
+	int ids[const_max(CY_TMA1036_MAX_TCH, CY_TMA4XX_MAX_TCH)];
 
 	memset(ids, 0, si->si_ofs.tch_abs[CY_TCH_T].max * sizeof(int));
 	for (i = 0; i < num_cur_tch; i++) {
diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
index c3c8d48f6618..1ddd6cc3c4fc 100644
--- a/fs/btrfs/tree-checker.c
+++ b/fs/btrfs/tree-checker.c
@@ -341,7 +341,8 @@ static int check_dir_item(struct btrfs_root *root,
 		 */
 		if (key->type == BTRFS_DIR_ITEM_KEY ||
 		    key->type == BTRFS_XATTR_ITEM_KEY) {
-			char namebuf[max(BTRFS_NAME_LEN, XATTR_NAME_MAX)];
+			char namebuf[const_max(BTRFS_NAME_LEN,
+					       XATTR_NAME_MAX)];
 
 			read_extent_buffer(leaf, namebuf,
 					(unsigned long)(di + 1), name_len);
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index d7a708f82559..9d5610b643ce 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -744,8 +744,8 @@ char *resource_string(char *buf, char *end, struct resource *res,
 #define FLAG_BUF_SIZE		(2 * sizeof(res->flags))
 #define DECODED_BUF_SIZE	sizeof("[mem - 64bit pref window disabled]")
 #define RAW_BUF_SIZE		sizeof("[mem - flags 0x]")
-	char sym[max(2*RSRC_BUF_SIZE + DECODED_BUF_SIZE,
-		     2*RSRC_BUF_SIZE + FLAG_BUF_SIZE + RAW_BUF_SIZE)];
+	char sym[const_max(2*RSRC_BUF_SIZE + DECODED_BUF_SIZE,
+			   2*RSRC_BUF_SIZE + FLAG_BUF_SIZE + RAW_BUF_SIZE)];
 
 	char *p = sym, *pend = sym + sizeof(sym);
 	int decode = (fmt[0] == 'R') ? 1 : 0;
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index dc5edc8f7564..fad6f989004e 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -46,7 +46,7 @@
 #include <net/sock.h>
 #include <net/raw.h>
 
-#define TCPUDP_MIB_MAX max_t(u32, UDP_MIB_MAX, TCP_MIB_MAX)
+#define TCPUDP_MIB_MAX const_max(UDP_MIB_MAX, TCP_MIB_MAX)
 
 /*
  *	Report socket allocation statistics [mea@utu.fi]
@@ -404,7 +404,7 @@ static int snmp_seq_show_tcp_udp(struct seq_file *seq, void *v)
 	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 +421,7 @@ 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 +432,7 @@ 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..58bbfc4fa7fa 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 const_max(const_max(UDP_MIB_MAX, TCP_MIB_MAX), \
+			       const_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