[PATCH v3 4/4] ax.25: Remove the now superfluous sentinel elements from ctl_table array

[Joel Granados via B4 Relay]

From: Joel Granados <j.granados@xxxxxxxxxxx>

This commit comes at the tail end of a greater effort to remove the
empty elements at the end of the ctl_table arrays (sentinels) which will
reduce the overall build time size of the kernel and run time memory
bloat by ~64 bytes per sentinel (further information Link :
https://lore.kernel.org/all/ZO5Yx5JFogGi%2FcBo@xxxxxxxxxxxxxxxxxxxxxx/)

Avoid a buffer overflow when traversing the ctl_table by ensuring that
AX25_MAX_VALUES is the same as the size of ax25_param_table. This is
done with a BUILD_BUG_ON where ax25_param_table is defined and a
CONFIG_AX25_DAMA_SLAVE guard in the unnamed enum definition as well as
in the ax25_dev_device_up and ax25_ds_set_timer functions.

The overflow happened when the sentinel was removed from
ax25_param_table. The sentinel's data element was changed when
CONFIG_AX25_DAMA_SLAVE was undefined. This had no adverse effects as it
still stopped on the sentinel's null procname but needed to be addressed
once the sentinel was removed.

Signed-off-by: Joel Granados <j.granados@xxxxxxxxxxx>
---
 include/net/ax25.h         | 2 ++
 net/ax25/ax25_dev.c        | 3 +++
 net/ax25/ax25_ds_timer.c   | 4 ++++
 net/ax25/sysctl_net_ax25.c | 3 +--
 4 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/net/ax25.h b/include/net/ax25.h
index 0d939e5aee4e..eb9cee8252c8 100644
--- a/include/net/ax25.h
+++ b/include/net/ax25.h
@@ -139,7 +139,9 @@ enum {
 	AX25_VALUES_N2,		/* Default N2 value */
 	AX25_VALUES_PACLEN,	/* AX.25 MTU */
 	AX25_VALUES_PROTOCOL,	/* Std AX.25, DAMA Slave, DAMA Master */
+#ifdef CONFIG_AX25_DAMA_SLAVE
 	AX25_VALUES_DS_TIMEOUT,	/* DAMA Slave timeout */
+#endif
 	AX25_MAX_VALUES		/* THIS MUST REMAIN THE LAST ENTRY OF THIS LIST */
 };
 
diff --git a/net/ax25/ax25_dev.c b/net/ax25/ax25_dev.c
index c5462486dbca..af547e185a94 100644
--- a/net/ax25/ax25_dev.c
+++ b/net/ax25/ax25_dev.c
@@ -78,7 +78,10 @@ void ax25_dev_device_up(struct net_device *dev)
 	ax25_dev->values[AX25_VALUES_N2]        = AX25_DEF_N2;
 	ax25_dev->values[AX25_VALUES_PACLEN]	= AX25_DEF_PACLEN;
 	ax25_dev->values[AX25_VALUES_PROTOCOL]  = AX25_DEF_PROTOCOL;
+
+#ifdef CONFIG_AX25_DAMA_SLAVE
 	ax25_dev->values[AX25_VALUES_DS_TIMEOUT]= AX25_DEF_DS_TIMEOUT;
+#endif
 
 #if defined(CONFIG_AX25_DAMA_SLAVE) || defined(CONFIG_AX25_DAMA_MASTER)
 	ax25_ds_setup_timer(ax25_dev);
diff --git a/net/ax25/ax25_ds_timer.c b/net/ax25/ax25_ds_timer.c
index c4f8adbf8144..8f385d2a7628 100644
--- a/net/ax25/ax25_ds_timer.c
+++ b/net/ax25/ax25_ds_timer.c
@@ -49,12 +49,16 @@ void ax25_ds_del_timer(ax25_dev *ax25_dev)
 
 void ax25_ds_set_timer(ax25_dev *ax25_dev)
 {
+#ifdef CONFIG_AX25_DAMA_SLAVE
 	if (ax25_dev == NULL)		/* paranoia */
 		return;
 
 	ax25_dev->dama.slave_timeout =
 		msecs_to_jiffies(ax25_dev->values[AX25_VALUES_DS_TIMEOUT]) / 10;
 	mod_timer(&ax25_dev->dama.slave_timer, jiffies + HZ);
+#else
+	return;
+#endif
 }
 
 /*
diff --git a/net/ax25/sysctl_net_ax25.c b/net/ax25/sysctl_net_ax25.c
index db66e11e7fe8..fb9966926e90 100644
--- a/net/ax25/sysctl_net_ax25.c
+++ b/net/ax25/sysctl_net_ax25.c
@@ -141,8 +141,6 @@ static const struct ctl_table ax25_param_table[] = {
 		.extra2		= &max_ds_timeout
 	},
 #endif
-
-	{ }	/* that's all, folks! */
 };
 
 int ax25_register_dev_sysctl(ax25_dev *ax25_dev)
@@ -155,6 +153,7 @@ int ax25_register_dev_sysctl(ax25_dev *ax25_dev)
 	if (!table)
 		return -ENOMEM;
 
+	BUILD_BUG_ON(AX25_MAX_VALUES != ARRAY_SIZE(ax25_param_table));
 	for (k = 0; k < AX25_MAX_VALUES; k++)
 		table[k].data = &ax25_dev->values[k];
 

-- 
2.43.0