net: dsa: vsc73xx: replace deprecated strncpy with ethtool_sprintf

`strncpy` is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

ethtool_sprintf() is designed specifically for get_strings() usage.
Let's replace strncpy in favor of this more robust and easier to
understand interface.

This change could result in misaligned strings when if(cnt) fails. To
combat this, use ternary to place empty string in buffer and properly
increment pointer to next string slot.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
Link: https://github.com/KSPP/linux/issues/90
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20231010-strncpy-drivers-net-dsa-vitesse-vsc73xx-core-c-v2-1-ba4416a9ff23@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/dsa/vitesse-vsc73xx-core.c b/drivers/net/dsa/vitesse-vsc73xx-core.c
index 35a846d7e13f47ecfd8e18027df42d5e0fdbd4fe..e6f29e4e508c1e0e848920c88470aeedfba2e119 100644 (file)
--- a/drivers/net/dsa/vitesse-vsc73xx-core.c
+++ b/drivers/net/dsa/vitesse-vsc73xx-core.c
@@ -928,7 +928,8 @@ static void vsc73xx_get_strings(struct dsa_switch *ds, int port, u32 stringset,
        const struct vsc73xx_counter *cnt;
        struct vsc73xx *vsc = ds->priv;
        u8 indices[6];
-       int i, j;
+       u8 *buf = data;
+       int i;
        u32 val;
        int ret;
 
@@ -948,10 +949,7 @@ static void vsc73xx_get_strings(struct dsa_switch *ds, int port, u32 stringset,
        indices[5] = ((val >> 26) & 0x1f); /* TX counter 2 */
 
        /* The first counters is the RX octets */
-       j = 0;
-       strncpy(data + j * ETH_GSTRING_LEN,
-               "RxEtherStatsOctets", ETH_GSTRING_LEN);
-       j++;
+       ethtool_sprintf(&buf, "RxEtherStatsOctets");
 
        /* Each port supports recording 3 RX counters and 3 TX counters,
         * figure out what counters we use in this set-up and return the
@@ -961,23 +959,16 @@ static void vsc73xx_get_strings(struct dsa_switch *ds, int port, u32 stringset,
         */
        for (i = 0; i < 3; i++) {
                cnt = vsc73xx_find_counter(vsc, indices[i], false);
-               if (cnt)
-                       strncpy(data + j * ETH_GSTRING_LEN,
-                               cnt->name, ETH_GSTRING_LEN);
-               j++;
+               ethtool_sprintf(&buf, "%s", cnt ? cnt->name : "");
        }
 
        /* TX stats begins with the number of TX octets */
-       strncpy(data + j * ETH_GSTRING_LEN,
-               "TxEtherStatsOctets", ETH_GSTRING_LEN);
-       j++;
+       ethtool_sprintf(&buf, "TxEtherStatsOctets");
 
        for (i = 3; i < 6; i++) {
                cnt = vsc73xx_find_counter(vsc, indices[i], true);
-               if (cnt)
-                       strncpy(data + j * ETH_GSTRING_LEN,
-                               cnt->name, ETH_GSTRING_LEN);
-               j++;
+               ethtool_sprintf(&buf, "%s", cnt ? cnt->name : "");
+
        }
 }