bridge: fix potential snprintf overflow

There is a theoretical snprintf overflow in bridge slave bitmask
print code found by CodeQL scan.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

diff --git a/ip/iplink_bridge_slave.c b/ip/iplink_bridge_slave.c
index dc73c86574dacb223b04074820e28c186c63a9f8..3821923b5da5cd8028ceed89f50ee72d0ab428e0 100644 (file)
--- a/ip/iplink_bridge_slave.c
+++ b/ip/iplink_bridge_slave.c
@@ -100,13 +100,20 @@ static void _bitmask2str(__u16 bitmask, char *dst, size_t dst_size,
        int len, i;
 
        for (i = 0, len = 0; bitmask; i++, bitmask >>= 1) {
+               int n;
+
                if (bitmask & 0x1) {
                        if (tbl[i])
-                               len += snprintf(dst + len, dst_size - len, "%s,",
+                               n = snprintf(dst + len, dst_size - len, "%s,",
                                                tbl[i]);
                        else
-                               len += snprintf(dst + len, dst_size - len, "0x%x,",
+                               n = snprintf(dst + len, dst_size - len, "0x%x,",
                                                (1 << i));
+
+                       if (n < 0 || n >= dst_size - len)
+                               break;
+
+                       len += n;
                }
        }