isdn/gigaset: limit raw CAPI message dump length

In dump_rawmsg, the length field from a received data package was
used unscrutinized, allowing an attacker to control the size of the
allocated buffer and the number of times the output loop iterates.
Fix by limiting to a reasonable value.

Spotted with Coverity.
Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/gigaset/capi.c

@@ -250,6 +250,8 @@ static inline void dump_rawmsg(enum debuglevel level, const char *tag,
 	l -= 12;
 	if (l <= 0)
 		return;
+	if (l > 64)
+		l = 64; /* arbitrary limit */
 	dbgline = kmalloc(3 * l, GFP_ATOMIC);
 	if (!dbgline)
 		return;