kdb: Use format-specifiers rather than memset() for padding in kdb_re…

…ad()

commit c9b51ddb66b1d96e4d364c088da0f1dfb004c574 upstream.

Currently when the current line should be removed from the display
kdb_read() uses memset() to fill a temporary buffer with spaces.
The problem is not that this could be trivially implemented using a
format string rather than open coding it. The real problem is that
it is possible, on systems with a long kdb_prompt_str, to write past
the end of the tmpbuffer.

Happily, as mentioned above, this can be trivially implemented using a
format string. Make it so!

Cc: [email protected]
Reviewed-by: Douglas Anderson <[email protected]>
Tested-by: Justin Stitt <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Daniel Thompson <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

kernel/debug/kdb/kdb_io.c

@@ -324,11 +324,9 @@ static char *kdb_read(char *buffer, size_t bufsize)
 		break;
 	case 14: /* Down */
 	case 16: /* Up */
-		memset(tmpbuffer, ' ',
-		       strlen(kdb_prompt_str) + (lastchar-buffer));
-		*(tmpbuffer+strlen(kdb_prompt_str) +
-		  (lastchar-buffer)) = '\0';
-		kdb_printf("\r%s\r", tmpbuffer);
+		kdb_printf("\r%*c\r",
+			   (int)(strlen(kdb_prompt_str) + (lastchar - buffer)),
+			   ' ');
 		*lastchar = (char)key;
 		*(lastchar+1) = '\0';
 		return lastchar;