chardev: Fix record/replay error path NULL deref in device creation

qemu_chardev_set_replay() was being called in chardev creation to
set up replay parameters even if the chardev is NULL.

A segfault can be reproduced by specifying '-serial chardev:bad' with
an rr=record mode.

Fix this with a NULL pointer check.

Reported-by: Peter Maydell <[email protected]>
Resolves: Coverity CID 1559470
Fixes: 4c193bb ("chardev: set record/replay on the base device of a muxed device")
Signed-off-by: Nicholas Piggin <[email protected]>
Reviewed-by: Marc-André Lureau <[email protected]>
Reviewed-by: Peter Maydell <[email protected]>
Message-ID: <[email protected]>

Author: npiggin

chardev/char.c

@@ -726,7 +726,7 @@ static Chardev *__qemu_chr_new(const char *label, const char *filename,
 
     if (strstart(filename, "chardev:", &p)) {
         chr = qemu_chr_find(p);
-        if (replay) {
+        if (replay && chr) {
             qemu_chardev_set_replay(chr, &err);
             if (err) {
                 error_report_err(err);