rpmsg: char: Avoid double destroy of default endpoint

JIRA: https://issues.redhat.com/browse/RHEL-78824

commit 467233a
Author: Shengjiu Wang <shengjiu.wang@nxp.com>
Date:   Wed Sep 21 09:58:43 2022 +0800

    rpmsg: char: Avoid double destroy of default endpoint

    The rpmsg_dev_remove() in rpmsg_core is the place for releasing
    this default endpoint.

    So need to avoid destroying the default endpoint in
    rpmsg_chrdev_eptdev_destroy(), this should be the same as
    rpmsg_eptdev_release(). Otherwise there will be double destroy
    issue that ept->refcount report warning:

    refcount_t: underflow; use-after-free.

    Call trace:
     refcount_warn_saturate+0xf8/0x150
     virtio_rpmsg_destroy_ept+0xd4/0xec
     rpmsg_dev_remove+0x60/0x70

    The issue can be reproduced by stopping remoteproc before
    closing the /dev/rpmsgX.

    Fixes: bea9b79 ("rpmsg: char: Add possibility to use default endpoint of the rpmsg device")
    Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
    Reviewed-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
    Reviewed-by: Peng Fan <peng.fan@nxp.com>
    Cc: stable <stable@vger.kernel.org>
    Link: https://lore.kernel.org/r/1663725523-6514-1-git-send-email-shengjiu.wang@nxp.com
    Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>

Signed-off-by: Jared Kangas <jkangas@redhat.com>

Author: rh-jkangas

drivers/rpmsg/rpmsg_char.c

@@ -76,7 +76,9 @@ int rpmsg_chrdev_eptdev_destroy(struct device *dev, void *data)
 
 	mutex_lock(&eptdev->ept_lock);
 	if (eptdev->ept) {
-		rpmsg_destroy_ept(eptdev->ept);
+		/* The default endpoint is released by the rpmsg core */
+		if (!eptdev->default_ept)
+			rpmsg_destroy_ept(eptdev->ept);
 		eptdev->ept = NULL;
 	}
 	mutex_unlock(&eptdev->ept_lock);