[PATCH v1] rpmsg: char: fix use-after-free on probe error path

[Yuho Choi <dbgh9129@gmail.com>]

rpmsg_chrdev_probe() stores the newly allocated eptdev in the default
endpoint's priv pointer before calling rpmsg_chrdev_eptdev_add(). If
rpmsg_chrdev_eptdev_add() then fails, its error path frees eptdev while
the default endpoint may still dispatch inbound messages through
rpmsg_ept_cb(), leaving the callback with a dangling priv pointer.

Avoid publishing eptdev through the default endpoint until
rpmsg_chrdev_eptdev_add() succeeds. Any message that arrives before the
priv is published should be ignored, so make rpmsg_ept_cb() return
success when priv is NULL.

Fixes: bc69d10665690 ("rpmsg: char: Introduce the "rpmsg-raw" channel")
Signed-off-by: Yuho Choi <dbgh9129@gmail.com>
---
 drivers/rpmsg/rpmsg_char.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
index ca9cf8858a5ef..549a24b70884d 100644
--- a/drivers/rpmsg/rpmsg_char.c
+++ b/drivers/rpmsg/rpmsg_char.c
@@ -11,6 +11,7 @@
  * was based on TI & Google OMX rpmsg driver.
  */
 
+#include "asm-generic/rwonce.h"
 #define pr_fmt(fmt)	KBUILD_MODNAME ": " fmt
 
 #include <linux/cdev.h>
@@ -104,6 +105,9 @@ static int rpmsg_ept_cb(struct rpmsg_device *rpdev, void *buf, int len,
 	struct rpmsg_eptdev *eptdev = priv;
 	struct sk_buff *skb;
 
+	if (!eptdev)
+		return 0;
+
 	skb = alloc_skb(len, GFP_ATOMIC);
 	if (!skb)
 		return -ENOMEM;
@@ -490,6 +494,7 @@ static int rpmsg_chrdev_probe(struct rpmsg_device *rpdev)
 	struct rpmsg_channel_info chinfo;
 	struct rpmsg_eptdev *eptdev;
 	struct device *dev = &rpdev->dev;
+	int ret;
 
 	memcpy(chinfo.name, rpdev->id.name, RPMSG_NAME_SIZE);
 	chinfo.src = rpdev->src;
@@ -502,13 +507,17 @@ static int rpmsg_chrdev_probe(struct rpmsg_device *rpdev)
 	/* Set the default_ept to the rpmsg device endpoint */
 	eptdev->default_ept = rpdev->ept;
 
+	ret = rpmsg_chrdev_eptdev_add(eptdev, chinfo);
+
+	if (ret)
+		return ret;
 	/*
 	 * The rpmsg_ept_cb uses *priv parameter to get its rpmsg_eptdev context.
-	 * Storedit in default_ept *priv field.
+	 * Stored it in default_ept *priv field.
 	 */
 	eptdev->default_ept->priv = eptdev;
 
-	return rpmsg_chrdev_eptdev_add(eptdev, chinfo);
+	return 0;
 }
 
 static void rpmsg_chrdev_remove(struct rpmsg_device *rpdev)
-- 
2.50.1 (Apple Git-155)