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

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

[Yuho Choi]

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)

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

[Mathieu Poirier]

Good morning,

On Thu, Apr 16, 2026 at 12:23:38AM -0400, Yuho Choi wrote:
> 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")

The SHA should be 12 characters.

> 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"

Why is this needed?

>  #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;
> +

If this is needed, the same check is probably needed in rpmsg_ept_flow_cb().

Thanks,
Mathieu

>  	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)
> 

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

[kernel test robot]

Hi Yuho,

kernel test robot noticed the following build warnings:

[auto build test WARNING on remoteproc/rpmsg-next]
[also build test WARNING on linus/master v7.0 next-20260422]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Yuho-Choi/rpmsg-char-fix-use-after-free-on-probe-error-path/20260421-073128
base:   https://git.kernel.org/pub/scm/linux/kernel/git/remoteproc/linux.git rpmsg-next
patch link:    https://lore.kernel.org/r/20260416042338.10146-1-dbgh9129%40gmail.com
patch subject: [PATCH v1] rpmsg: char: fix use-after-free on probe error path
config: alpha-allyesconfig (https://download.01.org/0day-ci/archive/20260422/202604222350.v3J2LzRi-lkp@intel.com/config)
compiler: alpha-linux-gcc (GCC) 15.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260422/202604222350.v3J2LzRi-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202604222350.v3J2LzRi-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from include/linux/compiler.h:372,
                    from include/linux/build_bug.h:5,
                    from include/linux/container_of.h:5,
                    from include/linux/list.h:5,
                    from include/linux/kobject.h:19,
                    from include/linux/cdev.h:5,
                    from drivers/rpmsg/rpmsg_char.c:17:
>> arch/alpha/include/asm/rwonce.h:23:9: warning: '__READ_ONCE' redefined
      23 | #define __READ_ONCE(x)                                                  \
         |         ^~~~~~~~~~~
   In file included from drivers/rpmsg/rpmsg_char.c:14:
   include/asm-generic/rwonce.h:44:9: note: this is the location of the previous definition
      44 | #define __READ_ONCE(x)  (*(const volatile __unqual_scalar_typeof(x) *)&(x))
         |         ^~~~~~~~~~~


vim +/__READ_ONCE +23 arch/alpha/include/asm/rwonce.h

d6462858851549c Will Deacon 2019-10-30  11  
d6462858851549c Will Deacon 2019-10-30  12  /*
d6462858851549c Will Deacon 2019-10-30  13   * Alpha is apparently daft enough to reorder address-dependent loads
d6462858851549c Will Deacon 2019-10-30  14   * on some CPU implementations. Knock some common sense into it with
d6462858851549c Will Deacon 2019-10-30  15   * a memory barrier in READ_ONCE().
d6462858851549c Will Deacon 2019-10-30  16   *
d6462858851549c Will Deacon 2019-10-30  17   * For the curious, more information about this unusual reordering is
d6462858851549c Will Deacon 2019-10-30  18   * available in chapter 15 of the "perfbook":
d6462858851549c Will Deacon 2019-10-30  19   *
d6462858851549c Will Deacon 2019-10-30  20   *  https://kernel.org/pub/linux/kernel/people/paulmck/perfbook/perfbook.html
d6462858851549c Will Deacon 2019-10-30  21   *
d6462858851549c Will Deacon 2019-10-30  22   */
d6462858851549c Will Deacon 2019-10-30 @23  #define __READ_ONCE(x)							\
d6462858851549c Will Deacon 2019-10-30  24  ({									\
d6462858851549c Will Deacon 2019-10-30  25  	__unqual_scalar_typeof(x) __x =					\
d6462858851549c Will Deacon 2019-10-30  26  		(*(volatile typeof(__x) *)(&(x)));			\
d6462858851549c Will Deacon 2019-10-30  27  	mb();								\
d6462858851549c Will Deacon 2019-10-30  28  	(typeof(x))__x;							\
d6462858851549c Will Deacon 2019-10-30  29  })
d6462858851549c Will Deacon 2019-10-30  30  

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https://github.com/intel/lkp-tests/wiki