[PATCH v2] cxl: Fix null pointer dereference in cxl_get_fd

[PATCH v2] cxl: Fix null pointer dereference in cxl_get_fd

[Kunwu Chan]

kasprintf() returns a pointer to dynamically allocated memory
which can be NULL upon failure.

Uniformly handle resource release in error paths. And when an
error occurs, an error pointer should be returned.

Fixes: bdecf76e319a ("cxl: Fix coredump generation when cxl_get_fd() is used")
Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
Cc: Kunwu Chan <kunwu.chan@hotmail.com>
Suggested-by: Frederic Barrat <fbarrat@linux.ibm.com>
---
v2: Deal with error path
---
 drivers/misc/cxl/api.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/drivers/misc/cxl/api.c b/drivers/misc/cxl/api.c
index d85c56530863..b49bc3d29fc0 100644
--- a/drivers/misc/cxl/api.c
+++ b/drivers/misc/cxl/api.c
@@ -389,19 +389,22 @@ struct file *cxl_get_fd(struct cxl_context *ctx, struct file_operations *fops,
 			int *fd)
 {
 	struct file *file;
-	int rc, flags, fdtmp;
+	int rc = 0, flags, fdtmp;
 	char *name = NULL;
 
 	/* only allow one per context */
-	if (ctx->mapping)
-		return ERR_PTR(-EEXIST);
+	if (ctx->mapping) {
+		rc = -EEXIST;
+		goto err;
+	}
 
 	flags = O_RDWR | O_CLOEXEC;
 
 	/* This code is similar to anon_inode_getfd() */
 	rc = get_unused_fd_flags(flags);
 	if (rc < 0)
-		return ERR_PTR(rc);
+		goto err;
+
 	fdtmp = rc;
 
 	/*
@@ -419,6 +422,10 @@ struct file *cxl_get_fd(struct cxl_context *ctx, struct file_operations *fops,
 		fops = (struct file_operations *)&afu_fops;
 
 	name = kasprintf(GFP_KERNEL, "cxl:%d", ctx->pe);
+	if (!name) {
+		rc = -ENOMEM;
+		goto err_fd;
+	}
 	file = cxl_getfile(name, fops, ctx, flags);
 	kfree(name);
 	if (IS_ERR(file))
@@ -430,6 +437,9 @@ struct file *cxl_get_fd(struct cxl_context *ctx, struct file_operations *fops,
 
 err_fd:
 	put_unused_fd(fdtmp);
+err:
+	if (rc < 0)
+		return ERR_PTR(rc);
 	return NULL;
 }
 EXPORT_SYMBOL_GPL(cxl_get_fd);
-- 
2.39.2

Re: [PATCH v2] cxl: Fix null pointer dereference in cxl_get_fd

[Andrew Donnellan]

On Fri, 2024-01-12 at 13:49 +0800, Kunwu Chan wrote:

> +err:
> +	if (rc < 0)
> +		return ERR_PTR(rc);
>  	return NULL;

I don't think there's a way for this NULL to ever get returned?

Apart from that it looks good:

Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>

-- 
Andrew Donnellan    OzLabs, ADL Canberra
ajd@linux.ibm.com   IBM Australia Limited

Re: [PATCH v2] cxl: Fix null pointer dereference in cxl_get_fd

[Frederic Barrat]

On 12/01/2024 06:49, Kunwu Chan wrote:
> kasprintf() returns a pointer to dynamically allocated memory
> which can be NULL upon failure.
> 
> Uniformly handle resource release in error paths. And when an
> error occurs, an error pointer should be returned.
> 
> Fixes: bdecf76e319a ("cxl: Fix coredump generation when cxl_get_fd() is used")
> Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
> Cc: Kunwu Chan <kunwu.chan@hotmail.com>
> Suggested-by: Frederic Barrat <fbarrat@linux.ibm.com>
> ---

Thanks!
Acked-by: Frederic Barrat <fbarrat@linux.ibm.com>

   Fred


> v2: Deal with error path
> ---
>   drivers/misc/cxl/api.c | 18 ++++++++++++++----
>   1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/misc/cxl/api.c b/drivers/misc/cxl/api.c
> index d85c56530863..b49bc3d29fc0 100644
> --- a/drivers/misc/cxl/api.c
> +++ b/drivers/misc/cxl/api.c
> @@ -389,19 +389,22 @@ struct file *cxl_get_fd(struct cxl_context *ctx, struct file_operations *fops,
>   			int *fd)
>   {
>   	struct file *file;
> -	int rc, flags, fdtmp;
> +	int rc = 0, flags, fdtmp;
>   	char *name = NULL;
>   
>   	/* only allow one per context */
> -	if (ctx->mapping)
> -		return ERR_PTR(-EEXIST);
> +	if (ctx->mapping) {
> +		rc = -EEXIST;
> +		goto err;
> +	}
>   
>   	flags = O_RDWR | O_CLOEXEC;
>   
>   	/* This code is similar to anon_inode_getfd() */
>   	rc = get_unused_fd_flags(flags);
>   	if (rc < 0)
> -		return ERR_PTR(rc);
> +		goto err;
> +
>   	fdtmp = rc;
>   
>   	/*
> @@ -419,6 +422,10 @@ struct file *cxl_get_fd(struct cxl_context *ctx, struct file_operations *fops,
>   		fops = (struct file_operations *)&afu_fops;
>   
>   	name = kasprintf(GFP_KERNEL, "cxl:%d", ctx->pe);
> +	if (!name) {
> +		rc = -ENOMEM;
> +		goto err_fd;
> +	}
>   	file = cxl_getfile(name, fops, ctx, flags);
>   	kfree(name);
>   	if (IS_ERR(file))
> @@ -430,6 +437,9 @@ struct file *cxl_get_fd(struct cxl_context *ctx, struct file_operations *fops,
>   
>   err_fd:
>   	put_unused_fd(fdtmp);
> +err:
> +	if (rc < 0)
> +		return ERR_PTR(rc);
>   	return NULL;
>   }
>   EXPORT_SYMBOL_GPL(cxl_get_fd);