Re: [PATCH] of: Add printf '%pOFm' for generating modalias

[quic_zijuhu <quic_zijuhu@quicinc.com>]

On 12/18/2024 2:37 AM, Rob Herring (Arm) wrote:
> The callers for of_modalias() generally need the module alias as part of
> some larger string. That results in some error prone manipulation of the
> buffer prepend/append the module alias string. In fact,
> of_device_uevent_modalias() has several issues. First, it's off by one
> too few characters in utilization of the full buffer. Second, the error
> paths leave OF_MODALIAS with a truncated value when in the end nothing
> should be added to the buffer. It is also fragile because it needs
> internal details of struct kobj_uevent_env. add_uevent_var() really
> wants to write the env variable and value in one shot which would need
> either a temporary buffer for value or a format specifier.
> 
> Fix these issues by adding a new printf format specifier, "%pOFm". With
> the format specifier in place, simplify all the callers of
> of_modalias(). of_modalias() can also be simplified with vsprintf()
> being the only caller as it avoids the error conditions.
> 

good solution (^^).

> Cc: Zijun Hu <quic_zijuhu@quicinc.com>
> Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
> ---
>  Documentation/core-api/printk-formats.rst |  1 +
>  drivers/of/device.c                       | 25 ++--------------
>  drivers/of/module.c                       | 35 +++++------------------
>  drivers/of/unittest.c                     |  2 ++
>  include/linux/of.h                        |  8 +++---
>  lib/vsprintf.c                            |  7 +++--
>  6 files changed, 22 insertions(+), 56 deletions(-)
> 
> diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
> index ecccc0473da9..d72fe3d8c427 100644
> --- a/Documentation/core-api/printk-formats.rst
> +++ b/Documentation/core-api/printk-formats.rst
> @@ -496,6 +496,7 @@ equivalent to %pOFf.
>  	- F - device node flags
>  	- c - major compatible string
>  	- C - full compatible string
> +	- m - module alias string

Ack.

>  
>  The separator when using multiple arguments is ':'
>  
> diff --git a/drivers/of/device.c b/drivers/of/device.c
> index edf3be197265..ae8c47d5db8e 100644
> --- a/drivers/of/device.c
> +++ b/drivers/of/device.c
> @@ -199,14 +199,9 @@ ssize_t of_device_modalias(struct device *dev, char *str, ssize_t len)
>  	if (!dev || !dev->of_node || dev->of_node_reused)
>  		return -ENODEV;
>  
> -	sl = of_modalias(dev->of_node, str, len - 2);
> -	if (sl < 0)
> -		return sl;
> -	if (sl > len - 2)
> +	sl = snprintf(str, len, "%pOFm\n", dev->of_node);
> +	if (sl >= len)
>  		return -ENOMEM;
> -
> -	str[sl++] = '\n';
> -	str[sl] = 0;
>  	return sl;
>  }

Ack.

>  EXPORT_SYMBOL_GPL(of_device_modalias);
> @@ -256,24 +251,10 @@ EXPORT_SYMBOL_GPL(of_device_uevent);
>  
>  int of_device_uevent_modalias(const struct device *dev, struct kobj_uevent_env *env)
>  {
> -	int sl;
> -
>  	if ((!dev) || (!dev->of_node) || dev->of_node_reused)
>  		return -ENODEV;
>  
> -	/* Devicetree modalias is tricky, we add it in 2 steps */
> -	if (add_uevent_var(env, "MODALIAS="))
> -		return -ENOMEM;
> -
> -	sl = of_modalias(dev->of_node, &env->buf[env->buflen-1],
> -			 sizeof(env->buf) - env->buflen);
> -	if (sl < 0)
> -		return sl;
> -	if (sl >= (sizeof(env->buf) - env->buflen))
> -		return -ENOMEM;
> -	env->buflen += sl;
> -
> -	return 0;
> +	return add_uevent_var(env, "MODALIAS=%pOFm", dev->of_node);
>  }

Ack.

>  EXPORT_SYMBOL_GPL(of_device_uevent_modalias);
>  
> diff --git a/drivers/of/module.c b/drivers/of/module.c
> index 1e735fc130ad..80879d2abea8 100644
> --- a/drivers/of/module.c
> +++ b/drivers/of/module.c
> @@ -8,21 +8,14 @@
>  #include <linux/slab.h>
>  #include <linux/string.h>
>  
> -ssize_t of_modalias(const struct device_node *np, char *str, ssize_t len)
> +/* Do not use directly, use %pOFm format specifier instead */
> +size_t of_modalias(const struct device_node *np, char *str, size_t len)
>  {
>  	const char *compat;
>  	char *c;
>  	struct property *p;
> -	ssize_t csize;
> -	ssize_t tsize;
> -
> -	/*
> -	 * Prevent a kernel oops in vsnprintf() -- it only allows passing a
> -	 * NULL ptr when the length is also 0. Also filter out the negative
> -	 * lengths...
> -	 */
> -	if ((len > 0 && !str) || len < 0)
> -		return -EINVAL;
> +	size_t csize;
> +	size_t tsize;
> 

Ack.

>  	/* Name & Type */
>  	/* %p eats all alphanum characters, so %c must be used here */
> @@ -53,29 +46,15 @@ ssize_t of_modalias(const struct device_node *np, char *str, ssize_t len)
>  
>  int of_request_module(const struct device_node *np)
>  {
> -	char *str;
> -	ssize_t size;
> -	int ret;
> +	char *str __free(kfree);

char *str __free(kfree) = NULL;

otherwise, wild pointer dereference may happen when return below.

>  
>  	if (!np)
>  		return -ENODEV;
>  
> -	size = of_modalias(np, NULL, 0);
> -	if (size < 0)
> -		return size;
> -
> -	/* Reserve an additional byte for the trailing '\0' */
> -	size++;
> -
> -	str = kmalloc(size, GFP_KERNEL);
> +	str = kasprintf(GFP_KERNEL, "%pOFm", np);
>  	if (!str)
>  		return -ENOMEM;
>  
> -	of_modalias(np, str, size);
> -	str[size - 1] = '\0';
> -	ret = request_module(str);
> -	kfree(str);
> -
> -	return ret;
> +	return request_module(str);

Ack.

>  }
>  EXPORT_SYMBOL_GPL(of_request_module);
> diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
> index daf9a2dddd7e..93921399f02d 100644
> --- a/drivers/of/unittest.c
> +++ b/drivers/of/unittest.c
> @@ -342,6 +342,8 @@ static void __init of_unittest_printf(void)
>  	of_unittest_printf_one(np, "%pOFc", "test-sub-device");
>  	of_unittest_printf_one(np, "%pOFC",
>  			"\"test-sub-device\",\"test-compat2\",\"test-compat3\"");
> +	of_unittest_printf_one(np, "%pOFm",
> +			"of:NdevT(null)Ctest-sub-deviceCtest-compat2Ctest-compat3");
>  }
>  
>  struct node_hash {
> diff --git a/include/linux/of.h b/include/linux/of.h
> index f921786cb8ac..9fe7d17ce7e2 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -382,7 +382,7 @@ extern int of_count_phandle_with_args(const struct device_node *np,
>  	const char *list_name, const char *cells_name);
>  
>  /* module functions */
> -extern ssize_t of_modalias(const struct device_node *np, char *str, ssize_t len);
> +extern size_t of_modalias(const struct device_node *np, char *str, size_t len);

extern  may be removed. it does not matter to keep it here as well.

Ack.


>  extern int of_request_module(const struct device_node *np);
>  
>  /* phandle iterator functions */
> @@ -762,10 +762,10 @@ static inline int of_count_phandle_with_args(const struct device_node *np,
>  	return -ENOSYS;
>  }
>  
> -static inline ssize_t of_modalias(const struct device_node *np, char *str,
> -				  ssize_t len)
> +static inline size_t of_modalias(const struct device_node *np, char *str,
> +				 size_t len)
>  {
> -	return -ENODEV;
> +	return 0;
>  }
>  

Ack.

>  static inline int of_request_module(const struct device_node *np)
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 9d3dac38a3f4..6a4f99b39de0 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -2169,10 +2169,10 @@ char *device_node_string(char *buf, char *end, struct device_node *dn,
>  
>  	/* simple case without anything any more format specifiers */
>  	fmt++;
> -	if (fmt[0] == '\0' || strcspn(fmt,"fnpPFcC") > 0)
> +	if (fmt[0] == '\0' || strcspn(fmt,"fnpPFcCm") > 0)
>  		fmt = "f";
>  
> -	for (pass = false; strspn(fmt,"fnpPFcC"); fmt++, pass = true) {
> +	for (pass = false; strspn(fmt,"fnpPFcCm"); fmt++, pass = true) {
>  		int precision;
>  		if (pass) {
>  			if (buf < end)
> @@ -2226,6 +2226,9 @@ char *device_node_string(char *buf, char *end, struct device_node *dn,
>  				has_mult = true;
>  			}
>  			break;
> +		case 'm':
> +			buf += of_modalias(dn, buf, end - buf);
> +			break;
>  		default:
>  			break;
>  		}

may Add below tag if the only issue is solved.

Reviewed-by: Zijun Hu <quic_zijuhu@quicinc.com>