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Subject: Re: [PATCH 1/2] topology: use bin_attribute to avoid buff overflow
To:     Greg KH <gregkh@linuxfoundation.org>,
        Tian Tao <tiantao6@hisilicon.com>
CC:     <linux-kernel@vger.kernel.org>, <akpm@linux-foundation.org>,
        <song.bao.hua@hisilicon.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Jonathan Cameron <jonathan.cameron@huawei.com>
References: <1622516210-10886-1-git-send-email-tiantao6@hisilicon.com>
 <1622516210-10886-2-git-send-email-tiantao6@hisilicon.com>
 <YLW+hZwoImx2wjwS@kroah.com>
From:   "tiantao (H)" <tiantao6@huawei.com>
Message-ID: <4c9c7c17-e8d1-d601-6262-8064293a06a9@huawei.com>
Date:   Wed, 2 Jun 2021 14:14:49 +0800
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在 2021/6/1 12:58, Greg KH 写道:
> On Tue, Jun 01, 2021 at 10:56:49AM +0800, Tian Tao wrote:
>> Reading sys/devices/system/cpu/cpuX/topology/ returns cpu topology.
>> However, the size of this file is limited to PAGE_SIZE because of the
>> limitation for sysfs attribute. so we use bin_attribute instead of
>> attribute to avoid NR_CPUS too big to cause buff overflow.
>>
>> This patch is based on the following discussion.
>> https://www.spinics.net/lists/linux-doc/msg95921.html
> Please use lore.kernel.org for links as we have no control over other
> sites to ensure that they will work in the future.  Use the message id
> in the link as well, so that if something were to happen to lore, we can
> figure it out.
>
> Also, you are modifying a bunch of different files here, do you mean to
> do it for all of them?
>
>> Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
>> ---
>>   drivers/base/topology.c | 115 ++++++++++++++++++++++++++----------------------
>>   include/linux/bitmap.h  |   3 ++
>>   include/linux/cpumask.h |  25 +++++++++++
>>   lib/bitmap.c            |  34 ++++++++++++++
>>   4 files changed, 125 insertions(+), 52 deletions(-)
>>
>> diff --git a/drivers/base/topology.c b/drivers/base/topology.c
>> index 4d254fc..013edbb 100644
>> --- a/drivers/base/topology.c
>> +++ b/drivers/base/topology.c
>> @@ -21,25 +21,27 @@ static ssize_t name##_show(struct device *dev,				\
>>   	return sysfs_emit(buf, "%d\n", topology_##name(dev->id));	\
>>   }
>>   
>> -#define define_siblings_show_map(name, mask)				\
>> -static ssize_t name##_show(struct device *dev,				\
>> -			   struct device_attribute *attr, char *buf)	\
>> -{									\
>> -	return cpumap_print_to_pagebuf(false, buf, topology_##mask(dev->id));\
>> +#define define_siblings_read_func(name, mask)					\
>> +static ssize_t name##_read(struct file *file, struct kobject *kobj,		\
>> +				  struct bin_attribute *attr, char *buf,	\
>> +				  loff_t off, size_t count)			\
>> +{										\
>> +	struct device *dev = kobj_to_dev(kobj);                                 \
>> +										\
>> +	return cpumap_print_to_buf(false, buf, topology_##mask(dev->id),	\
>> +				   off, count);                                 \
>> +}										\
>> +										\
>> +static ssize_t name##_list_read(struct file *file, struct kobject *kobj,	\
>> +				  struct bin_attribute *attr, char *buf,	\
>> +				  loff_t off, size_t count)			\
>> +{										\
>> +	struct device *dev = kobj_to_dev(kobj);					\
>> +										\
>> +	return cpumap_print_to_buf(true, buf, topology_##mask(dev->id),		\
>> +				   off, count);					\
>>   }
>>   
>> -#define define_siblings_show_list(name, mask)				\
>> -static ssize_t name##_list_show(struct device *dev,			\
>> -				struct device_attribute *attr,		\
>> -				char *buf)				\
>> -{									\
>> -	return cpumap_print_to_pagebuf(true, buf, topology_##mask(dev->id));\
>> -}
>> -
>> -#define define_siblings_show_func(name, mask)	\
>> -	define_siblings_show_map(name, mask);	\
>> -	define_siblings_show_list(name, mask)
>> -
>>   define_id_show_func(physical_package_id);
>>   static DEVICE_ATTR_RO(physical_package_id);
>>   
>> @@ -49,71 +51,80 @@ static DEVICE_ATTR_RO(die_id);
>>   define_id_show_func(core_id);
>>   static DEVICE_ATTR_RO(core_id);
>>   
>> -define_siblings_show_func(thread_siblings, sibling_cpumask);
>> -static DEVICE_ATTR_RO(thread_siblings);
>> -static DEVICE_ATTR_RO(thread_siblings_list);
>> +define_siblings_read_func(thread_siblings, sibling_cpumask);
>> +static BIN_ATTR_RO(thread_siblings, 0);
>> +static BIN_ATTR_RO(thread_siblings_list, 0);
>>   
>> -define_siblings_show_func(core_cpus, sibling_cpumask);
>> -static DEVICE_ATTR_RO(core_cpus);
>> -static DEVICE_ATTR_RO(core_cpus_list);
>> +define_siblings_read_func(core_cpus, sibling_cpumask);
>> +static BIN_ATTR_RO(core_cpus, 0);
>> +static BIN_ATTR_RO(core_cpus_list, 0);
>>   
>> -define_siblings_show_func(core_siblings, core_cpumask);
>> -static DEVICE_ATTR_RO(core_siblings);
>> -static DEVICE_ATTR_RO(core_siblings_list);
>> +define_siblings_read_func(core_siblings, core_cpumask);
>> +static BIN_ATTR_RO(core_siblings, 0);
>> +static BIN_ATTR_RO(core_siblings_list, 0);
>>   
>> -define_siblings_show_func(die_cpus, die_cpumask);
>> -static DEVICE_ATTR_RO(die_cpus);
>> -static DEVICE_ATTR_RO(die_cpus_list);
>> +define_siblings_read_func(die_cpus, die_cpumask);
>> +static BIN_ATTR_RO(die_cpus, 0);
>> +static BIN_ATTR_RO(die_cpus_list, 0);
>>   
>> -define_siblings_show_func(package_cpus, core_cpumask);
>> -static DEVICE_ATTR_RO(package_cpus);
>> -static DEVICE_ATTR_RO(package_cpus_list);
>> +define_siblings_read_func(package_cpus, core_cpumask);
>> +static BIN_ATTR_RO(package_cpus, 0);
>> +static BIN_ATTR_RO(package_cpus_list, 0);
>>   
>>   #ifdef CONFIG_SCHED_BOOK
>>   define_id_show_func(book_id);
>>   static DEVICE_ATTR_RO(book_id);
>> -define_siblings_show_func(book_siblings, book_cpumask);
>> -static DEVICE_ATTR_RO(book_siblings);
>> -static DEVICE_ATTR_RO(book_siblings_list);
>> +define_siblings_read_func(book_siblings, book_cpumask);
>> +static BIN_ATTR_RO(book_siblings, 0);
>> +static BIN_ATTR_RO(book_siblings_list, 0);
>>   #endif
>>   
>>   #ifdef CONFIG_SCHED_DRAWER
>>   define_id_show_func(drawer_id);
>>   static DEVICE_ATTR_RO(drawer_id);
>> -define_siblings_show_func(drawer_siblings, drawer_cpumask);
>> -static DEVICE_ATTR_RO(drawer_siblings);
>> -static DEVICE_ATTR_RO(drawer_siblings_list);
>> +define_siblings_read_func(drawer_siblings, drawer_cpumask);
>> +static BIN_ATTR_RO(drawer_siblings, 0);
>> +static BIN_ATTR_RO(drawer_siblings_list, 0);
>>   #endif
>>   
>> +static struct bin_attribute *bin_attrs[] = {
>> +	&bin_attr_core_cpus,
>> +	&bin_attr_core_cpus_list,
>> +	&bin_attr_thread_siblings,
>> +	&bin_attr_thread_siblings_list,
>> +	&bin_attr_core_siblings,
>> +	&bin_attr_core_siblings_list,
>> +	&bin_attr_die_cpus,
>> +	&bin_attr_die_cpus_list,
>> +	&bin_attr_package_cpus,
>> +	&bin_attr_package_cpus_list,
>> +#ifdef CONFIG_SCHED_BOOK
>> +	&bin_attr_book_siblings,
>> +	&bin_attr_book_siblings_list,
>> +#endif
>> +#ifdef CONFIG_SCHED_DRAWER
>> +	&bin_attr_drawer_siblings,
>> +	&bin_attr_drawer_siblings_list,
>> +#endif
>> +	NULL,
>> +};
>> +
>>   static struct attribute *default_attrs[] = {
>>   	&dev_attr_physical_package_id.attr,
>>   	&dev_attr_die_id.attr,
>>   	&dev_attr_core_id.attr,
>> -	&dev_attr_thread_siblings.attr,
>> -	&dev_attr_thread_siblings_list.attr,
>> -	&dev_attr_core_cpus.attr,
>> -	&dev_attr_core_cpus_list.attr,
>> -	&dev_attr_core_siblings.attr,
>> -	&dev_attr_core_siblings_list.attr,
>> -	&dev_attr_die_cpus.attr,
>> -	&dev_attr_die_cpus_list.attr,
>> -	&dev_attr_package_cpus.attr,
>> -	&dev_attr_package_cpus_list.attr,
>>   #ifdef CONFIG_SCHED_BOOK
>>   	&dev_attr_book_id.attr,
>> -	&dev_attr_book_siblings.attr,
>> -	&dev_attr_book_siblings_list.attr,
>>   #endif
>>   #ifdef CONFIG_SCHED_DRAWER
>>   	&dev_attr_drawer_id.attr,
>> -	&dev_attr_drawer_siblings.attr,
>> -	&dev_attr_drawer_siblings_list.attr,
>>   #endif
>>   	NULL
>>   };
>>   
>>   static const struct attribute_group topology_attr_group = {
>>   	.attrs = default_attrs,
>> +	.bin_attrs = bin_attrs,
>>   	.name = "topology"
>>   };
>>   
>> diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
>> index 70a9324..bc401bd9b 100644
>> --- a/include/linux/bitmap.h
>> +++ b/include/linux/bitmap.h
>> @@ -219,6 +219,9 @@ extern unsigned int bitmap_ord_to_pos(const unsigned long *bitmap, unsigned int
>>   extern int bitmap_print_to_pagebuf(bool list, char *buf,
>>   				   const unsigned long *maskp, int nmaskbits);
>>   
>> +extern int bitmap_print_to_buf(bool list, char *buf,
>> +			       const unsigned long *maskp, int nmaskbits, loff_t off, size_t count);
>> +
>>   #define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1)))
>>   #define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1)))
>>   
>> diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
>> index 383684e..e4810b3e 100644
>> --- a/include/linux/cpumask.h
>> +++ b/include/linux/cpumask.h
>> @@ -928,6 +928,31 @@ cpumap_print_to_pagebuf(bool list, char *buf, const struct cpumask *mask)
>>   				      nr_cpu_ids);
>>   }
>>   
>> +/**
>> + * cpumap_print_to_buf  - copies the cpumask into the buffer either
>> + *      as comma-separated list of cpus or hex values of cpumask
>> + * @list: indicates whether the cpumap must be list
>> + * @mask: the cpumask to copy
>> + * @buf: the buffer to copy into
>> + * @off: the offset that buffer to copy into
>> + * @count: the count thatbuffer to copy into
>> + *
>> + * the role of cpumap_print_to_buf and cpumap_print_to_pagebuf is
>> + * the same, the difference is that the second parameter of
>> + * bitmap_print_to_buf can be more than one pagesize.
>> + *
>> + * Returns the length of the (null-terminated) @buf string, zero if
>> + * nothing is copied.
>> + */
>> +
>> +static inline ssize_t
>> +cpumap_print_to_buf(bool list, char *buf, const struct cpumask *mask,
>> +		    loff_t off, size_t count)
>> +{
>> +	return bitmap_print_to_buf(list, buf, cpumask_bits(mask),
>> +				   nr_cpu_ids, off, count);
>> +}
>> +
>>   #if NR_CPUS <= BITS_PER_LONG
>>   #define CPU_MASK_ALL							\
>>   (cpumask_t) { {								\
>> diff --git a/lib/bitmap.c b/lib/bitmap.c
>> index 75006c4..5bf89f1 100644
>> --- a/lib/bitmap.c
>> +++ b/lib/bitmap.c
>> @@ -460,6 +460,40 @@ int bitmap_parse_user(const char __user *ubuf,
>>   EXPORT_SYMBOL(bitmap_parse_user);
>>   
>>   /**
>> + * bitmap_print_to_buf - convert bitmap to list or hex format ASCII string
>> + * @list: indicates whether the bitmap must be list
>> + * @buf: page aligned buffer into which string is placed
>> + * @maskp: pointer to bitmap to convert
>> + * @nmaskbits: size of bitmap, in bits
>> + * @off: offset in buf
>> + * @count: count that already output
>> + *
>> + * the role of bitmap_print_to_buf and bitmap_print_to_pagebuf is
>> + * the same, the difference is that the second parameter of
>> + * bitmap_print_to_buf can be more than one pagesize.
>> + */
>> +int bitmap_print_to_buf(bool list, char *buf, const unsigned long *maskp,
>> +			int nmaskbits, loff_t off, size_t count)
>> +{
>> +	int len, size;
>> +	void *data;
>> +	char *fmt = list ? "%*pbl\n" : "%*pb\n";
>> +
>> +	len = snprintf(NULL, 0, fmt, nmaskbits, maskp);
>> +
>> +	data = kvmalloc(len+1, GFP_KERNEL);
>> +	if (!data)
>> +		return -ENOMEM;
>> +
>> +	size = scnprintf(data, len+1, fmt, nmaskbits, maskp);
>> +	size = memory_read_from_buffer(buf, count, &off, data, size);
>> +	kvfree(data);
>> +
>> +	return size;
> Why is this so different from bitmap_print_to_pagebuf()?  Can't you just
> use this function as the "real" function and then change
> bitmap_print_to_pagebuf() to call it with a size of PAGE_SIZE?

Do you mean do following change, is that correct? :-)

+int bitmap_print_to_buf(bool list, char *buf, const unsigned long *maskp,
+                       int nmaskbits, loff_t off, size_t count)
+{
+       int len, size;
+       void *data;
+       const char *fmt = list ? "%*pbl\n" : "%*pb\n";
+
+       if (off == LLONG_MAX && count == PAGE_SIZE - offset_in_page(buf))
+               return scnprintf(buf, count, fmt, nmaskbits, maskp);
+
+       len = snprintf(NULL, 0, fmt, nmaskbits, maskp);
+
+       data = kvmalloc(len+1, GFP_KERNEL);
+       if (!data)
+               return -ENOMEM;
+
+       size = scnprintf(data, len+1, fmt, nmaskbits, maskp);
+
+       size = memory_read_from_buffer(buf, count, &off, data, size);
+       kvfree(data);
+
+       return size;
+}
+EXPORT_SYMBOL(bitmap_print_to_buf);
+
+/**
   * bitmap_print_to_pagebuf - convert bitmap to list or hex format 
ASCII string
   * @list: indicates whether the bitmap must be list
   * @buf: page aligned buffer into which string is placed
@@ -480,8 +518,8 @@ int bitmap_print_to_pagebuf(bool list, char *buf, 
const unsigned long *maskp,
  {
         ptrdiff_t len = PAGE_SIZE - offset_in_page(buf);

-       return list ? scnprintf(buf, len, "%*pbl\n", nmaskbits, maskp) :
-                     scnprintf(buf, len, "%*pb\n", nmaskbits, maskp);
+       return bitmap_print_to_buf(list, buf, maskp, nmaskbits,
+                                  LLONG_MAX, len);
  }

>
> Can you add the new function as the first patch in the series and then
> use it in the later ones?  That makes it easier to review on its own.
>
> thanks,
>
> greg k-h
> .
>