Re: [PATCH] sysfs: Add sysfs_emit to replace sprintf to PAGE_SIZE buffers.

From: Denis Efremov
Date: Sat Aug 29 2020 - 03:02:47 EST


Hi,

On 8/29/20 1:52 AM, Joe Perches wrote:
> sprintf does not know the PAGE_SIZE maximum of the temporary buffer
> used for outputting sysfs content requests and it's possible to
> overrun the buffer length.
>
> Add a generic sysfs_emit mechanism that knows that the size of the
> temporary buffer and ensures that no overrun is done.
>
> Signed-off-by: Joe Perches <joe@xxxxxxxxxxx>
> ---


It could be a good idea to update the docs to, i.e.:
https://www.kernel.org/doc/html/latest/filesystems/sysfs.html


> fs/sysfs/file.c | 30 ++++++++++++++++++++++++++++++
> include/linux/sysfs.h | 8 ++++++++
> 2 files changed, 38 insertions(+)
>
> diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
> index eb6897ab78e7..06a13bbd7080 100644
> --- a/fs/sysfs/file.c
> +++ b/fs/sysfs/file.c
> @@ -707,3 +707,33 @@ int sysfs_change_owner(struct kobject *kobj, kuid_t kuid, kgid_t kgid)
> return 0;
> }
> EXPORT_SYMBOL_GPL(sysfs_change_owner);
> +
> +/**
> + * sysfs_emit - scnprintf equivalent, aware of PAGE_SIZE buffer.
> + * @buf: start of PAGE_SIZE buffer.
> + * @pos: current position in buffer
> + * (pos - buf) must always be < PAGE_SIZE
> + * @fmt: format
> + * @...: arguments to format
> + *
> + *
> + * Returns number of characters written at pos.
> + */
> +int sysfs_emit(char *buf, char *pos, const char *fmt, ...)
> +{
> + va_list args;
> + bool bad_pos = pos < buf;
> + bool bad_len = (pos - buf) >= PAGE_SIZE;
> + int len;
> +
> + if (WARN(bad_pos || bad_len, "(pos < buf):%d (pos >= PAGE_SIZE):%d\n",
> + bad_pos, bad_len))
> + return 0;
> +
> + va_start(args, fmt);
> + len = vscnprintf(pos, PAGE_SIZE - (pos - buf), fmt, args);
> + va_end(args);
> +
> + return len;
> +}
> +EXPORT_SYMBOL_GPL(sysfs_emit);
> diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
> index 34e84122f635..5a21d3d30016 100644
> --- a/include/linux/sysfs.h
> +++ b/include/linux/sysfs.h
> @@ -329,6 +329,8 @@ int sysfs_groups_change_owner(struct kobject *kobj,
> int sysfs_group_change_owner(struct kobject *kobj,
> const struct attribute_group *groups, kuid_t kuid,
> kgid_t kgid);
> +__printf(3, 4)
> +int sysfs_emit(char *buf, char *pos, const char *fmt, ...);
>
> #else /* CONFIG_SYSFS */
>
> @@ -576,6 +578,12 @@ static inline int sysfs_group_change_owner(struct kobject *kobj,
> return 0;
> }
>
> +__printf(3, 4)
> +static inline int sysfs_emit(char *buf, char *pos, const char *fmt, ...)
> +{
> + return 0;
> +}
> +
> #endif /* CONFIG_SYSFS */
>
> static inline int __must_check sysfs_create_file(struct kobject *kobj,
>

Thanks,
Denis