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 <[email protected]> > ---
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
