Re: [PATCH v2 06/16] fanotify: pass optional file access range in pre-content event

[Josef Bacik <josef@toxicpanda.com>]

On Fri, Aug 09, 2024 at 02:00:29PM +0200, Christian Brauner wrote:
> On Thu, Aug 08, 2024 at 03:27:08PM GMT, Josef Bacik wrote:
> > From: Amir Goldstein <amir73il@gmail.com>
> > 
> > We would like to add file range information to pre-content events.
> > 
> > Pass a struct file_range with optional offset and length to event handler
> > along with pre-content permission event.
> > 
> > Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> > ---
> >  fs/notify/fanotify/fanotify.c    | 10 ++++++++--
> >  fs/notify/fanotify/fanotify.h    |  2 ++
> >  include/linux/fsnotify.h         | 17 ++++++++++++++++-
> >  include/linux/fsnotify_backend.h | 32 ++++++++++++++++++++++++++++++++
> >  4 files changed, 58 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> > index b163594843f5..4e8dce39fa8f 100644
> > --- a/fs/notify/fanotify/fanotify.c
> > +++ b/fs/notify/fanotify/fanotify.c
> > @@ -549,9 +549,13 @@ static struct fanotify_event *fanotify_alloc_path_event(const struct path *path,
> >  	return &pevent->fae;
> >  }
> >  
> > -static struct fanotify_event *fanotify_alloc_perm_event(const struct path *path,
> > +static struct fanotify_event *fanotify_alloc_perm_event(const void *data,
> > +							int data_type,
> >  							gfp_t gfp)
> >  {
> > +	const struct path *path = fsnotify_data_path(data, data_type);
> > +	const struct file_range *range =
> > +			    fsnotify_data_file_range(data, data_type);
> >  	struct fanotify_perm_event *pevent;
> >  
> >  	pevent = kmem_cache_alloc(fanotify_perm_event_cachep, gfp);
> > @@ -565,6 +569,8 @@ static struct fanotify_event *fanotify_alloc_perm_event(const struct path *path,
> >  	pevent->hdr.len = 0;
> >  	pevent->state = FAN_EVENT_INIT;
> >  	pevent->path = *path;
> > +	pevent->ppos = range ? range->ppos : NULL;
> > +	pevent->count = range ? range->count : 0;
> >  	path_get(path);
> >  
> >  	return &pevent->fae;
> > @@ -802,7 +808,7 @@ static struct fanotify_event *fanotify_alloc_event(
> >  	old_memcg = set_active_memcg(group->memcg);
> >  
> >  	if (fanotify_is_perm_event(mask)) {
> > -		event = fanotify_alloc_perm_event(path, gfp);
> > +		event = fanotify_alloc_perm_event(data, data_type, gfp);
> >  	} else if (fanotify_is_error_event(mask)) {
> >  		event = fanotify_alloc_error_event(group, fsid, data,
> >  						   data_type, &hash);
> > diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
> > index e5ab33cae6a7..93598b7d5952 100644
> > --- a/fs/notify/fanotify/fanotify.h
> > +++ b/fs/notify/fanotify/fanotify.h
> > @@ -425,6 +425,8 @@ FANOTIFY_PE(struct fanotify_event *event)
> >  struct fanotify_perm_event {
> >  	struct fanotify_event fae;
> >  	struct path path;
> > +	const loff_t *ppos;		/* optional file range info */
> > +	size_t count;
> >  	u32 response;			/* userspace answer to the event */
> >  	unsigned short state;		/* state of the event */
> >  	int fd;		/* fd we passed to userspace for this event */
> > diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
> > index a28daf136fea..4609d9b6b087 100644
> > --- a/include/linux/fsnotify.h
> > +++ b/include/linux/fsnotify.h
> > @@ -132,6 +132,21 @@ static inline int fsnotify_file(struct file *file, __u32 mask)
> >  }
> >  
> >  #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
> > +static inline int fsnotify_file_range(struct file *file, __u32 mask,
> > +				      const loff_t *ppos, size_t count)
> > +{
> > +	struct file_range range;
> > +
> > +	if (file->f_mode & FMODE_NONOTIFY)
> > +		return 0;
> > +
> > +	range.path = &file->f_path;
> > +	range.ppos = ppos;
> > +	range.count = count;
> > +	return fsnotify_parent(range.path->dentry, mask, &range,
> > +			       FSNOTIFY_EVENT_FILE_RANGE);
> > +}
> > +
> >  /*
> >   * fsnotify_file_area_perm - permission hook before access/modify of file range
> >   */
> > @@ -175,7 +190,7 @@ static inline int fsnotify_file_area_perm(struct file *file, int perm_mask,
> >  	else
> >  		return 0;
> >  
> > -	return fsnotify_file(file, fsnotify_mask);
> > +	return fsnotify_file_range(file, fsnotify_mask, ppos, count);
> >  }
> >  
> >  /*
> > diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
> > index 200a5e3b1cd4..276320846bfd 100644
> > --- a/include/linux/fsnotify_backend.h
> > +++ b/include/linux/fsnotify_backend.h
> > @@ -298,6 +298,7 @@ static inline void fsnotify_group_assert_locked(struct fsnotify_group *group)
> >  /* When calling fsnotify tell it if the data is a path or inode */
> >  enum fsnotify_data_type {
> >  	FSNOTIFY_EVENT_NONE,
> > +	FSNOTIFY_EVENT_FILE_RANGE,
> >  	FSNOTIFY_EVENT_PATH,
> >  	FSNOTIFY_EVENT_INODE,
> >  	FSNOTIFY_EVENT_DENTRY,
> > @@ -310,6 +311,17 @@ struct fs_error_report {
> >  	struct super_block *sb;
> >  };
> >  
> > +struct file_range {
> > +	const struct path *path;
> > +	const loff_t *ppos;
> > +	size_t count;
> > +};
> > +
> > +static inline const struct path *file_range_path(const struct file_range *range)
> > +{
> > +	return range->path;
> > +}
> > +
> >  static inline struct inode *fsnotify_data_inode(const void *data, int data_type)
> >  {
> >  	switch (data_type) {
> > @@ -319,6 +331,8 @@ static inline struct inode *fsnotify_data_inode(const void *data, int data_type)
> >  		return d_inode(data);
> >  	case FSNOTIFY_EVENT_PATH:
> >  		return d_inode(((const struct path *)data)->dentry);
> > +	case FSNOTIFY_EVENT_FILE_RANGE:
> > +		return d_inode(file_range_path(data)->dentry);
> >  	case FSNOTIFY_EVENT_ERROR:
> >  		return ((struct fs_error_report *)data)->inode;
> >  	default:
> > @@ -334,6 +348,8 @@ static inline struct dentry *fsnotify_data_dentry(const void *data, int data_typ
> >  		return (struct dentry *)data;
> >  	case FSNOTIFY_EVENT_PATH:
> >  		return ((const struct path *)data)->dentry;
> > +	case FSNOTIFY_EVENT_FILE_RANGE:
> > +		return file_range_path(data)->dentry;
> >  	default:
> >  		return NULL;
> >  	}
> > @@ -345,6 +361,8 @@ static inline const struct path *fsnotify_data_path(const void *data,
> >  	switch (data_type) {
> >  	case FSNOTIFY_EVENT_PATH:
> >  		return data;
> > +	case FSNOTIFY_EVENT_FILE_RANGE:
> > +		return file_range_path(data);
> >  	default:
> >  		return NULL;
> >  	}
> > @@ -360,6 +378,8 @@ static inline struct super_block *fsnotify_data_sb(const void *data,
> >  		return ((struct dentry *)data)->d_sb;
> >  	case FSNOTIFY_EVENT_PATH:
> >  		return ((const struct path *)data)->dentry->d_sb;
> > +	case FSNOTIFY_EVENT_FILE_RANGE:
> > +		return file_range_path(data)->dentry->d_sb;
> >  	case FSNOTIFY_EVENT_ERROR:
> >  		return ((struct fs_error_report *) data)->sb;
> >  	default:
> > @@ -379,6 +399,18 @@ static inline struct fs_error_report *fsnotify_data_error_report(
> >  	}
> >  }
> >  
> > +static inline const struct file_range *fsnotify_data_file_range(
> > +							const void *data,
> > +							int data_type)
> > +{
> > +	switch (data_type) {
> > +	case FSNOTIFY_EVENT_FILE_RANGE:
> > +		return (struct file_range *)data;
> > +	default:
> > +		return NULL;
> 
> Wouldn't you want something like
> 
> case FSNOTIFY_EVENT_NONE
> 	return NULL;
> default:
> 	WARN_ON_ONCE(data_type);
> 	return NULL;
> 
> to guard against garbage being passed to fsnotify_data_file_range()?

We don't do this in any of the other helpers, and this is used generically in
fanotify_alloc_perm_event(), which handles having no range properly.  Thanks,

Josef