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

[Christian Brauner <brauner@kernel.org>]

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()?