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

Christian Brauner
2024-08-09T12:00:34Z

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()?