Re: [PATCH 04/10] fanotify: introduce FAN_PRE_ACCESS permission event

[Jan Kara <jack@suse.cz>]

On Thu 25-07-24 14:19:41, Josef Bacik wrote:
> From: Amir Goldstein <amir73il@gmail.com>
> 
> Similar to FAN_ACCESS_PERM permission event, but it is only allowed with
> class FAN_CLASS_PRE_CONTENT and only allowed on regular files are dirs.
								^^ and

> Unlike FAN_ACCESS_PERM, it is safe to write to the file being accessed
> in the context of the event handler.
> 
> This pre-content event is meant to be used by hierarchical storage
> managers that want to fill the content of files on first read access.
> 
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>

Otherwise the patch looks good.

								Honza

> ---
>  fs/notify/fanotify/fanotify.c      |  3 ++-
>  fs/notify/fanotify/fanotify_user.c | 17 ++++++++++++++---
>  include/linux/fanotify.h           | 14 ++++++++++----
>  include/uapi/linux/fanotify.h      |  2 ++
>  4 files changed, 28 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> index 224bccaab4cc..7dac8e4486df 100644
> --- a/fs/notify/fanotify/fanotify.c
> +++ b/fs/notify/fanotify/fanotify.c
> @@ -910,8 +910,9 @@ static int fanotify_handle_event(struct fsnotify_group *group, u32 mask,
>  	BUILD_BUG_ON(FAN_OPEN_EXEC_PERM != FS_OPEN_EXEC_PERM);
>  	BUILD_BUG_ON(FAN_FS_ERROR != FS_ERROR);
>  	BUILD_BUG_ON(FAN_RENAME != FS_RENAME);
> +	BUILD_BUG_ON(FAN_PRE_ACCESS != FS_PRE_ACCESS);
>  
> -	BUILD_BUG_ON(HWEIGHT32(ALL_FANOTIFY_EVENT_BITS) != 21);
> +	BUILD_BUG_ON(HWEIGHT32(ALL_FANOTIFY_EVENT_BITS) != 22);
>  
>  	mask = fanotify_group_event_mask(group, iter_info, &match_mask,
>  					 mask, data, data_type, dir);
> diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> index 2e2fba8a9d20..c294849e474f 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -1628,6 +1628,7 @@ static int fanotify_events_supported(struct fsnotify_group *group,
>  				     unsigned int flags)
>  {
>  	unsigned int mark_type = flags & FANOTIFY_MARK_TYPE_BITS;
> +	bool is_dir = d_is_dir(path->dentry);
>  	/* Strict validation of events in non-dir inode mask with v5.17+ APIs */
>  	bool strict_dir_events = FAN_GROUP_FLAG(group, FAN_REPORT_TARGET_FID) ||
>  				 (mask & FAN_RENAME) ||
> @@ -1665,9 +1666,15 @@ static int fanotify_events_supported(struct fsnotify_group *group,
>  	 * but because we always allowed it, error only when using new APIs.
>  	 */
>  	if (strict_dir_events && mark_type == FAN_MARK_INODE &&
> -	    !d_is_dir(path->dentry) && (mask & FANOTIFY_DIRONLY_EVENT_BITS))
> +	    !is_dir && (mask & FANOTIFY_DIRONLY_EVENT_BITS))
>  		return -ENOTDIR;
>  
> +	/* Pre-content events are only supported on regular files and dirs */
> +	if (mask & FANOTIFY_PRE_CONTENT_EVENTS) {
> +		if (!is_dir && !d_is_reg(path->dentry))
> +			return -EINVAL;
> +	}
> +
>  	return 0;
>  }
>  
> @@ -1769,11 +1776,15 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
>  		goto fput_and_out;
>  
>  	/*
> -	 * Permission events require minimum priority FAN_CLASS_CONTENT.
> +	 * Permission events are not allowed for FAN_CLASS_NOTIF.
> +	 * Pre-content permission events are not allowed for FAN_CLASS_CONTENT.
>  	 */
>  	ret = -EINVAL;
>  	if (mask & FANOTIFY_PERM_EVENTS &&
> -	    group->priority < FSNOTIFY_PRIO_CONTENT)
> +	    group->priority == FSNOTIFY_PRIO_NORMAL)
> +		goto fput_and_out;
> +	else if (mask & FANOTIFY_PRE_CONTENT_EVENTS &&
> +		 group->priority == FSNOTIFY_PRIO_CONTENT)
>  		goto fput_and_out;
>  
>  	if (mask & FAN_FS_ERROR &&
> diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h
> index 4f1c4f603118..5c811baf44d2 100644
> --- a/include/linux/fanotify.h
> +++ b/include/linux/fanotify.h
> @@ -88,6 +88,16 @@
>  #define FANOTIFY_DIRENT_EVENTS	(FAN_MOVE | FAN_CREATE | FAN_DELETE | \
>  				 FAN_RENAME)
>  
> +/* Content events can be used to inspect file content */
> +#define FANOTIFY_CONTENT_PERM_EVENTS (FAN_OPEN_PERM | FAN_OPEN_EXEC_PERM | \
> +				      FAN_ACCESS_PERM)
> +/* Pre-content events can be used to fill file content */
> +#define FANOTIFY_PRE_CONTENT_EVENTS  (FAN_PRE_ACCESS)
> +
> +/* Events that require a permission response from user */
> +#define FANOTIFY_PERM_EVENTS	(FANOTIFY_CONTENT_PERM_EVENTS | \
> +				 FANOTIFY_PRE_CONTENT_EVENTS)
> +
>  /* Events that can be reported with event->fd */
>  #define FANOTIFY_FD_EVENTS (FANOTIFY_PATH_EVENTS | FANOTIFY_PERM_EVENTS)
>  
> @@ -103,10 +113,6 @@
>  				 FANOTIFY_INODE_EVENTS | \
>  				 FANOTIFY_ERROR_EVENTS)
>  
> -/* Events that require a permission response from user */
> -#define FANOTIFY_PERM_EVENTS	(FAN_OPEN_PERM | FAN_ACCESS_PERM | \
> -				 FAN_OPEN_EXEC_PERM)
> -
>  /* Extra flags that may be reported with event or control handling of events */
>  #define FANOTIFY_EVENT_FLAGS	(FAN_EVENT_ON_CHILD | FAN_ONDIR)
>  
> diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h
> index a37de58ca571..3ae43867d318 100644
> --- a/include/uapi/linux/fanotify.h
> +++ b/include/uapi/linux/fanotify.h
> @@ -26,6 +26,8 @@
>  #define FAN_ACCESS_PERM		0x00020000	/* File accessed in perm check */
>  #define FAN_OPEN_EXEC_PERM	0x00040000	/* File open/exec in perm check */
>  
> +#define FAN_PRE_ACCESS		0x00100000	/* Pre-content access hook */
> +
>  #define FAN_EVENT_ON_CHILD	0x08000000	/* Interested in child events */
>  
>  #define FAN_RENAME		0x10000000	/* File was renamed */
> -- 
> 2.43.0
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR