Commit 4f8afa33 authored by Amir Goldstein's avatar Amir Goldstein Committed by Jan Kara
Browse files

fanotify: introduce FAN_PRE_ACCESS permission event 



Similar to FAN_ACCESS_PERM permission event, but it is only allowed with
class FAN_CLASS_PRE_CONTENT and only allowed on regular files and dirs.

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: default avatarAmir Goldstein <amir73il@gmail.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Link: https://patch.msgid.link/b80986f8d5b860acea2c9a73c0acd93587be5fe4.1731684329.git.josef@toxicpanda.com
parent 4acf3bc7

fs/notify/fanotify/fanotify.c

+2 −1
Original line number Diff line number Diff line
@@ -916,8 +916,9 @@ 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);

fs/notify/fanotify/fanotify_user.c

+30 −5
Original line number Diff line number Diff line
@@ -1287,7 +1287,7 @@ static int fanotify_group_init_error_pool(struct fsnotify_group *group) 
}



static int fanotify_may_update_existing_mark(struct fsnotify_mark *fsn_mark,

					      unsigned int fan_flags)

					     __u32 mask, unsigned int fan_flags)

{

	/*

	 * Non evictable mark cannot be downgraded to evictable mark.
@@ -1314,6 +1314,11 @@ static int fanotify_may_update_existing_mark(struct fsnotify_mark *fsn_mark, 
	    fsn_mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY)

		return -EEXIST;



	/* For now pre-content events are not generated for directories */

	mask |= fsn_mark->mask;

	if (mask & FANOTIFY_PRE_CONTENT_EVENTS && mask & FAN_ONDIR)

		return -EEXIST;



	return 0;

}
@@ -1340,7 +1345,7 @@ static int fanotify_add_mark(struct fsnotify_group *group, 
	/*

	 * Check if requested mark flags conflict with an existing mark flags.

	 */

	ret = fanotify_may_update_existing_mark(fsn_mark, fan_flags);

	ret = fanotify_may_update_existing_mark(fsn_mark, mask, fan_flags);

	if (ret)

		goto out;
@@ -1640,11 +1645,23 @@ 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) ||

				 (flags & FAN_MARK_IGNORE);



	/*

	 * Filesystems need to opt-into pre-content evnets (a.k.a HSM)

	 * and they are only supported on regular files and directories.

	 */

	if (mask & FANOTIFY_PRE_CONTENT_EVENTS) {

		if (!(path->mnt->mnt_sb->s_iflags & SB_I_ALLOW_HSM))

			return -EOPNOTSUPP;

		if (!is_dir && !d_is_reg(path->dentry))

			return -EINVAL;

	}



	/*

	 * Some filesystems such as 'proc' acquire unusual locks when opening

	 * files. For them fanotify permission events have high chances of
@@ -1677,7 +1694,7 @@ 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;



	return 0;
@@ -1778,10 +1795,14 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask, 
		return -EPERM;



	/*

	 * 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.

	 */

	if (mask & FANOTIFY_PERM_EVENTS &&

	    group->priority < FSNOTIFY_PRIO_CONTENT)

	    group->priority == FSNOTIFY_PRIO_NORMAL)

		return -EINVAL;

	else if (mask & FANOTIFY_PRE_CONTENT_EVENTS &&

		 group->priority == FSNOTIFY_PRIO_CONTENT)

		return -EINVAL;



	if (mask & FAN_FS_ERROR &&
@@ -1816,6 +1837,10 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask, 
	if (mask & FAN_RENAME && !(fid_mode & FAN_REPORT_NAME))

		return -EINVAL;



	/* Pre-content events are not currently generated for directories. */

	if (mask & FANOTIFY_PRE_CONTENT_EVENTS && mask & FAN_ONDIR)

		return -EINVAL;



	if (mark_cmd == FAN_MARK_FLUSH) {

		if (mark_type == FAN_MARK_MOUNT)

			fsnotify_clear_vfsmount_marks_by_group(group);

include/linux/fanotify.h

+10 −4
Original line number Diff line number Diff line
@@ -89,6 +89,16 @@ 
#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)
@@ -104,10 +114,6 @@ 
				 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)

include/uapi/linux/fanotify.h

+2 −0
Original line number Diff line number Diff line
@@ -27,6 +27,8 @@ 
#define FAN_OPEN_EXEC_PERM	0x00040000	/* File open/exec in perm check */

/* #define FAN_DIR_MODIFY	0x00080000 */	/* Deprecated (reserved) */



#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 */