fanotify_mark(2) System Calls Manual fanotify_mark(2)

fanotify_mark - add, remove, or modify an fanotify mark on a filesystem object

Standard C library (libc, -lc)

#include <sys/fanotify.h>
int fanotify_mark(int fanotify_fd, unsigned int flags,
                  uint64_t mask, int dirfd,
                  const char *_Nullable pathname);

For an overview of the fanotify API, see fanotify(7).

fanotify_mark() adds, removes, or modifies an fanotify mark on a filesystem object. The caller must have read permission on the filesystem object that is to be marked.

The fanotify_fd argument is a file descriptor returned by fanotify_init(2).

flags is a bit mask describing the modification to perform. It must include exactly one of the following values:

The events in mask will be added to the mark mask (or to the ignore mask). mask must be nonempty or the error EINVAL will occur.
The events in argument mask will be removed from the mark mask (or from the ignore mask). mask must be nonempty or the error EINVAL will occur.
Remove either all marks for filesystems, all marks for mounts, or all marks for directories and files from the fanotify group. If flags contains FAN_MARK_MOUNT, all marks for mounts are removed from the group. If flags contains FAN_MARK_FILESYSTEM, all marks for filesystems are removed from the group. Otherwise, all marks for directories and files are removed. No flag other than, and at most one of, the flags FAN_MARK_MOUNT or FAN_MARK_FILESYSTEM can be used in conjunction with FAN_MARK_FLUSH. mask is ignored.

If none of the values above is specified, or more than one is specified, the call fails with the error EINVAL.

In addition, zero or more of the following values may be ORed into flags:

If pathname is a symbolic link, mark the link itself, rather than the file to which it refers. (By default, fanotify_mark() dereferences pathname if it is a symbolic link.)
If the filesystem object to be marked is not a directory, the error ENOTDIR shall be raised.
Mark the mount specified by pathname. If pathname is not itself a mount point, the mount containing pathname will be marked. All directories, subdirectories, and the contained files of the mount will be monitored. The events which require that filesystem objects are identified by file handles, such as FAN_CREATE, FAN_ATTRIB, FAN_MOVE, and FAN_DELETE_SELF, cannot be provided as a mask when flags contains FAN_MARK_MOUNT. Attempting to do so will result in the error EINVAL being returned. Use of this flag requires the CAP_SYS_ADMIN capability.
Mark the filesystem specified by pathname. The filesystem containing pathname will be marked. All the contained files and directories of the filesystem from any mount point will be monitored. Use of this flag requires the CAP_SYS_ADMIN capability.
The events in mask shall be added to or removed from the ignore mask. Note that the flags FAN_ONDIR, and FAN_EVENT_ON_CHILD have no effect when provided with this flag. The effect of setting the flags FAN_ONDIR, and FAN_EVENT_ON_CHILD in the mark mask on the events that are set in the ignore mask is undefined and depends on the Linux kernel version. Specifically, prior to Linux 5.9, setting a mark mask on a file and a mark with ignore mask on its parent directory would not result in ignoring events on the file, regardless of the FAN_EVENT_ON_CHILD flag in the parent directory's mark mask. When the ignore mask is updated with the FAN_MARK_IGNORED_MASK flag on a mark that was previously updated with the FAN_MARK_IGNORE flag, the update fails with EEXIST error.
This flag has a similar effect as setting the FAN_MARK_IGNORED_MASK flag. The events in mask shall be added to or removed from the ignore mask. Unlike the FAN_MARK_IGNORED_MASK flag, this flag also has the effect that the FAN_ONDIR, and FAN_EVENT_ON_CHILD flags take effect on the ignore mask. Specifically, unless the FAN_ONDIR flag is set with FAN_MARK_IGNORE, events on directories will not be ignored. If the flag FAN_EVENT_ON_CHILD is set with FAN_MARK_IGNORE, events on children will be ignored. For example, a mark on a directory with combination of a mask with FAN_CREATE event and FAN_ONDIR flag and an ignore mask with FAN_CREATE event and without FAN_ONDIR flag, will result in getting only the events for creation of sub-directories. When using the FAN_MARK_IGNORE flag to add to an ignore mask of a mount, filesystem, or directory inode mark, the FAN_MARK_IGNORED_SURV_MODIFY flag must be specified. Failure to do so will results with EINVAL or EISDIR error.
The ignore mask shall survive modify events. If this flag is not set, the ignore mask is cleared when a modify event occurs on the marked object. Omitting this flag is typically used to suppress events (e.g., FAN_OPEN) for a specific file, until that specific file's content has been modified. It is far less useful to suppress events on an entire filesystem, or mount, or on all files inside a directory, until some file's content has been modified. For this reason, the FAN_MARK_IGNORE flag requires the FAN_MARK_IGNORED_SURV_MODIFY flag on a mount, filesystem, or directory inode mark. This flag cannot be removed from a mark once set. When the ignore mask is updated without this flag on a mark that was previously updated with the FAN_MARK_IGNORE and FAN_MARK_IGNORED_SURV_MODIFY flags, the update fails with EEXIST error.
This is a synonym for (FAN_MARK_IGNORE|FAN_MARK_IGNORED_SURV_MODIFY).
When an inode mark is created with this flag, the inode object will not be pinned to the inode cache, therefore, allowing the inode object to be evicted from the inode cache when the memory pressure on the system is high. The eviction of the inode object results in the evictable mark also being lost. When the mask of an evictable inode mark is updated without using the FAN_MARK_EVICATBLE flag, the marked inode is pinned to inode cache and the mark is no longer evictable. When the mask of a non-evictable inode mark is updated with the FAN_MARK_EVICTABLE flag, the inode mark remains non-evictable and the update fails with EEXIST error. Mounts and filesystems are not evictable objects, therefore, an attempt to create a mount mark or a filesystem mark with the FAN_MARK_EVICTABLE flag, will result in the error EINVAL. For example, inode marks can be used in combination with mount marks to reduce the amount of events from noninteresting paths. The event listener reads events, checks if the path reported in the event is of interest, and if it is not, the listener sets a mark with an ignore mask on the directory. Evictable inode marks allow using this method for a large number of directories without the concern of pinning all inodes and exhausting the system's memory.

mask defines which events shall be listened for (or which shall be ignored). It is a bit mask composed of the following values:

Create an event when a file or directory (but see BUGS) is accessed (read).
Create an event when a file is modified (write).
Create an event when a writable file is closed.
Create an event when a read-only file or directory is closed.
Create an event when a file or directory is opened.
Create an event when a file is opened with the intent to be executed. See NOTES for additional details.
Create an event when the metadata for a file or directory has changed. An fanotify group that identifies filesystem objects by file handles is required.
Create an event when a file or directory has been created in a marked parent directory. An fanotify group that identifies filesystem objects by file handles is required.
Create an event when a file or directory has been deleted in a marked parent directory. An fanotify group that identifies filesystem objects by file handles is required.
Create an event when a marked file or directory itself is deleted. An fanotify group that identifies filesystem objects by file handles is required.
Create an event when a filesystem error leading to inconsistent filesystem metadata is detected. An additional information record of type FAN_EVENT_INFO_TYPE_ERROR is returned for each event in the read buffer. An fanotify group that identifies filesystem objects by file handles is required.
Events of such type are dependent on support from the underlying filesystem. At the time of writing, only the ext4 filesystem reports FAN_FS_ERROR events.
See fanotify(7) for additional details.
Create an event when a file or directory has been moved from a marked parent directory. An fanotify group that identifies filesystem objects by file handles is required.
Create an event when a file or directory has been moved to a marked parent directory. An fanotify group that identifies filesystem objects by file handles is required.
This event contains the same information provided by events FAN_MOVED_FROM and FAN_MOVED_TO, however is represented by a single event with up to two information records. An fanotify group that identifies filesystem objects by file handles is required. If the filesystem object to be marked is not a directory, the error ENOTDIR shall be raised.
Create an event when a marked file or directory itself has been moved. An fanotify group that identifies filesystem objects by file handles is required.
Create an event when a permission to open a file or directory is requested. An fanotify file descriptor created with FAN_CLASS_PRE_CONTENT or FAN_CLASS_CONTENT is required.
Create an event when a permission to open a file for execution is requested. An fanotify file descriptor created with FAN_CLASS_PRE_CONTENT or FAN_CLASS_CONTENT is required. See NOTES for additional details.
Create an event when a permission to read a file or directory is requested. An fanotify file descriptor created with FAN_CLASS_PRE_CONTENT or FAN_CLASS_CONTENT is required.
Create events for directories—for example, when opendir(3), readdir(3) (but see BUGS), and closedir(3) are called. Without this flag, events are created only for files. In the context of directory entry events, such as FAN_CREATE, FAN_DELETE, FAN_MOVED_FROM, and FAN_MOVED_TO, specifying the flag FAN_ONDIR is required in order to create events when subdirectory entries are modified (i.e., mkdir(2)/ rmdir(2)).
Events for the immediate children of marked directories shall be created. The flag has no effect when marking mounts and filesystems. Note that events are not generated for children of the subdirectories of marked directories. More specifically, the directory entry modification events FAN_CREATE, FAN_DELETE, FAN_MOVED_FROM, and FAN_MOVED_TO are not generated for any entry modifications performed inside subdirectories of marked directories. Note that the events FAN_DELETE_SELF and FAN_MOVE_SELF are not generated for children of marked directories. To monitor complete directory trees it is necessary to mark the relevant mount or filesystem.

The following composed values are defined:

A file is closed (FAN_CLOSE_WRITE|FAN_CLOSE_NOWRITE).
A file or directory has been moved (FAN_MOVED_FROM|FAN_MOVED_TO).

The filesystem object to be marked is determined by the file descriptor dirfd and the pathname specified in pathname:

•
If pathname is NULL, dirfd defines the filesystem object to be marked.
•
If pathname is NULL, and dirfd takes the special value AT_FDCWD, the current working directory is to be marked.
•
If pathname is absolute, it defines the filesystem object to be marked, and dirfd is ignored.
•
If pathname is relative, and dirfd does not have the value AT_FDCWD, then the filesystem object to be marked is determined by interpreting pathname relative the directory referred to by dirfd.
•
If pathname is relative, and dirfd has the value AT_FDCWD, then the filesystem object to be marked is determined by interpreting pathname relative to the current working directory. (See openat(2) for an explanation of why the dirfd argument is useful.)

On success, fanotify_mark() returns 0. On error, -1 is returned, and errno is set to indicate the error.

An invalid file descriptor was passed in fanotify_fd.
pathname is relative but dirfd is neither AT_FDCWD nor a valid file descriptor.
The filesystem object indicated by dirfd and pathname has a mark that was updated without the FAN_MARK_EVICTABLE flag, and the user attempted to update the mark with FAN_MARK_EVICTABLE flag.
The filesystem object indicated by dirfd and pathname has a mark that was updated with the FAN_MARK_IGNORE flag, and the user attempted to update the mark with FAN_MARK_IGNORED_MASK flag.
The filesystem object indicated by dirfd and pathname has a mark that was updated with the FAN_MARK_IGNORE and FAN_MARK_IGNORED_SURV_MODIFY flags, and the user attempted to update the mark only with FAN_MARK_IGNORE flag.
An invalid value was passed in flags or mask, or fanotify_fd was not an fanotify file descriptor.
The fanotify file descriptor was opened with FAN_CLASS_NOTIF or the fanotify group identifies filesystem objects by file handles and mask contains a flag for permission events (FAN_OPEN_PERM or FAN_ACCESS_PERM).
The group was initialized without FAN_REPORT_FID but one or more event types specified in the mask require it.
flags contains FAN_MARK_IGNORE, and either FAN_MARK_MOUNT or FAN_MARK_FILESYSTEM, but does not contain FAN_MARK_IGNORED_SURV_MODIFY.
flags contains FAN_MARK_IGNORE, but does not contain FAN_MARK_IGNORED_SURV_MODIFY, and dirfd and pathname specify a directory.
The filesystem object indicated by dirfd and pathname is not associated with a filesystem that supports fsid (e.g., fuse(4)). tmpfs(5) did not support fsid prior to Linux 5.13. This error can be returned only with an fanotify group that identifies filesystem objects by file handles.
The filesystem object indicated by dirfd and pathname does not exist. This error also occurs when trying to remove a mark from an object which is not marked.
The necessary memory could not be allocated.
The number of marks for this user exceeds the limit and the FAN_UNLIMITED_MARKS flag was not specified when the fanotify file descriptor was created with fanotify_init(2). See fanotify(7) for details about this limit.
This kernel does not implement fanotify_mark(). The fanotify API is available only if the kernel was configured with CONFIG_FANOTIFY.
flags contains FAN_MARK_ONLYDIR, and dirfd and pathname do not specify a directory.
mask contains FAN_RENAME, and dirfd and pathname do not specify a directory.
flags contains FAN_MARK_IGNORE, or the fanotify group was initialized with flag FAN_REPORT_TARGET_FID, and mask contains directory entry modification events (e.g., FAN_CREATE, FAN_DELETE), or directory event flags (e.g., FAN_ONDIR, FAN_EVENT_ON_CHILD), and dirfd and pathname do not specify a directory.
The object indicated by pathname is associated with a filesystem that does not support the encoding of file handles. This error can be returned only with an fanotify group that identifies filesystem objects by file handles. Calling name_to_handle_at(2) with the flag AT_HANDLE_FID (since Linux 6.5) can be used as a test to check if a filesystem supports reporting events with file handles.
The operation is not permitted because the caller lacks a required capability.
The filesystem object indicated by pathname resides within a filesystem subvolume (e.g., btrfs(5)) which uses a different fsid than its root superblock. This error can be returned only with an fanotify group that identifies filesystem objects by file handles.

Linux.

Linux 2.6.37.

When using either FAN_OPEN_EXEC or FAN_OPEN_EXEC_PERM within the mask, events of these types will be returned only when the direct execution of a program occurs. More specifically, this means that events of these types will be generated for files that are opened using execve(2), execveat(2), or uselib(2). Events of these types will not be raised in the situation where an interpreter is passed (or reads) a file for interpretation.

Additionally, if a mark has also been placed on the Linux dynamic linker, a user should also expect to receive an event for it when an ELF object has been successfully opened using execve(2) or execveat(2).

For example, if the following ELF binary were to be invoked and a FAN_OPEN_EXEC mark has been placed on /:


$ /bin/echo foo

The listening application in this case would receive FAN_OPEN_EXEC events for both the ELF binary and interpreter, respectively:


/bin/echo
/lib64/ld-linux-x86-64.so.2

The following bugs were present in before Linux 3.16:

•
If flags contains FAN_MARK_FLUSH, dirfd, and pathname must specify a valid filesystem object, even though this object is not used.
•
readdir(2) does not generate a FAN_ACCESS event.
•
If fanotify_mark() is called with FAN_MARK_FLUSH, flags is not checked for invalid values.

fanotify_init(2), fanotify(7)

2023-10-31 Linux man-pages 6.7