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FANOTIFY_MARK(2) Linux Programmer's Manual FANOTIFY_MARK(2)

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

#include <sys/fanotify.h>
int fanotify_mark(int fanotify_fd, unsigned int flags,
                  uint64_t mask, int dirfd, const char *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 point specified by pathname. If pathname is not itself a mount point, the mount point containing pathname will be marked. All directories, subdirectories, and the contained files of the mount point 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.
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.
The events in mask shall be added to or removed from the ignore mask.
The ignore mask shall survive modify events. If this flag is not set, the ignore mask is cleared when a modify event occurs for the ignored file or directory.

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 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.
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 the current working directory.

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.
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 filesystem object indicated by pathname is not associated with a filesystem that supports fsid (e.g., tmpfs(5)). 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 exceeds the limit of 8192 and the FAN_UNLIMITED_MARKS flag was not specified when the fanotify file descriptor was created with fanotify_init(2).
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.
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.
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.

fanotify_mark() was introduced in version 2.6.36 of the Linux kernel and enabled in version 2.6.37.

This system call is Linux-specific.

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 Linux kernels before version 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)

This page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

2020-11-01 Linux