fanotify_mark.2

.\" Copyright (C) 2013,  Heinrich Schuchardt <xypron.glpk@gmx.de>
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.TH FANOTIFY_MARK 2 2021-08-27 "Linux" "Linux Programmer's Manual"
.SH NAME
fanotify_mark \- add, remove, or modify an fanotify mark on a filesystem
object
.SH SYNOPSIS
.nf
.B #include <sys/fanotify.h>
.PP
.BI "int fanotify_mark(int " fanotify_fd ", unsigned int " flags ,
.BI "                  uint64_t " mask ", int " dirfd \
", const char *" pathname );
.fi
.SH DESCRIPTION
For an overview of the fanotify API, see
.BR fanotify (7).
.PP
.BR 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.
.PP
The
.I fanotify_fd
argument is a file descriptor returned by
.BR fanotify_init (2).
.PP
.I flags
is a bit mask describing the modification to perform.
It must include exactly one of the following values:
.TP
.B FAN_MARK_ADD
The events in
.I mask
will be added to the mark mask (or to the ignore mask).
.I mask
must be nonempty or the error
.B EINVAL
will occur.
.TP
.B FAN_MARK_REMOVE
The events in argument
.I mask
will be removed from the mark mask (or from the ignore mask).
.I mask
must be nonempty or the error
.B EINVAL
will occur.
.TP
.B FAN_MARK_FLUSH
Remove either all marks for filesystems, all marks for mounts, or all
marks for directories and files from the fanotify group.
If
.I flags
contains
.BR FAN_MARK_MOUNT ,
all marks for mounts are removed from the group.
If
.I flags
contains
.BR 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
.B FAN_MARK_MOUNT
or
.B FAN_MARK_FILESYSTEM
can be used in conjunction with
.BR FAN_MARK_FLUSH .
.I mask
is ignored.
.PP
If none of the values above is specified, or more than one is specified,
the call fails with the error
.BR EINVAL .
.PP
In addition,
zero or more of the following values may be ORed into
.IR flags :
.TP
.B FAN_MARK_DONT_FOLLOW
If
.I pathname
is a symbolic link, mark the link itself, rather than the file to which it
refers.
(By default,
.BR fanotify_mark ()
dereferences
.I pathname
if it is a symbolic link.)
.TP
.B FAN_MARK_ONLYDIR
If the filesystem object to be marked is not a directory, the error
.B ENOTDIR
shall be raised.
.TP
.B FAN_MARK_MOUNT
Mark the mount specified by
.IR pathname .
If
.I pathname
is not itself a mount point, the mount containing
.I 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
.BR FAN_CREATE ,
.BR FAN_ATTRIB ,
.BR FAN_MOVE ,
and
.BR FAN_DELETE_SELF ,
cannot be provided as a
.IR mask
when
.I flags
contains
.BR FAN_MARK_MOUNT .
Attempting to do so will result in the error
.B EINVAL
being returned.
.TP
.BR FAN_MARK_FILESYSTEM " (since Linux 4.20)"
.\" commit d54f4fba889b205e9cd8239182ca5d27d0ac3bc2
Mark the filesystem specified by
.IR pathname .
The filesystem containing
.I pathname
will be marked.
All the contained files and directories of the filesystem from any mount
point will be monitored.
.TP
.B FAN_MARK_IGNORED_MASK
The events in
.I mask
shall be added to or removed from the ignore mask.
.TP
.B FAN_MARK_IGNORED_SURV_MODIFY
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.
.PP
.I mask
defines which events shall be listened for (or which shall be ignored).
It is a bit mask composed of the following values:
.TP
.B FAN_ACCESS
Create an event when a file or directory (but see BUGS) is accessed (read).
.TP
.B FAN_MODIFY
Create an event when a file is modified (write).
.TP
.B FAN_CLOSE_WRITE
Create an event when a writable file is closed.
.TP
.B FAN_CLOSE_NOWRITE
Create an event when a read-only file or directory is closed.
.TP
.B FAN_OPEN
Create an event when a file or directory is opened.
.TP
.BR FAN_OPEN_EXEC " (since Linux 5.0)"
.\" commit 9b076f1c0f4869b838a1b7aa0edb5664d47ec8aa
Create an event when a file is opened with the intent to be executed.
See NOTES for additional details.
.TP
.BR FAN_ATTRIB " (since Linux 5.1)"
.\" commit 235328d1fa4251c6dcb32351219bb553a58838d2
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.
.TP
.BR FAN_CREATE " (since Linux 5.1)"
.\" commit 235328d1fa4251c6dcb32351219bb553a58838d2
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.
.TP
.BR FAN_DELETE " (since Linux 5.1)"
.\" commit 235328d1fa4251c6dcb32351219bb553a58838d2
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.
.TP
.BR FAN_DELETE_SELF " (since Linux 5.1)"
.\" commit 235328d1fa4251c6dcb32351219bb553a58838d2
Create an event when a marked file or directory itself is deleted.
An fanotify group that identifies filesystem objects by file handles
is required.
.TP
.BR FAN_MOVED_FROM " (since Linux 5.1)"
.\" commit 235328d1fa4251c6dcb32351219bb553a58838d2
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.
.TP
.BR FAN_MOVED_TO " (since Linux 5.1)"
.\" commit 235328d1fa4251c6dcb32351219bb553a58838d2
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.
.TP
.BR FAN_MOVE_SELF " (since Linux 5.1)"
.\" commit 235328d1fa4251c6dcb32351219bb553a58838d2
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.
.TP
.B FAN_OPEN_PERM
Create an event when a permission to open a file or directory is requested.
An fanotify file descriptor created with
.B FAN_CLASS_PRE_CONTENT
or
.B FAN_CLASS_CONTENT
is required.
.TP
.BR FAN_OPEN_EXEC_PERM " (since Linux 5.0)"
.\" commit 66917a3130f218dcef9eeab4fd11a71cd00cd7c9
Create an event when a permission to open a file for execution is
requested.
An fanotify file descriptor created with
.B FAN_CLASS_PRE_CONTENT
or
.B FAN_CLASS_CONTENT
is required.
See NOTES for additional details.
.TP
.B FAN_ACCESS_PERM
Create an event when a permission to read a file or directory is requested.
An fanotify file descriptor created with
.B FAN_CLASS_PRE_CONTENT
or
.B FAN_CLASS_CONTENT
is required.
.TP
.B FAN_ONDIR
Create events for directories\(emfor example, when
.BR opendir (3),
.BR readdir (3)
(but see BUGS), and
.BR closedir (3)
are called.
Without this flag, events are created only for files.
In the context of directory entry events, such as
.BR FAN_CREATE ,
.BR FAN_DELETE ,
.BR FAN_MOVED_FROM ,
and
.BR FAN_MOVED_TO ,
specifying the flag
.BR FAN_ONDIR
is required in order to create events when subdirectory entries are
modified (i.e.,
.BR mkdir (2)/
.BR rmdir (2)).
.TP
.B FAN_EVENT_ON_CHILD
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
.BR FAN_CREATE ,
.BR FAN_DELETE ,
.BR FAN_MOVED_FROM ,
and
.BR FAN_MOVED_TO
are not generated for any entry modifications performed inside subdirectories
of marked directories.
Note that the events
.BR FAN_DELETE_SELF
and
.BR 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.
.PP
The following composed values are defined:
.TP
.B FAN_CLOSE
A file is closed
.RB ( FAN_CLOSE_WRITE | FAN_CLOSE_NOWRITE ).
.TP
.B FAN_MOVE
A file or directory has been moved
.RB ( FAN_MOVED_FROM | FAN_MOVED_TO ).
.PP
The filesystem object to be marked is determined by the file descriptor
.I dirfd
and the pathname specified in
.IR pathname :
.IP * 3
If
.I pathname
is NULL,
.I dirfd
defines the filesystem object to be marked.
.IP *
If
.I pathname
is NULL, and
.I dirfd
takes the special value
.BR AT_FDCWD ,
the current working directory is to be marked.
.IP *
If
.I pathname
is absolute, it defines the filesystem object to be marked, and
.I dirfd
is ignored.
.IP *
If
.I pathname
is relative, and
.I dirfd
does not have the value
.BR AT_FDCWD ,
then the filesystem object to be marked is determined by interpreting
.I pathname
relative the directory referred to by
.IR dirfd .
.IP *
If
.I pathname
is relative, and
.I dirfd
has the value
.BR AT_FDCWD ,
then the filesystem object to be marked is determined by interpreting
.I pathname
relative to the current working directory.
(See
.BR openat (2)
for an explanation of why the
.I dirfd
argument is useful.)
.SH RETURN VALUE
On success,
.BR fanotify_mark ()
returns 0.
On error, \-1 is returned, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EBADF
An invalid file descriptor was passed in
.IR fanotify_fd .
.TP
.B EBADF
.I pathname
is relative but
.I dirfd
is neither
.B AT_FDCWD
nor a valid file descriptor.
.TP
.B EINVAL
An invalid value was passed in
.IR flags
or
.IR mask ,
or
.I fanotify_fd
was not an fanotify file descriptor.
.TP
.B EINVAL
The fanotify file descriptor was opened with
.B FAN_CLASS_NOTIF
or the fanotify group identifies filesystem objects by file handles
and mask contains a flag for permission events
.RB ( FAN_OPEN_PERM
or
.BR FAN_ACCESS_PERM ).
.TP
.B ENODEV
The filesystem object indicated by
.I pathname
is not associated with a filesystem that supports
.I fsid
(e.g.,
.BR tmpfs (5)).
This error can be returned only with an fanotify group that identifies
filesystem objects by file handles.
.TP
.B ENOENT
The filesystem object indicated by
.IR dirfd
and
.IR pathname
does not exist.
This error also occurs when trying to remove a mark from an object
which is not marked.
.TP
.B ENOMEM
The necessary memory could not be allocated.
.TP
.B ENOSPC
The number of marks exceeds the limit of 8192 and the
.B FAN_UNLIMITED_MARKS
flag was not specified when the fanotify file descriptor was created with
.BR fanotify_init (2).
.TP
.B ENOSYS
This kernel does not implement
.BR fanotify_mark ().
The fanotify API is available only if the kernel was configured with
.BR CONFIG_FANOTIFY .
.TP
.B ENOTDIR
.I flags
contains
.BR FAN_MARK_ONLYDIR ,
and
.I dirfd
and
.I pathname
do not specify a directory.
.TP
.B EOPNOTSUPP
The object indicated by
.I 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.
.TP
.B EXDEV
The filesystem object indicated by
.I pathname
resides within a filesystem subvolume (e.g.,
.BR btrfs (5))
which uses a different
.I fsid
than its root superblock.
This error can be returned only with an fanotify group that identifies
filesystem objects by file handles.
.SH VERSIONS
.BR fanotify_mark ()
was introduced in version 2.6.36 of the Linux kernel and enabled in version
2.6.37.
.SH CONFORMING TO
This system call is Linux-specific.
.SH NOTES
.SS FAN_OPEN_EXEC and FAN_OPEN_EXEC_PERM
When using either
.B FAN_OPEN_EXEC
or
.B FAN_OPEN_EXEC_PERM
within the
.IR 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
.BR execve (2),
.BR execveat (2),
or
.BR uselib (2).
Events of these types will not be raised in the situation where an
interpreter is passed (or reads) a file for interpretation.
.PP
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
.BR execve (2)
or
.BR execveat (2).
.PP
For example, if the following ELF binary were to be invoked and a
.BR FAN_OPEN_EXEC
mark has been placed on /:
.PP
.in +4n
.EX
$ /bin/echo foo
.EE
.in
.PP
The listening application in this case would receive
.BR FAN_OPEN_EXEC
events for both the ELF binary and interpreter, respectively:
.PP
.in +4n
.EX
/bin/echo
/lib64/ld\-linux\-x86\-64.so.2
.EE
.in
.SH BUGS
The following bugs were present in Linux kernels before version 3.16:
.IP * 3
.\" Fixed by commit 0a8dd2db579f7a0ac7033d6b857c3d5dbaa77563
If
.I flags
contains
.BR FAN_MARK_FLUSH ,
.IR dirfd ,
and
.I pathname
must specify a valid filesystem object, even though this object is not used.
.IP *
.\" Fixed by commit d4c7cf6cffb1bc711a833b5e304ba5bcfe76398b
.BR readdir (2)
does not generate a
.B FAN_ACCESS
event.
.IP *
.\" Fixed by commit cc299a98eb13a9853675a9cbb90b30b4011e1406
If
.BR fanotify_mark ()
is called with
.BR FAN_MARK_FLUSH ,
.I flags
is not checked for invalid values.
.SH SEE ALSO
.BR fanotify_init (2),
.BR fanotify (7)