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diff --git a/man2/mount_setattr.2 b/man2/mount_setattr.2 deleted file mode 100644 index 3b70dcd97..000000000 --- a/man2/mount_setattr.2 +++ /dev/null @@ -1,1055 +0,0 @@ -.\" Copyright (c) 2021 by Christian Brauner <christian.brauner@ubuntu.com> -.\" -.\" SPDX-License-Identifier: Linux-man-pages-copyleft -.\" -.TH mount_setattr 2 (date) "Linux man-pages (unreleased)" -.SH NAME -mount_setattr \- change properties of a mount or mount tree -.SH LIBRARY -Standard C library -.RI ( libc ", " \-lc ) -.SH SYNOPSIS -.nf -.BR "#include <linux/fcntl.h>" " /* Definition of " AT_* " constants */" -.BR "#include <linux/mount.h>" " /* Definition of " MOUNT_ATTR_* " constants */" -.BR "#include <sys/syscall.h>" " /* Definition of " SYS_* " constants */" -.B #include <unistd.h> -.P -.BI "int syscall(SYS_mount_setattr, int " dirfd ", const char *" pathname , -.BI " unsigned int " flags ", struct mount_attr *" attr \ -", size_t " size ); -.fi -.P -.IR Note : -glibc provides no wrapper for -.BR mount_setattr (), -necessitating the use of -.BR syscall (2). -.SH DESCRIPTION -The -.BR mount_setattr () -system call changes the mount properties of a mount or an entire mount tree. -If -.I pathname -is a relative pathname, -then it is interpreted relative to -the directory referred to by the file descriptor -.IR dirfd . -If -.I dirfd -is the special value -.BR AT_FDCWD , -then -.I pathname -is interpreted relative to -the current working directory of the calling process. -If -.I pathname -is the empty string and -.B AT_EMPTY_PATH -is specified in -.IR flags , -then the mount properties of the mount identified by -.I dirfd -are changed. -(See -.BR openat (2) -for an explanation of why the -.I dirfd -argument is useful.) -.P -The -.BR mount_setattr () -system call uses an extensible structure -.RI ( "struct mount_attr" ) -to allow for future extensions. -Any non-flag extensions to -.BR mount_setattr () -will be implemented as new fields appended to the this structure, -with a zero value in a new field resulting in the kernel behaving -as though that extension field was not present. -Therefore, -the caller -.I must -zero-fill this structure on initialization. -See the "Extensibility" subsection under -.B NOTES -for more details. -.P -The -.I size -argument should usually be specified as -.IR "sizeof(struct mount_attr)" . -However, if the caller is using a kernel that supports an extended -.IR "struct mount_attr" , -but the caller does not intend to make use of these features, -it is possible to pass the size of an earlier -version of the structure together with the extended structure. -This allows the kernel to not copy later parts of the structure -that aren't used anyway. -With each extension that changes the size of -.IR "struct mount_attr" , -the kernel will expose a definition of the form -.BI MOUNT_ATTR_SIZE_VER number\c -\&. -For example, the macro for the size of the initial version of -.I struct mount_attr -is -.BR MOUNT_ATTR_SIZE_VER0 . -.P -The -.I flags -argument can be used to alter the pathname resolution behavior. -The supported values are: -.TP -.B AT_EMPTY_PATH -If -.I pathname -is the empty string, -change the mount properties on -.I dirfd -itself. -.TP -.B AT_RECURSIVE -Change the mount properties of the entire mount tree. -.TP -.B AT_SYMLINK_NOFOLLOW -Don't follow trailing symbolic links. -.TP -.B AT_NO_AUTOMOUNT -Don't trigger automounts. -.P -The -.I attr -argument of -.BR mount_setattr () -is a structure of the following form: -.P -.in +4n -.EX -struct mount_attr { - __u64 attr_set; /* Mount properties to set */ - __u64 attr_clr; /* Mount properties to clear */ - __u64 propagation; /* Mount propagation type */ - __u64 userns_fd; /* User namespace file descriptor */ -}; -.EE -.in -.P -The -.I attr_set -and -.I attr_clr -members are used to specify the mount properties that -are supposed to be set or cleared for a mount or mount tree. -Flags set in -.I attr_set -enable a property on a mount or mount tree, -and flags set in -.I attr_clr -remove a property from a mount or mount tree. -.P -When changing mount properties, -the kernel will first clear the flags specified -in the -.I attr_clr -field, -and then set the flags specified in the -.I attr_set -field. -For example, these settings: -.P -.in +4n -.EX -struct mount_attr attr = { - .attr_clr = MOUNT_ATTR_NOEXEC | MOUNT_ATTR_NODEV, - .attr_set = MOUNT_ATTR_RDONLY | MOUNT_ATTR_NOSUID, -}; -.EE -.in -.P -are equivalent to the following steps: -.P -.in +4n -.EX -unsigned int current_mnt_flags = mnt\->mnt_flags; -\& -/* - * Clear all flags set in .attr_clr, - * clearing MOUNT_ATTR_NOEXEC and MOUNT_ATTR_NODEV. - */ -current_mnt_flags &= \(tiattr\->attr_clr; -\& -/* - * Now set all flags set in .attr_set, - * applying MOUNT_ATTR_RDONLY and MOUNT_ATTR_NOSUID. - */ -current_mnt_flags |= attr\->attr_set; -\& -mnt\->mnt_flags = current_mnt_flags; -.EE -.in -.P -As a result of this change, the mount or mount tree (a) is read-only; -(b) blocks the execution of set-user-ID and set-group-ID programs; -(c) allows execution of programs; and (d) allows access to devices. -.P -Multiple changes with the same set of flags requested -in -.I attr_clr -and -.I attr_set -are guaranteed to be idempotent after the changes have been applied. -.P -The following mount attributes can be specified in the -.I attr_set -or -.I attr_clr -fields: -.TP -.B MOUNT_ATTR_RDONLY -If set in -.IR attr_set , -makes the mount read-only. -If set in -.IR attr_clr , -removes the read-only setting if set on the mount. -.TP -.B MOUNT_ATTR_NOSUID -If set in -.IR attr_set , -causes the mount not to honor the set-user-ID and set-group-ID mode bits and -file capabilities when executing programs. -If set in -.IR attr_clr , -clears the set-user-ID, set-group-ID, -and file capability restriction if set on this mount. -.TP -.B MOUNT_ATTR_NODEV -If set in -.IR attr_set , -prevents access to devices on this mount. -If set in -.IR attr_clr , -removes the restriction that prevented accessing devices on this mount. -.TP -.B MOUNT_ATTR_NOEXEC -If set in -.IR attr_set , -prevents executing programs on this mount. -If set in -.IR attr_clr , -removes the restriction that prevented executing programs on this mount. -.TP -.B MOUNT_ATTR_NOSYMFOLLOW -If set in -.IR attr_set , -prevents following symbolic links on this mount. -If set in -.IR attr_clr , -removes the restriction that prevented following symbolic links on this mount. -.TP -.B MOUNT_ATTR_NODIRATIME -If set in -.IR attr_set , -prevents updating access time for directories on this mount. -If set in -.IR attr_clr , -removes the restriction that prevented updating access time for directories. -Note that -.B MOUNT_ATTR_NODIRATIME -can be combined with other access-time settings -and is implied by the noatime setting. -All other access-time settings are mutually exclusive. -.TP -.BR MOUNT_ATTR__ATIME " - changing access-time settings" -The access-time values listed below are an enumeration that -includes the value zero, expressed in the bits defined by the mask -.BR MOUNT_ATTR__ATIME . -Even though these bits are an enumeration -(in contrast to the other mount flags such as -.BR MOUNT_ATTR_NOEXEC ), -they are nonetheless passed in -.I attr_set -and -.I attr_clr -for consistency with -.BR fsmount (2), -which introduced this behavior. -.IP -Note that, -since the access-time values are an enumeration rather than bit values, -a caller wanting to transition to a different access-time setting -cannot simply specify the access-time setting in -.IR attr_set , -but must also include -.B MOUNT_ATTR__ATIME -in the -.I attr_clr -field. -The kernel will verify that -.B MOUNT_ATTR__ATIME -isn't partially set in -.I attr_clr -(i.e., either all bits in the -.B MOUNT_ATTR__ATIME -bit field are either set or clear), and that -.I attr_set -doesn't have any access-time bits set if -.B MOUNT_ATTR__ATIME -isn't set in -.IR attr_clr . -.RS -.TP -.B MOUNT_ATTR_RELATIME -When a file is accessed via this mount, -update the file's last access time (atime) -only if the current value of atime is less than or equal to -the file's last modification time (mtime) or last status change time (ctime). -.IP -To enable this access-time setting on a mount or mount tree, -.B MOUNT_ATTR_RELATIME -must be set in -.I attr_set -and -.B MOUNT_ATTR__ATIME -must be set in the -.I attr_clr -field. -.TP -.B MOUNT_ATTR_NOATIME -Do not update access times for (all types of) files on this mount. -.IP -To enable this access-time setting on a mount or mount tree, -.B MOUNT_ATTR_NOATIME -must be set in -.I attr_set -and -.B MOUNT_ATTR__ATIME -must be set in the -.I attr_clr -field. -.TP -.B MOUNT_ATTR_STRICTATIME -Always update the last access time (atime) -when files are accessed on this mount. -.IP -To enable this access-time setting on a mount or mount tree, -.B MOUNT_ATTR_STRICTATIME -must be set in -.I attr_set -and -.B MOUNT_ATTR__ATIME -must be set in the -.I attr_clr -field. -.RE -.TP -.B MOUNT_ATTR_IDMAP -If set in -.IR attr_set , -creates an ID-mapped mount. -The ID mapping is taken from the user namespace specified in -.I userns_fd -and attached to the mount. -.IP -Since it is not supported to -change the ID mapping of a mount after it has been ID mapped, -it is invalid to specify -.B MOUNT_ATTR_IDMAP -in -.IR attr_clr . -.IP -For further details, see the subsection "ID-mapped mounts" under NOTES. -.P -The -.I propagation -field is used to specify the propagation type of the mount or mount tree. -This field either has the value zero, -meaning leave the propagation type unchanged, or it has one of -the following values: -.TP -.B MS_PRIVATE -Turn all mounts into private mounts. -.TP -.B MS_SHARED -Turn all mounts into shared mounts. -.TP -.B MS_SLAVE -Turn all mounts into dependent mounts. -.TP -.B MS_UNBINDABLE -Turn all mounts into unbindable mounts. -.P -For further details on the above propagation types, see -.BR mount_namespaces (7). -.SH RETURN VALUE -On success, -.BR mount_setattr () -returns zero. -On error, -\-1 is returned and -.I errno -is set to indicate the cause of the error. -.SH ERRORS -.TP -.B EBADF -.I pathname -is relative but -.I dirfd -is neither -.B AT_FDCWD -nor a valid file descriptor. -.TP -.B EBADF -.I userns_fd -is not a valid file descriptor. -.TP -.B EBUSY -The caller tried to change the mount to -.BR MOUNT_ATTR_RDONLY , -but the mount still holds files open for writing. -.TP -.B EBUSY -The caller tried to create an ID-mapped mount raising -.B MOUNT_ATTR_IDMAP -and specifying -.I userns_fd -but the mount still holds files open for writing. -.TP -.B EINVAL -The pathname specified via the -.I dirfd -and -.I pathname -arguments to -.BR mount_setattr () -isn't a mount point. -.TP -.B EINVAL -An unsupported value was set in -.IR flags . -.TP -.B EINVAL -An unsupported value was specified in the -.I attr_set -field of -.IR mount_attr . -.TP -.B EINVAL -An unsupported value was specified in the -.I attr_clr -field of -.IR mount_attr . -.TP -.B EINVAL -An unsupported value was specified in the -.I propagation -field of -.IR mount_attr . -.TP -.B EINVAL -More than one of -.BR MS_SHARED , -.BR MS_SLAVE , -.BR MS_PRIVATE , -or -.B MS_UNBINDABLE -was set in the -.I propagation -field of -.IR mount_attr . -.TP -.B EINVAL -An access-time setting was specified in the -.I attr_set -field without -.B MOUNT_ATTR__ATIME -being set in the -.I attr_clr -field. -.TP -.B EINVAL -.B MOUNT_ATTR_IDMAP -was specified in -.IR attr_clr . -.TP -.B EINVAL -A file descriptor value was specified in -.I userns_fd -which exceeds -.BR INT_MAX . -.TP -.B EINVAL -A valid file descriptor value was specified in -.IR userns_fd , -but the file descriptor did not refer to a user namespace. -.TP -.B EINVAL -The underlying filesystem does not support ID-mapped mounts. -.TP -.B EINVAL -The mount that is to be ID mapped is not a detached mount; -that is, the mount has not previously been visible in a mount namespace. -.TP -.B EINVAL -A partial access-time setting was specified in -.I attr_clr -instead of -.B MOUNT_ATTR__ATIME -being set. -.TP -.B EINVAL -The mount is located outside the caller's mount namespace. -.TP -.B EINVAL -The underlying filesystem has been mounted in a mount namespace that is -owned by a noninitial user namespace -.TP -.B ENOENT -A pathname was empty or had a nonexistent component. -.TP -.B ENOMEM -When changing mount propagation to -.BR MS_SHARED , -a new peer group ID needs to be allocated for all mounts without a peer group -ID set. -This allocation failed because there was not -enough memory to allocate the relevant internal structures. -.TP -.B ENOSPC -When changing mount propagation to -.BR MS_SHARED , -a new peer group ID needs to be allocated for all mounts without a peer group -ID set. -This allocation failed because -the kernel has run out of IDs. -.\" Christian Brauner: i.e. someone has somehow managed to -.\" allocate so many peer groups and managed to keep the kernel running -.\" (???) that the ida has ran out of ids -.\" Note that technically further error codes are possible that are -.\" specific to the ID allocation implementation used. -.TP -.B EPERM -One of the mounts had at least one of -.BR MOUNT_ATTR_NOATIME , -.BR MOUNT_ATTR_NODEV , -.BR MOUNT_ATTR_NODIRATIME , -.BR MOUNT_ATTR_NOEXEC , -.BR MOUNT_ATTR_NOSUID , -or -.B MOUNT_ATTR_RDONLY -set and the flag is locked. -Mount attributes become locked on a mount if: -.RS -.IP \[bu] 3 -A new mount or mount tree is created causing mount propagation across user -namespaces -(i.e., propagation to a mount namespace owned by a different user namespace). -The kernel will lock the aforementioned flags to prevent these sensitive -properties from being altered. -.IP \[bu] -A new mount and user namespace pair is created. -This happens for example when specifying -.B CLONE_NEWUSER | CLONE_NEWNS -in -.BR unshare (2), -.BR clone (2), -or -.BR clone3 (2). -The aforementioned flags become locked in the new mount namespace -to prevent sensitive mount properties from being altered. -Since the newly created mount namespace will be owned by the -newly created user namespace, -a calling process that is privileged in the new -user namespace would\[em]in the absence of such locking\[em]be -able to alter sensitive mount properties (e.g., to remount a mount -that was marked read-only as read-write in the new mount namespace). -.RE -.TP -.B EPERM -A valid file descriptor value was specified in -.IR userns_fd , -but the file descriptor refers to the initial user namespace. -.TP -.B EPERM -An attempt was made to add an ID mapping to a mount that is already ID mapped. -.TP -.B EPERM -The caller does not have -.B CAP_SYS_ADMIN -in the initial user namespace. -.SH STANDARDS -Linux. -.SH HISTORY -Linux 5.12. -.\" commit 7d6beb71da3cc033649d641e1e608713b8220290 -.\" commit 2a1867219c7b27f928e2545782b86daaf9ad50bd -.\" commit 9caccd41541a6f7d6279928d9f971f6642c361af -.SH NOTES -.SS ID-mapped mounts -Creating an ID-mapped mount makes it possible to -change the ownership of all files located under a mount. -Thus, ID-mapped mounts make it possible to -change ownership in a temporary and localized way. -It is a localized change because the ownership changes are -visible only via a specific mount. -All other users and locations where the filesystem is exposed are unaffected. -It is a temporary change because -the ownership changes are tied to the lifetime of the mount. -.P -Whenever callers interact with the filesystem through an ID-mapped mount, -the ID mapping of the mount will be applied to -user and group IDs associated with filesystem objects. -This encompasses the user and group IDs associated with inodes -and also the following -.BR xattr (7) -keys: -.IP \[bu] 3 -.IR security.capability , -whenever filesystem capabilities -are stored or returned in the -.B VFS_CAP_REVISION_3 -format, -which stores a root user ID alongside the capabilities -(see -.BR capabilities (7)). -.IP \[bu] -.I system.posix_acl_access -and -.IR system.posix_acl_default , -whenever user IDs or group IDs are stored in -.B ACL_USER -or -.B ACL_GROUP -entries. -.P -The following conditions must be met in order to create an ID-mapped mount: -.IP \[bu] 3 -The caller must have the -.B CAP_SYS_ADMIN -capability in the user namespace the filesystem was mounted in. -.\" commit bd303368b776eead1c29e6cdda82bde7128b82a7 -.\" Christian Brauner -.\" Note, currently no filesystems mountable in non-initial user namespaces -.\" support ID-mapped mounts. -.IP \[bu] -The underlying filesystem must support ID-mapped mounts. -Currently, the following filesystems support ID-mapped mounts: -.\" fs_flags = FS_ALLOW_IDMAP in kernel sources -.RS -.IP \[bu] 3 -.PD 0 -.BR xfs (5) -(since Linux 5.12) -.IP \[bu] -.BR ext4 (5) -(since Linux 5.12) -.IP \[bu] -.B FAT -(since Linux 5.12) -.IP \[bu] -.BR btrfs (5) -(since Linux 5.15) -.\" commit 5b9b26f5d0b88b74001dcfe4ab8a8f2f4e744112 -.IP \[bu] -.B ntfs3 -(since Linux 5.15) -.\" commit 82cae269cfa953032fbb8980a7d554d60fb00b17 -.IP \[bu] -.B f2fs -(since Linux 5.18) -.\" commit 984fc4e76d63345499f01c0c198a4b44860cf027 -.IP \[bu] -.B erofs -(since Linux 5.19) -.\" commit 6c459b78d4793afbba6d864c466cc5cd2932459d -.IP \[bu] -.B overlayfs -(ID-mapped lower and upper layers supported since Linux 5.19) -.PD -.RE -.IP \[bu] -The mount must not already be ID-mapped. -This also implies that the ID mapping of a mount cannot be altered. -.IP \[bu] -The mount must not have any writers. -.\" commit 1bbcd277a53e08d619ffeec56c5c9287f2bf42f -.IP \[bu] -The mount must be a detached mount; -that is, -it must have been created by calling -.BR open_tree (2) -with the -.B OPEN_TREE_CLONE -flag and it must not already have been visible in a mount namespace. -(To put things another way: -the mount must not have been attached to the filesystem hierarchy -with a system call such as -.BR move_mount (2).) -.P -ID mappings can be created for user IDs, group IDs, and project IDs. -An ID mapping is essentially a mapping of a range of user or group IDs into -another or the same range of user or group IDs. -ID mappings are written to map files as three numbers -separated by white space. -The first two numbers specify the starting user or group ID -in each of the two user namespaces. -The third number specifies the range of the ID mapping. -For example, -a mapping for user IDs such as "1000\ 1001\ 1" would indicate that -user ID 1000 in the caller's user namespace is mapped to -user ID 1001 in its ancestor user namespace. -Since the map range is 1, -only user ID 1000 is mapped. -.P -It is possible to specify up to 340 ID mappings for each ID mapping type. -If any user IDs or group IDs are not mapped, -all files owned by that unmapped user or group ID will appear as -being owned by the overflow user ID or overflow group ID respectively. -.P -Further details on setting up ID mappings can be found in -.BR user_namespaces (7). -.P -In the common case, the user namespace passed in -.I userns_fd -(together with -.B MOUNT_ATTR_IDMAP -in -.IR attr_set ) -to create an ID-mapped mount will be the user namespace of a container. -In other scenarios it will be a dedicated user namespace associated with -a user's login session as is the case for portable home directories in -.BR systemd-homed.service (8)). -It is also perfectly fine to create a dedicated user namespace -for the sake of ID mapping a mount. -.P -ID-mapped mounts can be useful in the following -and a variety of other scenarios: -.IP \[bu] 3 -Sharing files or filesystems -between multiple users or multiple machines, -especially in complex scenarios. -For example, -ID-mapped mounts are used to implement portable home directories in -.BR systemd-homed.service (8), -where they allow users to move their home directory -to an external storage device -and use it on multiple computers -where they are assigned different user IDs and group IDs. -This effectively makes it possible to -assign random user IDs and group IDs at login time. -.IP \[bu] -Sharing files or filesystems -from the host with unprivileged containers. -This allows a user to avoid having to change ownership permanently through -.BR chown (2). -.IP \[bu] -ID mapping a container's root filesystem. -Users don't need to change ownership permanently through -.BR chown (2). -Especially for large root filesystems, using -.BR chown (2) -can be prohibitively expensive. -.IP \[bu] -Sharing files or filesystems -between containers with non-overlapping ID mappings. -.IP \[bu] -Implementing discretionary access (DAC) permission checking -for filesystems lacking a concept of ownership. -.IP \[bu] -Efficiently changing ownership on a per-mount basis. -In contrast to -.BR chown (2), -changing ownership of large sets of files is instantaneous with -ID-mapped mounts. -This is especially useful when ownership of -an entire root filesystem of a virtual machine or container -is to be changed as mentioned above. -With ID-mapped mounts, -a single -.BR mount_setattr () -system call will be sufficient to change the ownership of all files. -.IP \[bu] -Taking the current ownership into account. -ID mappings specify precisely -what a user or group ID is supposed to be mapped to. -This contrasts with the -.BR chown (2) -system call which cannot by itself -take the current ownership of the files it changes into account. -It simply changes the ownership to the specified user ID and group ID. -.IP \[bu] -Locally and temporarily restricted ownership changes. -ID-mapped mounts make it possible to change ownership locally, -restricting the ownership changes to specific mounts, -and temporarily as the ownership changes only apply as long as the mount exists. -By contrast, -changing ownership via the -.BR chown (2) -system call changes the ownership globally and permanently. -.\" -.SS Extensibility -In order to allow for future extensibility, -.BR mount_setattr () -requires the user-space application to specify the size of the -.I mount_attr -structure that it is passing. -By providing this information, it is possible for -.BR mount_setattr () -to provide both forwards- and backwards-compatibility, with -.I size -acting as an implicit version number. -(Because new extension fields will always -be appended, the structure size will always increase.) -This extensibility design is very similar to other system calls such as -.BR perf_setattr (2), -.BR perf_event_open (2), -.BR clone3 (2) -and -.BR openat2 (2). -.P -Let -.I usize -be the size of the structure as specified by the user-space application, -and let -.I ksize -be the size of the structure which the kernel supports, -then there are three cases to consider: -.IP \[bu] 3 -If -.I ksize -equals -.IR usize , -then there is no version mismatch and -.I attr -can be used verbatim. -.IP \[bu] -If -.I ksize -is larger than -.IR usize , -then there are some extension fields that the kernel supports -which the user-space application is unaware of. -Because a zero value in any added extension field signifies a no-op, -the kernel treats all of the extension fields -not provided by the user-space application -as having zero values. -This provides backwards-compatibility. -.IP \[bu] -If -.I ksize -is smaller than -.IR usize , -then there are some extension fields which the user-space application is aware -of but which the kernel does not support. -Because any extension field must have its zero values signify a no-op, -the kernel can safely ignore the unsupported extension fields -if they are all zero. -If any unsupported extension fields are non-zero, -then \-1 is returned and -.I errno -is set to -.BR E2BIG . -This provides forwards-compatibility. -.P -Because the definition of -.I struct mount_attr -may change in the future -(with new fields being added when system headers are updated), -user-space applications should zero-fill -.I struct mount_attr -to ensure that recompiling the program with new headers will not result in -spurious errors at run time. -The simplest way is to use a designated initializer: -.P -.in +4n -.EX -struct mount_attr attr = { - .attr_set = MOUNT_ATTR_RDONLY, - .attr_clr = MOUNT_ATTR_NODEV -}; -.EE -.in -.P -Alternatively, the structure can be zero-filled using -.BR memset (3) -or similar functions: -.P -.in +4n -.EX -struct mount_attr attr; -memset(&attr, 0, sizeof(attr)); -attr.attr_set = MOUNT_ATTR_RDONLY; -attr.attr_clr = MOUNT_ATTR_NODEV; -.EE -.in -.P -A user-space application that wishes to determine which extensions the running -kernel supports can do so by conducting a binary search on -.I size -with a structure which has every byte nonzero -(to find the largest value which doesn't produce an error of -.BR E2BIG ). -.SH EXAMPLES -.\" SRC BEGIN (mount_setattr.c) -.EX -/* - * This program allows the caller to create a new detached mount - * and set various properties on it. - */ -#define _GNU_SOURCE -#include <err.h> -#include <fcntl.h> -#include <getopt.h> -#include <linux/mount.h> -#include <linux/types.h> -#include <stdbool.h> -#include <stdio.h> -#include <stdlib.h> -#include <string.h> -#include <sys/syscall.h> -#include <unistd.h> -\& -static inline int -mount_setattr(int dirfd, const char *pathname, unsigned int flags, - struct mount_attr *attr, size_t size) -{ - return syscall(SYS_mount_setattr, dirfd, pathname, flags, - attr, size); -} -\& -static inline int -open_tree(int dirfd, const char *filename, unsigned int flags) -{ - return syscall(SYS_open_tree, dirfd, filename, flags); -} -\& -static inline int -move_mount(int from_dirfd, const char *from_pathname, - int to_dirfd, const char *to_pathname, unsigned int flags) -{ - return syscall(SYS_move_mount, from_dirfd, from_pathname, - to_dirfd, to_pathname, flags); -} -\& -static const struct option longopts[] = { - {"map\-mount", required_argument, NULL, \[aq]a\[aq]}, - {"recursive", no_argument, NULL, \[aq]b\[aq]}, - {"read\-only", no_argument, NULL, \[aq]c\[aq]}, - {"block\-setid", no_argument, NULL, \[aq]d\[aq]}, - {"block\-devices", no_argument, NULL, \[aq]e\[aq]}, - {"block\-exec", no_argument, NULL, \[aq]f\[aq]}, - {"no\-access\-time", no_argument, NULL, \[aq]g\[aq]}, - { NULL, 0, NULL, 0 }, -}; -\& -int -main(int argc, char *argv[]) -{ - int fd_userns = \-1; - int fd_tree; - int index = 0; - int ret; - bool recursive = false; - const char *source; - const char *target; - struct mount_attr *attr = &(struct mount_attr){}; -\& - while ((ret = getopt_long_only(argc, argv, "", - longopts, &index)) != \-1) { - switch (ret) { - case \[aq]a\[aq]: - fd_userns = open(optarg, O_RDONLY | O_CLOEXEC); - if (fd_userns == \-1) - err(EXIT_FAILURE, "open(%s)", optarg); - break; - case \[aq]b\[aq]: - recursive = true; - break; - case \[aq]c\[aq]: - attr\->attr_set |= MOUNT_ATTR_RDONLY; - break; - case \[aq]d\[aq]: - attr\->attr_set |= MOUNT_ATTR_NOSUID; - break; - case \[aq]e\[aq]: - attr\->attr_set |= MOUNT_ATTR_NODEV; - break; - case \[aq]f\[aq]: - attr\->attr_set |= MOUNT_ATTR_NOEXEC; - break; - case \[aq]g\[aq]: - attr\->attr_set |= MOUNT_ATTR_NOATIME; - attr\->attr_clr |= MOUNT_ATTR__ATIME; - break; - default: - errx(EXIT_FAILURE, "Invalid argument specified"); - } - } -\& - if ((argc \- optind) < 2) - errx(EXIT_FAILURE, "Missing source or target mount point"); -\& - source = argv[optind]; - target = argv[optind + 1]; -\& - /* In the following, \-1 as the \[aq]dirfd\[aq] argument ensures that - open_tree() fails if \[aq]source\[aq] is not an absolute pathname. */ -.\" Christian Brauner -.\" When writing programs I like to never use relative paths with AT_FDCWD -.\" because. Because making assumptions about the current working directory -.\" of the calling process is just too easy to get wrong; especially when -.\" pivot_root() or chroot() are in play. -.\" My absolut preference (joke intended) is to open a well-known starting -.\" point with an absolute path to get a dirfd and then scope all future -.\" operations beneath that dirfd. This already works with old-style -.\" openat() and _very_ cautious programming but openat2() and its -.\" resolve-flag space have made this **chef's kiss**. -.\" If I can't operate based on a well-known dirfd I use absolute paths -.\" with a -EBADF dirfd passed to *at() functions. -\& - fd_tree = open_tree(\-1, source, - OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC | - AT_EMPTY_PATH | (recursive ? AT_RECURSIVE : 0)); - if (fd_tree == \-1) - err(EXIT_FAILURE, "open(%s)", source); -\& - if (fd_userns >= 0) { - attr\->attr_set |= MOUNT_ATTR_IDMAP; - attr\->userns_fd = fd_userns; - } -\& - ret = mount_setattr(fd_tree, "", - AT_EMPTY_PATH | (recursive ? AT_RECURSIVE : 0), - attr, sizeof(struct mount_attr)); - if (ret == \-1) - err(EXIT_FAILURE, "mount_setattr"); -\& - close(fd_userns); -\& - /* In the following, \-1 as the \[aq]to_dirfd\[aq] argument ensures that - open_tree() fails if \[aq]target\[aq] is not an absolute pathname. */ -\& - ret = move_mount(fd_tree, "", \-1, target, - MOVE_MOUNT_F_EMPTY_PATH); - if (ret == \-1) - err(EXIT_FAILURE, "move_mount() to %s", target); -\& - close(fd_tree); -\& - exit(EXIT_SUCCESS); -} -.EE -.\" SRC END -.SH SEE ALSO -.BR newgidmap (1), -.BR newuidmap (1), -.BR clone (2), -.BR mount (2), -.BR unshare (2), -.BR proc (5), -.BR capabilities (7), -.BR mount_namespaces (7), -.BR user_namespaces (7), -.BR xattr (7) |