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Date:   Sun, 15 Nov 2020 11:36:43 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel@...r.kernel.org
Cc:     John Johansen <john.johansen@...onical.com>,
        James Morris <jmorris@...ei.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        Geoffrey Thomas <geofft@...reload.com>,
        Mrunal Patel <mpatel@...hat.com>,
        Josh Triplett <josh@...htriplett.org>,
        Andy Lutomirski <luto@...nel.org>,
        Theodore Tso <tytso@....edu>, Alban Crequy <alban@...volk.io>,
        Tycho Andersen <tycho@...ho.ws>,
        David Howells <dhowells@...hat.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Jann Horn <jannh@...gle.com>,
        Seth Forshee <seth.forshee@...onical.com>,
        St├ęphane Graber <stgraber@...ntu.com>,
        Aleksa Sarai <cyphar@...har.com>,
        Lennart Poettering <lennart@...ttering.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, smbarber@...omium.org,
        Phil Estes <estesp@...il.com>, Serge Hallyn <serge@...lyn.com>,
        Kees Cook <keescook@...omium.org>,
        Todd Kjos <tkjos@...gle.com>, Jonathan Corbet <corbet@....net>,
        containers@...ts.linux-foundation.org,
        linux-security-module@...r.kernel.org, linux-api@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-audit@...hat.com,
        linux-integrity@...r.kernel.org, selinux@...r.kernel.org,
        Christian Brauner <christian.brauner@...ntu.com>,
        Christoph Hellwig <hch@....de>
Subject: [PATCH v2 04/39] fs: add mount_setattr()

This implements the mount_setattr() syscall. While the new mount api
allows to change the properties of a superblock there is currently no
way to change the mount properties of a mount or mount tree using file
descriptors which the new mount api is based on. In addition the old mount api
has the restriction that mount options cannot be applied recursively. This
hasn't changed since changing mount options on a per-mount basis was implemented
in [1] and has been a frequent request.
The legacy mount is currently unable to accommodate this behavior without
introducing a whole new set of flags because MS_REC | MS_REMOUNT | MS_BIND |
MS_RDONLY | MS_NOEXEC | [...] only apply the mount option to the topmost mount.
Changing MS_REC to apply to the whole mount tree would mean introducing a
significant uapi change and would likely cause significant regressions.

The new mount_setattr() syscall allows to recursively clear and set mount
options in one shot. Multiple calls to change mount options requesting the same
changes are idempotent:

int mount_setattr(int dfd, const char *path, unsigned flags,
                  struct mount_attr *uattr, size_t usize);

Flags to modify path resolution behavior are specified in the @flags argument.
Currently, AT_EMPTY_PATH, AT_RECURSIVE, AT_SYMLINK_NOFOLLOW, and AT_NO_AUTOMOUNT
are supported. If useful, additional lookup flags to restrict path resolution as
introduced with openat2() might be supported in the future.

mount_setattr() can be expected to grow over time and is designed with
extensibility in mind. It follows the extensible syscall pattern we have used
with other syscalls such as openat2(), clone3(), sched_{set,get}attr(), and
others.
The set of mount options is passed in the uapi struct mount_attr which currently
has the following layout:

struct mount_attr {
	__u64 attr_set;
	__u64 attr_clr;
	__u32 propagation;
};

The @attr_set and @attr_clr members are used to clear and set mount options.
This way a user can e.g. request that a set of flags is to be raised such as
turning mounts readonly by raising MOUNT_ATTR_RDONLY in @attr_set while at the
same time requesting that another set of flags is to be lowered such as removing
noexec from a mount tree by specifying MOUNT_ATTR_NOEXEC in @attr_clr.

Note, since the MOUNT_ATTR_<atime> values are an enum starting from 0, not a
bitmap, users wanting to transition to a different atime setting cannot simply
specify the atime setting in @attr_set, but must also specify MOUNT_ATTR__ATIME
in the @attr_clr field. So we ensure that MOUNT_ATTR__ATIME can't be partially
set in @attr_clr and that @attr_set can't have any atime bits set if
MOUNT_ATTR__ATIME isn't set in @attr_clr.

The @propagation field lets callers specify the propagation type of a mount
tree. Propagation is a single property that has four different settings and as
such is not really a flag argument but an enum.  Specifically, it would be
unclear what setting and clearing propagation settings in combination would
amount to. The legacy mount() syscall thus forbids the combination of multiple
propagation settings too. The goal is to keep the semantics of mount propagation
somewhat simple as they are overly complex as it is.

[1]: commit 2e4b7fcd9260 ("[PATCH] r/o bind mounts: honor mount writer counts at remount")
Cc: Christoph Hellwig <hch@....de>
Cc: David Howells <dhowells@...hat.com>
Cc: Aleksa Sarai <cyphar@...har.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: linux-fsdevel@...r.kernel.org
Cc: linux-api@...r.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
---
/* v2 */
- Christoph Hellwig:
  - Split into multiple helpers.
---
 arch/alpha/kernel/syscalls/syscall.tbl      |   1 +
 arch/arm/tools/syscall.tbl                  |   1 +
 arch/arm64/include/asm/unistd32.h           |   2 +
 arch/ia64/kernel/syscalls/syscall.tbl       |   1 +
 arch/m68k/kernel/syscalls/syscall.tbl       |   1 +
 arch/microblaze/kernel/syscalls/syscall.tbl |   1 +
 arch/mips/kernel/syscalls/syscall_n32.tbl   |   1 +
 arch/mips/kernel/syscalls/syscall_n64.tbl   |   1 +
 arch/mips/kernel/syscalls/syscall_o32.tbl   |   1 +
 arch/parisc/kernel/syscalls/syscall.tbl     |   1 +
 arch/powerpc/kernel/syscalls/syscall.tbl    |   1 +
 arch/s390/kernel/syscalls/syscall.tbl       |   1 +
 arch/sh/kernel/syscalls/syscall.tbl         |   1 +
 arch/sparc/kernel/syscalls/syscall.tbl      |   1 +
 arch/x86/entry/syscalls/syscall_32.tbl      |   1 +
 arch/x86/entry/syscalls/syscall_64.tbl      |   1 +
 arch/xtensa/kernel/syscalls/syscall.tbl     |   1 +
 fs/internal.h                               |   8 +
 fs/namespace.c                              | 325 ++++++++++++++++++--
 include/linux/syscalls.h                    |   3 +
 include/uapi/asm-generic/unistd.h           |   4 +-
 include/uapi/linux/mount.h                  |  22 ++
 tools/include/uapi/asm-generic/unistd.h     |   4 +-
 23 files changed, 358 insertions(+), 26 deletions(-)

diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index ee7b01bb7346..24d8709624b8 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@ -480,3 +480,4 @@
 548	common	pidfd_getfd			sys_pidfd_getfd
 549	common	faccessat2			sys_faccessat2
 550	common	process_madvise			sys_process_madvise
+551	common	mount_setattr			sys_mount_setattr
diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index d056a548358e..e3785513d445 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@ -454,3 +454,4 @@
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	process_madvise			sys_process_madvise
+441	common	mount_setattr			sys_mount_setattr
diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h
index 107f08e03b9f..78af754e070a 100644
--- a/arch/arm64/include/asm/unistd32.h
+++ b/arch/arm64/include/asm/unistd32.h
@@ -889,6 +889,8 @@ __SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
 __SYSCALL(__NR_faccessat2, sys_faccessat2)
 #define __NR_process_madvise 440
 __SYSCALL(__NR_process_madvise, sys_process_madvise)
+#define __NR_mount_setattr 441
+__SYSCALL(__NR_mount_setattr, sys_mount_setattr)
 
 /*
  * Please add new compat syscalls above this comment and update
diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl
index b96ed8b8a508..f7d4b1f55be0 100644
--- a/arch/ia64/kernel/syscalls/syscall.tbl
+++ b/arch/ia64/kernel/syscalls/syscall.tbl
@@ -361,3 +361,4 @@
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	process_madvise			sys_process_madvise
+441	common	mount_setattr			sys_mount_setattr
diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index 625fb6d32842..e96e9c6a6ffa 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -440,3 +440,4 @@
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	process_madvise			sys_process_madvise
+441	common	mount_setattr			sys_mount_setattr
diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index aae729c95cf9..6538f075a18e 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@ -446,3 +446,4 @@
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	process_madvise			sys_process_madvise
+441	common	mount_setattr			sys_mount_setattr
diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
index 32817c954435..64d129db1aa7 100644
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
@@ -379,3 +379,4 @@
 438	n32	pidfd_getfd			sys_pidfd_getfd
 439	n32	faccessat2			sys_faccessat2
 440	n32	process_madvise			sys_process_madvise
+441	n32	mount_setattr			sys_mount_setattr
diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
index 9e4ea3c31b1c..94b24e6b2608 100644
--- a/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
@@ -355,3 +355,4 @@
 438	n64	pidfd_getfd			sys_pidfd_getfd
 439	n64	faccessat2			sys_faccessat2
 440	n64	process_madvise			sys_process_madvise
+441	n64	mount_setattr			sys_mount_setattr
diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
index 29f5f28cf5ce..eae522306767 100644
--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
@@ -428,3 +428,4 @@
 438	o32	pidfd_getfd			sys_pidfd_getfd
 439	o32	faccessat2			sys_faccessat2
 440	o32	process_madvise			sys_process_madvise
+441	o32	mount_setattr			sys_mount_setattr
diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
index f375ea528e59..c7e25f1d219f 100644
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl
@@ -438,3 +438,4 @@
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	process_madvise			sys_process_madvise
+441	common	mount_setattr			sys_mount_setattr
diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
index 1275daec7fec..0b309ef64e91 100644
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@ -530,3 +530,4 @@
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	process_madvise			sys_process_madvise
+441	common	mount_setattr			sys_mount_setattr
diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
index 28c168000483..0b30398fee42 100644
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl
@@ -443,3 +443,4 @@
 438  common	pidfd_getfd		sys_pidfd_getfd			sys_pidfd_getfd
 439  common	faccessat2		sys_faccessat2			sys_faccessat2
 440  common	process_madvise		sys_process_madvise		sys_process_madvise
+441  common	mount_setattr		sys_mount_setattr		sys_mount_setattr
diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
index 783738448ff5..8e4949c5b740 100644
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl
@@ -443,3 +443,4 @@
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	process_madvise			sys_process_madvise
+441	common	mount_setattr			sys_mount_setattr
diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
index 78160260991b..409f21a650b8 100644
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl
@@ -486,3 +486,4 @@
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	process_madvise			sys_process_madvise
+441	common	mount_setattr			sys_mount_setattr
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 0d0667a9fbd7..2a694420f6cd 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -445,3 +445,4 @@
 438	i386	pidfd_getfd		sys_pidfd_getfd
 439	i386	faccessat2		sys_faccessat2
 440	i386	process_madvise		sys_process_madvise
+441	i386	mount_setattr		sys_mount_setattr
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 379819244b91..4d594d0246c1 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -362,6 +362,7 @@
 438	common	pidfd_getfd		sys_pidfd_getfd
 439	common	faccessat2		sys_faccessat2
 440	common	process_madvise		sys_process_madvise
+441	common	mount_setattr		sys_mount_setattr
 
 #
 # Due to a historical design error, certain syscalls are numbered differently
diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
index b070f272995d..a650dc05593d 100644
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl
@@ -411,3 +411,4 @@
 438	common	pidfd_getfd			sys_pidfd_getfd
 439	common	faccessat2			sys_faccessat2
 440	common	process_madvise			sys_process_madvise
+441	common	mount_setattr			sys_mount_setattr
diff --git a/fs/internal.h b/fs/internal.h
index a7cd0f64faa4..a5a6c470dc07 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -82,6 +82,14 @@ int may_linkat(struct path *link);
 /*
  * namespace.c
  */
+struct mount_kattr {
+	unsigned int attr_set;
+	unsigned int attr_clr;
+	unsigned int propagation;
+	unsigned int lookup_flags;
+	bool recurse;
+};
+
 extern struct vfsmount *lookup_mnt(const struct path *);
 extern int finish_automount(struct vfsmount *, struct path *);
 
diff --git a/fs/namespace.c b/fs/namespace.c
index 8497d149ecaa..9fc8b22dba26 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -469,10 +469,8 @@ void mnt_drop_write_file(struct file *file)
 }
 EXPORT_SYMBOL(mnt_drop_write_file);
 
-static int mnt_make_readonly(struct mount *mnt)
+static inline int mnt_hold_writers(struct mount *mnt)
 {
-	int ret = 0;
-
 	mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
 	/*
 	 * After storing MNT_WRITE_HOLD, we'll read the counters. This store
@@ -497,15 +495,29 @@ static int mnt_make_readonly(struct mount *mnt)
 	 * we're counting up here.
 	 */
 	if (mnt_get_writers(mnt) > 0)
-		ret = -EBUSY;
-	else
-		mnt->mnt.mnt_flags |= MNT_READONLY;
+		return -EBUSY;
+
+	return 0;
+}
+
+static inline void mnt_unhold_writers(struct mount *mnt)
+{
 	/*
 	 * MNT_READONLY must become visible before ~MNT_WRITE_HOLD, so writers
 	 * that become unheld will see MNT_READONLY.
 	 */
 	smp_wmb();
 	mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
+}
+
+static int mnt_make_readonly(struct mount *mnt)
+{
+	int ret;
+
+	ret = mnt_hold_writers(mnt);
+	if (!ret)
+		mnt->mnt.mnt_flags |= MNT_READONLY;
+	mnt_unhold_writers(mnt);
 	return ret;
 }
 
@@ -3438,6 +3450,33 @@ SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
 	return ret;
 }
 
+static int build_attr_flags(unsigned int attr_flags, unsigned int *flags)
+{
+	unsigned int aflags = 0;
+
+	if (attr_flags & ~(MOUNT_ATTR_RDONLY |
+			   MOUNT_ATTR_NOSUID |
+			   MOUNT_ATTR_NODEV |
+			   MOUNT_ATTR_NOEXEC |
+			   MOUNT_ATTR__ATIME |
+			   MOUNT_ATTR_NODIRATIME))
+		return -EINVAL;
+
+	if (attr_flags & MOUNT_ATTR_RDONLY)
+		aflags |= MNT_READONLY;
+	if (attr_flags & MOUNT_ATTR_NOSUID)
+		aflags |= MNT_NOSUID;
+	if (attr_flags & MOUNT_ATTR_NODEV)
+		aflags |= MNT_NODEV;
+	if (attr_flags & MOUNT_ATTR_NOEXEC)
+		aflags |= MNT_NOEXEC;
+	if (attr_flags & MOUNT_ATTR_NODIRATIME)
+		aflags |= MNT_NODIRATIME;
+
+	*flags = aflags;
+	return 0;
+}
+
 /*
  * Create a kernel mount representation for a new, prepared superblock
  * (specified by fs_fd) and attach to an open_tree-like file descriptor.
@@ -3460,24 +3499,9 @@ SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags,
 	if ((flags & ~(FSMOUNT_CLOEXEC)) != 0)
 		return -EINVAL;
 
-	if (attr_flags & ~(MOUNT_ATTR_RDONLY |
-			   MOUNT_ATTR_NOSUID |
-			   MOUNT_ATTR_NODEV |
-			   MOUNT_ATTR_NOEXEC |
-			   MOUNT_ATTR__ATIME |
-			   MOUNT_ATTR_NODIRATIME))
-		return -EINVAL;
-
-	if (attr_flags & MOUNT_ATTR_RDONLY)
-		mnt_flags |= MNT_READONLY;
-	if (attr_flags & MOUNT_ATTR_NOSUID)
-		mnt_flags |= MNT_NOSUID;
-	if (attr_flags & MOUNT_ATTR_NODEV)
-		mnt_flags |= MNT_NODEV;
-	if (attr_flags & MOUNT_ATTR_NOEXEC)
-		mnt_flags |= MNT_NOEXEC;
-	if (attr_flags & MOUNT_ATTR_NODIRATIME)
-		mnt_flags |= MNT_NODIRATIME;
+	ret = build_attr_flags(attr_flags, &mnt_flags);
+	if (ret)
+		return ret;
 
 	switch (attr_flags & MOUNT_ATTR__ATIME) {
 	case MOUNT_ATTR_STRICTATIME:
@@ -3785,6 +3809,259 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
 	return error;
 }
 
+static unsigned int recalc_flags(struct mount_kattr *kattr, struct mount *mnt)
+{
+	unsigned int flags = mnt->mnt.mnt_flags;
+
+	/*  flags to clear */
+	flags &= ~kattr->attr_clr;
+	/* flags to raise */
+	flags |= kattr->attr_set;
+
+	return flags;
+}
+
+static struct mount *mount_setattr_prepare(struct mount_kattr *kattr,
+					   struct mount *mnt, int *err)
+{
+	struct mount *m = mnt, *last = NULL;
+
+	if (!is_mounted(&m->mnt)) {
+		*err = -EINVAL;
+		goto out;
+	}
+
+	if (!(mnt_has_parent(m) ? check_mnt(m) : is_anon_ns(m->mnt_ns))) {
+		*err = -EINVAL;
+		goto out;
+	}
+
+	do {
+		unsigned int flags;
+
+		flags = recalc_flags(kattr, m);
+		if (!can_change_locked_flags(m, flags)) {
+			*err = -EPERM;
+			goto out;
+		}
+
+		last = m;
+
+		if ((kattr->attr_set & MNT_READONLY) &&
+		    !(m->mnt.mnt_flags & MNT_READONLY)) {
+			*err = mnt_hold_writers(m);
+			if (*err)
+				goto out;
+		}
+	} while (kattr->recurse && (m = next_mnt(m, mnt)));
+
+out:
+	return last;
+}
+
+static void mount_setattr_commit(struct mount_kattr *kattr, struct mount *mnt,
+				 struct mount *last, int err)
+{
+	struct mount *m = mnt;
+
+	do {
+		if (!err) {
+			unsigned int flags;
+
+			flags = recalc_flags(kattr, m);
+			WRITE_ONCE(m->mnt.mnt_flags, flags);
+		}
+
+		/*
+		 * We either set MNT_READONLY above so make it visible
+		 * before ~MNT_WRITE_HOLD or we failed to recursively
+		 * apply mount options.
+		 */
+		if ((kattr->attr_set & MNT_READONLY) &&
+		    (m->mnt.mnt_flags & MNT_WRITE_HOLD))
+			mnt_unhold_writers(m);
+
+		if (!err && kattr->propagation)
+			change_mnt_propagation(m, kattr->propagation);
+
+		/*
+		 * On failure, only cleanup until we found the first mount we
+		 * failed to handle.
+		 */
+		if (err && m == last)
+			break;
+	} while (kattr->recurse && (m = next_mnt(m, mnt)));
+
+	if (!err)
+		touch_mnt_namespace(mnt->mnt_ns);
+}
+
+static int do_mount_setattr(struct path *path, struct mount_kattr *kattr)
+{
+	struct mount *mnt = real_mount(path->mnt), *last = NULL;
+	int err = 0;
+
+	if (path->dentry != mnt->mnt.mnt_root)
+		return -EINVAL;
+
+	if (kattr->propagation) {
+		/*
+		 * Only take namespace_lock() if we're actually changing
+		 * propagation.
+		 */
+		namespace_lock();
+		if (kattr->propagation == MS_SHARED) {
+			err = invent_group_ids(mnt, kattr->recurse);
+			if (err) {
+				namespace_unlock();
+				return err;
+			}
+		}
+	}
+
+	lock_mount_hash();
+
+	/*
+	 * Get the mount tree in a shape where we can change mount properties
+	 * without failure.
+	 */
+	last = mount_setattr_prepare(kattr, mnt, &err);
+	if (last) /* Commit all changes or revert to the old state. */
+		mount_setattr_commit(kattr, mnt, last, err);
+
+	unlock_mount_hash();
+
+	if (kattr->propagation) {
+		namespace_unlock();
+		if (err)
+			cleanup_group_ids(mnt, NULL);
+	}
+
+	return err;
+}
+
+static int build_mount_kattr(const struct mount_attr *attr,
+			     struct mount_kattr *kattr, unsigned int flags)
+{
+	unsigned int lookup_flags = LOOKUP_AUTOMOUNT | LOOKUP_FOLLOW;
+
+	if (flags & AT_NO_AUTOMOUNT)
+		lookup_flags &= ~LOOKUP_AUTOMOUNT;
+	if (flags & AT_SYMLINK_NOFOLLOW)
+		lookup_flags &= ~LOOKUP_FOLLOW;
+	if (flags & AT_EMPTY_PATH)
+		lookup_flags |= LOOKUP_EMPTY;
+
+	*kattr = (struct mount_kattr){
+		.lookup_flags	= lookup_flags,
+		.recurse	= !!(flags & AT_RECURSIVE),
+	};
+
+	switch (attr->propagation) {
+	case MAKE_PROPAGATION_UNCHANGED:
+		kattr->propagation = 0;
+		break;
+	case MAKE_PROPAGATION_UNBINDABLE:
+		kattr->propagation = MS_UNBINDABLE;
+		break;
+	case MAKE_PROPAGATION_PRIVATE:
+		kattr->propagation = MS_PRIVATE;
+		break;
+	case MAKE_PROPAGATION_DEPENDENT:
+		kattr->propagation = MS_SLAVE;
+		break;
+	case MAKE_PROPAGATION_SHARED:
+		kattr->propagation = MS_SHARED;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	if (upper_32_bits(attr->attr_set))
+		return -EINVAL;
+	if (build_attr_flags(lower_32_bits(attr->attr_set), &kattr->attr_set))
+		return -EINVAL;
+
+	if (upper_32_bits(attr->attr_clr))
+		return -EINVAL;
+	if (build_attr_flags(lower_32_bits(attr->attr_clr), &kattr->attr_clr))
+		return -EINVAL;
+
+	/*
+	 * Since the MOUNT_ATTR_<atime> values are an enum, not a bitmap, users
+	 * wanting to transition to a different atime setting cannot simply
+	 * specify the atime setting in @attr_set, but must also specify
+	 * MOUNT_ATTR__ATIME in the @attr_clr field.
+	 * So ensure that MOUNT_ATTR__ATIME can't be partially set in
+	 * @attr_clr and that @attr_set can't have any atime bits set if
+	 * MOUNT_ATTR__ATIME isn't set in @attr_clr.
+	 */
+	if (!(attr->attr_clr & MOUNT_ATTR__ATIME) && (attr->attr_set & MOUNT_ATTR__ATIME))
+		return -EINVAL;
+	else if ((attr->attr_clr & MOUNT_ATTR__ATIME) &&
+		 ((attr->attr_clr & MOUNT_ATTR__ATIME) != MOUNT_ATTR__ATIME))
+		return -EINVAL;
+
+	if (attr->attr_clr & MOUNT_ATTR__ATIME) {
+		/* Clear all previous time settings as they are mutually exclusive. */
+		kattr->attr_clr |= MNT_RELATIME | MNT_NOATIME;
+		switch (attr->attr_set & MOUNT_ATTR__ATIME) {
+		case MOUNT_ATTR_RELATIME:
+			kattr->attr_set |= MNT_RELATIME;
+			break;
+		case MOUNT_ATTR_NOATIME:
+			kattr->attr_set |= MNT_NOATIME;
+			break;
+		case MOUNT_ATTR_STRICTATIME:
+			break;
+		default:
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path, unsigned int, flags,
+		struct mount_attr __user *, uattr, size_t, usize)
+{
+	int err;
+	struct path target;
+	struct mount_attr attr;
+	struct mount_kattr kattr;
+
+	BUILD_BUG_ON(sizeof(struct mount_attr) < MOUNT_ATTR_SIZE_VER0);
+	BUILD_BUG_ON(sizeof(struct mount_attr) != MOUNT_ATTR_SIZE_LATEST);
+
+	if (flags & ~(AT_EMPTY_PATH | AT_RECURSIVE | AT_SYMLINK_NOFOLLOW | AT_NO_AUTOMOUNT))
+		return -EINVAL;
+
+	if (unlikely(usize < MOUNT_ATTR_SIZE_VER0))
+		return -EINVAL;
+
+	if (!may_mount())
+		return -EPERM;
+
+	err = copy_struct_from_user(&attr, sizeof(attr), uattr, usize);
+	if (err)
+		return err;
+
+	if (attr.attr_set == 0 && attr.attr_clr == 0 && attr.propagation == 0)
+		return 0;
+
+	err = build_mount_kattr(&attr, &kattr, flags);
+	if (err)
+		return err;
+
+	err = user_path_at(dfd, path, kattr.lookup_flags, &target);
+	if (err)
+		return err;
+
+	err = do_mount_setattr(&target, &kattr);
+	path_put(&target);
+	return err;
+}
+
 static void __init init_mount_tree(void)
 {
 	struct vfsmount *mnt;
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 37bea07c12f2..a62d5904fb6a 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -68,6 +68,7 @@ union bpf_attr;
 struct io_uring_params;
 struct clone_args;
 struct open_how;
+struct mount_attr;
 
 #include <linux/types.h>
 #include <linux/aio_abi.h>
@@ -999,6 +1000,8 @@ asmlinkage long sys_open_tree(int dfd, const char __user *path, unsigned flags);
 asmlinkage long sys_move_mount(int from_dfd, const char __user *from_path,
 			       int to_dfd, const char __user *to_path,
 			       unsigned int ms_flags);
+asmlinkage long sys_mount_setattr(int dfd, const char __user *path, unsigned int flags,
+				  struct mount_attr __user *uattr, size_t usize);
 asmlinkage long sys_fsopen(const char __user *fs_name, unsigned int flags);
 asmlinkage long sys_fsconfig(int fs_fd, unsigned int cmd, const char __user *key,
 			     const void __user *value, int aux);
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 2056318988f7..0517f36fe783 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -859,9 +859,11 @@ __SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
 __SYSCALL(__NR_faccessat2, sys_faccessat2)
 #define __NR_process_madvise 440
 __SYSCALL(__NR_process_madvise, sys_process_madvise)
+#define __NR_mount_setattr 441
+__SYSCALL(__NR_mount_setattr, sys_mount_setattr)
 
 #undef __NR_syscalls
-#define __NR_syscalls 441
+#define __NR_syscalls 442
 
 /*
  * 32 bit systems traditionally used different
diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h
index dd8306ea336c..fb3ad26fdebf 100644
--- a/include/uapi/linux/mount.h
+++ b/include/uapi/linux/mount.h
@@ -118,4 +118,26 @@ enum fsconfig_command {
 #define MOUNT_ATTR_STRICTATIME	0x00000020 /* - Always perform atime updates */
 #define MOUNT_ATTR_NODIRATIME	0x00000080 /* Do not update directory access times */
 
+/*
+ * mount_setattr()
+ */
+struct mount_attr {
+	__u64 attr_set;
+	__u64 attr_clr;
+	__u64 propagation;
+};
+
+/* Change propagation through mount_setattr(). */
+enum propagation_type {
+	MAKE_PROPAGATION_UNCHANGED	= 0, /* Don't change mount propagation (default). */
+	MAKE_PROPAGATION_UNBINDABLE	= 1, /* Make unbindable. */
+	MAKE_PROPAGATION_PRIVATE	= 2, /* Do not receive or send mount events. */
+	MAKE_PROPAGATION_DEPENDENT	= 3, /* Only receive mount events. */
+	MAKE_PROPAGATION_SHARED		= 4, /* Send and receive mount events. */
+};
+
+/* List of all mount_attr versions. */
+#define MOUNT_ATTR_SIZE_VER0	24 /* sizeof first published struct */
+#define MOUNT_ATTR_SIZE_LATEST	MOUNT_ATTR_SIZE_VER0
+
 #endif /* _UAPI_LINUX_MOUNT_H */
diff --git a/tools/include/uapi/asm-generic/unistd.h b/tools/include/uapi/asm-generic/unistd.h
index f2b5d72a46c2..1cbe8bbda5fa 100644
--- a/tools/include/uapi/asm-generic/unistd.h
+++ b/tools/include/uapi/asm-generic/unistd.h
@@ -857,9 +857,11 @@ __SYSCALL(__NR_openat2, sys_openat2)
 __SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
 #define __NR_faccessat2 439
 __SYSCALL(__NR_faccessat2, sys_faccessat2)
+#define __NR_mount_setattr 441
+__SYSCALL(__NR_mount_setattr, sys_mount_setattr)
 
 #undef __NR_syscalls
-#define __NR_syscalls 440
+#define __NR_syscalls 442
 
 /*
  * 32 bit systems traditionally used different
-- 
2.29.2

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