Pull LSM updates from Paul Moore:
"We only have five patches in the LSM tree, but three of the five are
for an important bugfix relating to overlayfs and the mmap() and
mprotect() access controls for LSMs. Highlights below:
- Fix problems with the mmap() and mprotect() LSM hooks on overlayfs
As we are dealing with problems both in mmap() and mprotect() there
are essentially two components to this fix, spread across three
patches with all marked for stable.
The simplest portion of the fix is the creation of a new LSM hook,
security_mmap_backing_file(), that is used to enforce LSM mmap()
access controls on backing files in the stacked/overlayfs case. The
existing security_mmap_file() does not have visibility past the
user file. You can see from the associated SELinux hook callback
the code is fairly straightforward.
The mprotect() fix is a bit more complicated as there is no way in
the mprotect() code path to inspect both the user and backing
files, and bolting on a second file reference to vm_area_struct
wasn't really an option.
The solution taken here adds a LSM security blob and associated
hooks to the backing_file struct that LSMs can use to capture and
store relevant information from the user file. While the necessary
SELinux information is relatively small, a single u32, I expect
other LSMs to require more than that, and a dedicated backing_file
LSM blob provides a storage mechanism without negatively impacting
other filesystems.
I want to note that other LSMs beyond SELinux have been involved in
the discussion of the fixes presented here and they are working on
their own related changes using these new hooks, but due to other
issues those patches will be coming at a later date.
- Use kstrdup_const()/kfree_const() for securityfs symlink targets
- Resolve a handful of kernel-doc warnings in cred.h"
* tag 'lsm-pr-20260410' of git://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/lsm:
selinux: fix overlayfs mmap() and mprotect() access checks
lsm: add backing_file LSM hooks
fs: prepare for adding LSM blob to backing_file
securityfs: use kstrdup_const() to manage symlink targets
cred: fix kernel-doc warnings in cred.h
Stacked filesystems such as overlayfs do not currently provide the
necessary mechanisms for LSMs to properly enforce access controls on the
mmap() and mprotect() operations. In order to resolve this gap, a LSM
security blob is being added to the backing_file struct and the following
new LSM hooks are being created:
security_backing_file_alloc()
security_backing_file_free()
security_mmap_backing_file()
The first two hooks are to manage the lifecycle of the LSM security blob
in the backing_file struct, while the third provides a new mmap() access
control point for the underlying backing file. It is also expected that
LSMs will likely want to update their security_file_mprotect() callback
to address issues with their mprotect() controls, but that does not
require a change to the security_file_mprotect() LSM hook.
There are a three other small changes to support these new LSM hooks:
* Pass the user file associated with a backing file down to
alloc_empty_backing_file() so it can be included in the
security_backing_file_alloc() hook.
* Add getter and setter functions for the backing_file struct LSM blob
as the backing_file struct remains private to fs/file_table.c.
* Constify the file struct field in the LSM common_audit_data struct to
better support LSMs that need to pass a const file struct pointer into
the common LSM audit code.
Thanks to Arnd Bergmann for identifying the missing EXPORT_SYMBOL_GPL()
and supplying a fixup.
Cc: stable@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-unionfs@vger.kernel.org
Cc: linux-erofs@lists.ozlabs.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Paul Moore <paul@paul-moore.com>
The "small" argument to do_sys_ftruncate indicates if > 32-bit size
should be reject, but all the arch-specific compat ftruncate64
implementations get this wrong. Merge do_sys_ftruncate and
ksys_ftruncate, replace the integer as boolean small flag with a
descriptive one about LFS semantics, and use it correctly in the
architecture-specific ftruncate64 implementations.
Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Fixes: 3dd681d944 ("arm64: 32-bit (compat) applications support")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260323070205.2939118-2-hch@lst.de
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Pull vfs 'struct filename' updates from Al Viro:
"[Mostly] sanitize struct filename handling"
* tag 'pull-filename' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (68 commits)
sysfs(2): fs_index() argument is _not_ a pathname
alpha: switch osf_mount() to strndup_user()
ksmbd: use CLASS(filename_kernel)
mqueue: switch to CLASS(filename)
user_statfs(): switch to CLASS(filename)
statx: switch to CLASS(filename_maybe_null)
quotactl_block(): switch to CLASS(filename)
chroot(2): switch to CLASS(filename)
move_mount(2): switch to CLASS(filename_maybe_null)
namei.c: switch user pathname imports to CLASS(filename{,_flags})
namei.c: convert getname_kernel() callers to CLASS(filename_kernel)
do_f{chmod,chown,access}at(): use CLASS(filename_uflags)
do_readlinkat(): switch to CLASS(filename_flags)
do_sys_truncate(): switch to CLASS(filename)
do_utimes_path(): switch to CLASS(filename_uflags)
chdir(2): unspaghettify a bit...
do_fchownat(): unspaghettify a bit...
fspick(2): use CLASS(filename_flags)
name_to_handle_at(): use CLASS(filename_uflags)
vfs_open_tree(): use CLASS(filename_uflags)
...
Pull vfs mount updates from Christian Brauner:
- statmount: accept fd as a parameter
Extend struct mnt_id_req with a file descriptor field and a new
STATMOUNT_BY_FD flag. When set, statmount() returns mount information
for the mount the fd resides on — including detached mounts
(unmounted via umount2(MNT_DETACH)).
For detached mounts the STATMOUNT_MNT_POINT and STATMOUNT_MNT_NS_ID
mask bits are cleared since neither is meaningful. The capability
check is skipped for STATMOUNT_BY_FD since holding an fd already
implies prior access to the mount and equivalent information is
available through fstatfs() and /proc/pid/mountinfo without
privilege. Includes comprehensive selftests covering both attached
and detached mount cases.
- fs: Remove internal old mount API code (1 patch)
Now that every in-tree filesystem has been converted to the new
mount API, remove all the legacy shim code in fs_context.c that
handled unconverted filesystems. This deletes ~280 lines including
legacy_init_fs_context(), the legacy_fs_context struct, and
associated wrappers. The mount(2) syscall path for userspace remains
untouched. Documentation references to the legacy callbacks are
cleaned up.
- mount: add OPEN_TREE_NAMESPACE to open_tree()
Container runtimes currently use CLONE_NEWNS to copy the caller's
entire mount namespace — only to then pivot_root() and recursively
unmount everything they just copied. With large mount tables and
thousands of parallel container launches this creates significant
contention on the namespace semaphore.
OPEN_TREE_NAMESPACE copies only the specified mount tree (like
OPEN_TREE_CLONE) but returns a mount namespace fd instead of a
detached mount fd. The new namespace contains the copied tree mounted
on top of a clone of the real rootfs.
This functions as a combined unshare(CLONE_NEWNS) + pivot_root() in a
single syscall. Works with user namespaces: an unshare(CLONE_NEWUSER)
followed by OPEN_TREE_NAMESPACE creates a mount namespace owned by
the new user namespace. Mount namespace file mounts are excluded from
the copy to prevent cycles. Includes ~1000 lines of selftests"
* tag 'vfs-7.0-rc1.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
selftests/open_tree: add OPEN_TREE_NAMESPACE tests
mount: add OPEN_TREE_NAMESPACE
fs: Remove internal old mount API code
selftests: statmount: tests for STATMOUNT_BY_FD
statmount: accept fd as a parameter
statmount: permission check should return EPERM
Pull vfs nullfs update from Christian Brauner:
"Add a completely catatonic minimal pseudo filesystem called "nullfs"
and make pivot_root() work in the initramfs.
Currently pivot_root() does not work on the real rootfs because it
cannot be unmounted. Userspace has to recursively delete initramfs
contents manually before continuing boot, using the fragile
switch_root sequence (overmount + chroot).
Add nullfs, a minimal immutable filesystem that serves as the true
root of the mount hierarchy. The mutable rootfs (tmpfs/ramfs) is
mounted on top of it. This allows userspace to simply:
chdir(new_root);
pivot_root(".", ".");
umount2(".", MNT_DETACH);
without the traditional switch_root workarounds. systemd already
handles this correctly. It tries pivot_root() first and falls back
to MS_MOVE only when that fails.
This also means rootfs mounts in unprivileged namespaces no longer
need MNT_LOCKED, since the immutable nullfs guarantees nothing can be
revealed by unmounting the covering mount.
nullfs is a single-instance filesystem (get_tree_single()) marked
SB_NOUSER | SB_I_NOEXEC | SB_I_NODEV with an immutable empty root
directory. This means sooner or later it can be used to overmount
other directories to hide their contents without any additional
protection needed.
We enable it unconditionally. If we see any real regression we'll
hide it behind a boot option.
nullfs has extensions beyond this in the future. It will serve as a
concept to support the creation of completely empty mount namespaces -
which is work coming up in the next cycle"
* tag 'vfs-7.0-rc1.nullfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
fs: use nullfs unconditionally as the real rootfs
docs: mention nullfs
fs: add immutable rootfs
fs: add init_pivot_root()
fs: ensure that internal tmpfs mount gets mount id zero
When creating containers the setup usually involves using CLONE_NEWNS
via clone3() or unshare(). This copies the caller's complete mount
namespace. The runtime will also assemble a new rootfs and then use
pivot_root() to switch the old mount tree with the new rootfs. Afterward
it will recursively umount the old mount tree thereby getting rid of all
mounts.
On a basic system here where the mount table isn't particularly large
this still copies about 30 mounts. Copying all of these mounts only to
get rid of them later is pretty wasteful.
This is exacerbated if intermediary mount namespaces are used that only
exist for a very short amount of time and are immediately destroyed
again causing a ton of mounts to be copied and destroyed needlessly.
With a large mount table and a system where thousands or ten-thousands
of containers are spawned in parallel this quickly becomes a bottleneck
increasing contention on the semaphore.
Extend open_tree() with a new OPEN_TREE_NAMESPACE flag. Similar to
OPEN_TREE_CLONE only the indicated mount tree is copied. Instead of
returning a file descriptor referring to that mount tree
OPEN_TREE_NAMESPACE will cause open_tree() to return a file descriptor
to a new mount namespace. In that new mount namespace the copied mount
tree has been mounted on top of a copy of the real rootfs.
The caller can setns() into that mount namespace and perform any
additionally required setup such as move_mount() detached mounts in
there.
This allows OPEN_TREE_NAMESPACE to function as a combined
unshare(CLONE_NEWNS) and pivot_root().
A caller may for example choose to create an extremely minimal rootfs:
fd_mntns = open_tree(-EBADF, "/var/lib/containers/wootwoot", OPEN_TREE_NAMESPACE);
This will create a mount namespace where "wootwoot" has become the
rootfs mounted on top of the real rootfs. The caller can now setns()
into this new mount namespace and assemble additional mounts.
This also works with user namespaces:
unshare(CLONE_NEWUSER);
fd_mntns = open_tree(-EBADF, "/var/lib/containers/wootwoot", OPEN_TREE_NAMESPACE);
which creates a new mount namespace owned by the earlier created user
namespace with "wootwoot" as the rootfs mounted on top of the real
rootfs.
Link: https://patch.msgid.link/20251229-work-empty-namespace-v1-1-bfb24c7b061f@kernel.org
Tested-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Aleksa Sarai <cyphar@cyphar.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Suggested-by: Christian Brauner <brauner@kernel.org>
Suggested-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
filename_renameat2() replaces do_renameat2(); unlike the latter,
it does not drop filename references - these days it can be just
as easily arranged in the caller.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
"filp" thing never made sense; seeing that there are exactly 4 callers
in the entire tree (and it's neither exported nor even declared in
linux/*/*.h), there's no point keeping that ugliness.
FWIW, the 'filp' thing did originate in OSD&I; for some reason Tanenbaum
decided to call the object representing an opened file 'struct filp',
the last letter standing for 'position'. In all Unices, Linux included,
the corresponding object had always been 'struct file'...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Instances of struct filename come from names_cachep (via
__getname()). That is done by getname_flags() and getname_kernel()
and these two are the main callers of __getname(). However, there are
other callers that simply want to allocate PATH_MAX bytes for uses that
have nothing to do with struct filename.
We want saner allocation rules for long pathnames, so that struct
filename would *always* come from names_cachep, with the out-of-line
pathname getting kmalloc'ed. For that we need to be able to change the
size of objects allocated by getname_flags()/getname_kernel().
That requires the rest of __getname() users to stop using
names_cachep; we could explicitly switch all of those to kmalloc(),
but that would cause quite a bit of noise. So the plan is to switch
getname_...() to new helpers and turn __getname() into a wrapper for
kmalloc(). Remaining __getname() users could be converted to explicit
kmalloc() at leisure, hopefully along with figuring out what size do
they really want - PATH_MAX is an overkill for some of them, used out
of laziness ("we have a convenient helper that does 4K allocations and
that's large enough, let's use it").
As a side benefit, names_cachep is no longer used outside
of fs/namei.c, so we can move it there and be done with that.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Now that the last in-tree filesystem has been converted to the new mount
API, remove all legacy mount API code designed to handle un-converted
filesystems, and remove associated documentation as well.
(The code to handle the legacy mount(2) syscall from userspace is still
in place, of course.)
Tested with an allmodconfig build on x86_64, and a sanity check of an
old mount(2) syscall mount.
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Link: https://patch.msgid.link/20251212174403.2882183-1-sandeen@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Pull persistent dentry infrastructure and conversion from Al Viro:
"Some filesystems use a kinda-sorta controlled dentry refcount leak to
pin dentries of created objects in dcache (and undo it when removing
those). A reference is grabbed and not released, but it's not actually
_stored_ anywhere.
That works, but it's hard to follow and verify; among other things, we
have no way to tell _which_ of the increments is intended to be an
unpaired one. Worse, on removal we need to decide whether the
reference had already been dropped, which can be non-trivial if that
removal is on umount and we need to figure out if this dentry is
pinned due to e.g. unlink() not done. Usually that is handled by using
kill_litter_super() as ->kill_sb(), but there are open-coded special
cases of the same (consider e.g. /proc/self).
Things get simpler if we introduce a new dentry flag
(DCACHE_PERSISTENT) marking those "leaked" dentries. Having it set
claims responsibility for +1 in refcount.
The end result this series is aiming for:
- get these unbalanced dget() and dput() replaced with new primitives
that would, in addition to adjusting refcount, set and clear
persistency flag.
- instead of having kill_litter_super() mess with removing the
remaining "leaked" references (e.g. for all tmpfs files that hadn't
been removed prior to umount), have the regular
shrink_dcache_for_umount() strip DCACHE_PERSISTENT of all dentries,
dropping the corresponding reference if it had been set. After that
kill_litter_super() becomes an equivalent of kill_anon_super().
Doing that in a single step is not feasible - it would affect too many
places in too many filesystems. It has to be split into a series.
This work has really started early in 2024; quite a few preliminary
pieces have already gone into mainline. This chunk is finally getting
to the meat of that stuff - infrastructure and most of the conversions
to it.
Some pieces are still sitting in the local branches, but the bulk of
that stuff is here"
* tag 'pull-persistency' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (54 commits)
d_make_discardable(): warn if given a non-persistent dentry
kill securityfs_recursive_remove()
convert securityfs
get rid of kill_litter_super()
convert rust_binderfs
convert nfsctl
convert rpc_pipefs
convert hypfs
hypfs: swich hypfs_create_u64() to returning int
hypfs: switch hypfs_create_str() to returning int
hypfs: don't pin dentries twice
convert gadgetfs
gadgetfs: switch to simple_remove_by_name()
convert functionfs
functionfs: switch to simple_remove_by_name()
functionfs: fix the open/removal races
functionfs: need to cancel ->reset_work in ->kill_sb()
functionfs: don't bother with ffs->ref in ffs_data_{opened,closed}()
functionfs: don't abuse ffs_data_closed() on fs shutdown
convert selinuxfs
...
The fact that directory operations (create,remove,rename) are protected
by a lock on the parent is known widely throughout the kernel.
In order to change this - to instead lock the target dentry - it is
best to centralise this knowledge so it can be changed in one place.
This patch introduces start_dirop() which is local to VFS code.
It performs the required locking for create and remove. Rename
will be handled separately.
Various functions with names like start_creating() or start_removing_path(),
some of which already exist, will export this functionality beyond the VFS.
end_dirop() is the partner of start_dirop(). It drops the lock and
releases the reference on the dentry.
It *is* exported so that various end_creating etc functions can be inline.
As vfs_mkdir() drops the dentry on error we cannot use end_dirop() as
that won't unlock when the dentry IS_ERR(). For now we need an explicit
unlock when dentry IS_ERR(). I hope to change vfs_mkdir() to unlock
when it drops a dentry so that explicit unlock can go away.
end_dirop() can always be called on the result of start_dirop(), but not
after vfs_mkdir(). After a vfs_mkdir() we still may need the explicit
unlock as seen in end_creating_path().
As well as adding start_dirop() and end_dirop()
this patch uses them in:
- simple_start_creating (which requires sharing lookup_noperm_common()
with libfs.c)
- start_removing_path / start_removing_user_path_at
- filename_create / end_creating_path()
- do_rmdir(), do_unlinkat()
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: NeilBrown <neil@brown.name>
Link: https://patch.msgid.link/20251113002050.676694-3-neilb@ownmail.net
Tested-by: syzbot@syzkaller.appspotmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Pull file->f_path constification from Al Viro:
"Only one thing was modifying ->f_path of an opened file - acct(2).
Massaging that away and constifying a bunch of struct path * arguments
in functions that might be given &file->f_path ends up with the
situation where we can turn ->f_path into an anon union of const
struct path f_path and struct path __f_path, the latter modified only
in a few places in fs/{file_table,open,namei}.c, all for struct file
instances that are yet to be opened"
* tag 'pull-f_path' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (23 commits)
Have cc(1) catch attempts to modify ->f_path
kernel/acct.c: saner struct file treatment
configfs:get_target() - release path as soon as we grab configfs_item reference
apparmor/af_unix: constify struct path * arguments
ovl_is_real_file: constify realpath argument
ovl_sync_file(): constify path argument
ovl_lower_dir(): constify path argument
ovl_get_verity_digest(): constify path argument
ovl_validate_verity(): constify {meta,data}path arguments
ovl_ensure_verity_loaded(): constify datapath argument
ksmbd_vfs_set_init_posix_acl(): constify path argument
ksmbd_vfs_inherit_posix_acl(): constify path argument
ksmbd_vfs_kern_path_unlock(): constify path argument
ksmbd_vfs_path_lookup_locked(): root_share_path can be const struct path *
check_export(): constify path argument
export_operations->open(): constify path argument
rqst_exp_get_by_name(): constify path argument
nfs: constify path argument of __vfs_getattr()
bpf...d_path(): constify path argument
done_path_create(): constify path argument
...
Pull vfs mount updates from Al Viro:
"Several piles this cycle, this mount-related one being the largest and
trickiest:
- saner handling of guards in fs/namespace.c, getting rid of
needlessly strong locking in some of the users
- lock_mount() calling conventions change - have it set the
environment for attaching to given location, storing the results in
caller-supplied object, without altering the passed struct path.
Make unlock_mount() called as __cleanup for those objects. It's not
exactly guard(), but similar to it
- MNT_WRITE_HOLD done right.
mnt_hold_writers() does *not* mess with ->mnt_flags anymore, so
insertion of a new mount into ->s_mounts of underlying superblock
does not, in itself, expose ->mnt_flags of that mount to concurrent
modifications
- getting rid of pathological cases when umount() spends quadratic
time removing the victims from propagation graph - part of that had
been dealt with last cycle, this should finish it
- a bunch of stuff constified
- assorted cleanups
* tag 'pull-mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (64 commits)
constify {__,}mnt_is_readonly()
WRITE_HOLD machinery: no need for to bump mount_lock seqcount
struct mount: relocate MNT_WRITE_HOLD bit
preparations to taking MNT_WRITE_HOLD out of ->mnt_flags
setup_mnt(): primitive for connecting a mount to filesystem
simplify the callers of mnt_unhold_writers()
copy_mnt_ns(): use guards
copy_mnt_ns(): use the regular mechanism for freeing empty mnt_ns on failure
open_detached_copy(): separate creation of namespace into helper
open_detached_copy(): don't bother with mount_lock_hash()
path_has_submounts(): use guard(mount_locked_reader)
fs/namespace.c: sanitize descriptions for {__,}lookup_mnt()
ecryptfs: get rid of pointless mount references in ecryptfs dentries
umount_tree(): take all victims out of propagation graph at once
do_mount(): use __free(path_put)
do_move_mount_old(): use __free(path_put)
constify can_move_mount_beneath() arguments
path_umount(): constify struct path argument
may_copy_tree(), __do_loopback(): constify struct path argument
path_mount(): constify struct path argument
...
Linus Torvalds
Paul Moore
Christoph HellwigandChristian Brauner
Al Viro
Eric SandeenandChristian Brauner
NeilBrownandChristian Brauner