// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2022 Christian Brauner <brauner@kernel.org> */
#include <linux/cred.h>
#include <linux/fs.h>
#include <linux/mnt_idmapping.h>
#include <linux/slab.h>
#include <linux/user_namespace.h>
#include "internal.h"
struct mnt_idmap {
struct user_namespace *owner;
refcount_t count;
};
/*
* Carries the initial idmapping of 0:0:4294967295 which is an identity
* mapping. This means that {g,u}id 0 is mapped to {g,u}id 0, {g,u}id 1 is
* mapped to {g,u}id 1, [...], {g,u}id 1000 to {g,u}id 1000, [...].
*/
struct mnt_idmap nop_mnt_idmap = {
.owner = &init_user_ns,
.count = REFCOUNT_INIT(1),
};
EXPORT_SYMBOL_GPL(nop_mnt_idmap);
/**
* check_fsmapping - check whether an mount idmapping is allowed
* @idmap: idmap of the relevent mount
* @sb: super block of the filesystem
*
* Return: true if @idmap is allowed, false if not.
*/
bool check_fsmapping(const struct mnt_idmap *idmap,
const struct super_block *sb)
{
return idmap->owner != sb->s_user_ns;
}
/**
* initial_idmapping - check whether this is the initial mapping
* @ns: idmapping to check
*
* Check whether this is the initial mapping, mapping 0 to 0, 1 to 1,
* [...], 1000 to 1000 [...].
*
* Return: true if this is the initial mapping, false if not.
*/
static inline bool initial_idmapping(const struct user_namespace *ns)
{
return ns == &init_user_ns;
}
/**
* no_idmapping - check whether we can skip remapping a kuid/gid
* @mnt_userns: the mount's idmapping
* @fs_userns: the filesystem's idmapping
*
* This function can be used to check whether a remapping between two
* idmappings is required.
* An idmapped mount is a mount that has an idmapping attached to it that
* is different from the filsystem's idmapping and the initial idmapping.
* If the initial mapping is used or the idmapping of the mount and the
* filesystem are identical no remapping is required.
*
* Return: true if remapping can be skipped, false if not.
*/
static inline bool no_idmapping(const struct user_namespace *mnt_userns,
const struct user_namespace *fs_userns)
{
return initial_idmapping(mnt_userns) || mnt_userns == fs_userns;
}
/**
* make_vfsuid - map a filesystem kuid according to an idmapping
* @idmap: the mount's idmapping
* @fs_userns: the filesystem's idmapping
* @kuid : kuid to be mapped
*
* Take a @kuid and remap it from @fs_userns into @idmap. Use this
* function when preparing a @kuid to be reported to userspace.
*
* If no_idmapping() determines that this is not an idmapped mount we can
* simply return @kuid unchanged.
* If initial_idmapping() tells us that the filesystem is not mounted with an
* idmapping we know the value of @kuid won't change when calling
* from_kuid() so we can simply retrieve the value via __kuid_val()
* directly.
*
* Return: @kuid mapped according to @idmap.
* If @kuid has no mapping in either @idmap or @fs_userns INVALID_UID is
* returned.
*/
vfsuid_t make_vfsuid(struct mnt_idmap *idmap,
struct user_namespace *fs_userns,
kuid_t kuid)
{
uid_t uid;
struct user_namespace *mnt_userns = idmap->owner;
if (no_idmapping(mnt_userns, fs_userns))
return VFSUIDT_INIT(kuid);
if (initial_idmapping(fs_userns))
uid = __kuid_val(kuid);
else
uid = from_kuid(fs_userns, kuid);
if (uid == (uid_t)-1)
return INVALID_VFSUID;
return VFSUIDT_INIT(make_kuid(mnt_userns, uid));
}
EXPORT_SYMBOL_GPL(make_vfsuid);
/**
* make_vfsgid - map a filesystem kgid according to an idmapping
* @idmap: the mount's idmapping
* @fs_userns: the filesystem's idmapping
* @kgid : kgid to be mapped
*
* Take a @kgid and remap it from @fs_userns into @idmap. Use this
* function when preparing a @kgid to be reported to userspace.
*
* If no_idmapping() determines that this is not an idmapped mount we can
* simply return @kgid unchanged.
* If initial_idmapping() tells us that the filesystem is not mounted with an
* idmapping we know the value of @kgid won't change when calling
* from_kgid() so we can simply retrieve the value via __kgid_val()
* directly.
*
* Return: @kgid mapped according to @idmap.
* If @kgid has no mapping in either @idmap or @fs_userns INVALID_GID is
* returned.
*/
vfsgid_t make_vfsgid(struct mnt_idmap *idmap,
struct user_namespace *fs_userns, kgid_t kgid)
{
gid_t gid;
struct user_namespace *mnt_userns = idmap->owner;
if (no_idmapping(mnt_userns, fs_userns))
return VFSGIDT_INIT(kgid);
if (initial_idmapping(fs_userns))
gid = __kgid_val(kgid);
else
gid = from_kgid(fs_userns, kgid);
if (gid == (gid_t)-1)
return INVALID_VFSGID;
return VFSGIDT_INIT(make_kgid(mnt_userns, gid));
}
EXPORT_SYMBOL_GPL(make_vfsgid);
/**
* from_vfsuid - map a vfsuid into the filesystem idmapping
* @idmap: the mount's idmapping
* @fs_userns: the filesystem's idmapping
* @vfsuid : vfsuid to be mapped
*
* Map @vfsuid into the filesystem idmapping. This function has to be used in
* order to e.g. write @vfsuid to inode->i_uid.
*
* Return: @vfsuid mapped into the filesystem idmapping
*/
kuid_t from_vfsuid(struct mnt_idmap *idmap,
struct user_namespace *fs_userns, vfsuid_t vfsuid)
{
uid_t uid;
struct user_namespace *mnt_userns = idmap->owner;
if (no_idmapping(mnt_userns, fs_userns))
return AS_KUIDT(vfsuid);
uid = from_kuid(mnt_userns, AS_KUIDT(vfsuid));
if (uid == (uid_t)-1)
return INVALID_UID;
if (initial_idmapping(fs_userns))
return KUIDT_INIT(uid);
return make_kuid(fs_userns, uid);
}
EXPORT_SYMBOL_GPL(from_vfsuid);
/**
* from_vfsgid - map a vfsgid into the filesystem idmapping
* @idmap: the mount's idmapping
* @fs_userns: the filesystem's idmapping
* @vfsgid : vfsgid to be mapped
*
* Map @vfsgid into the filesystem idmapping. This function has to be used in
* order to e.g. write @vfsgid to inode->i_gid.
*
* Return: @vfsgid mapped into the filesystem idmapping
*/
kgid_t from_vfsgid(struct mnt_idmap *idmap,
struct user_namespace *fs_userns, vfsgid_t vfsgid)
{
gid_t gid;
struct user_namespace *mnt_userns = idmap->owner;
if (no_idmapping(mnt_userns, fs_userns))
return AS_KGIDT(vfsgid);
gid = from_kgid(mnt_userns, AS_KGIDT(vfsgid));
if (gid == (gid_t)-1)
return INVALID_GID;
if (initial_idmapping(fs_userns))
return KGIDT_INIT(gid);
return make_kgid(fs_userns, gid);
}
EXPORT_SYMBOL_GPL(from_vfsgid);
#ifdef CONFIG_MULTIUSER
/**
* vfsgid_in_group_p() - check whether a vfsuid matches the caller's groups
* @vfsgid: the mnt gid to match
*
* This function can be used to determine whether @vfsuid matches any of the
* caller's groups.
*
* Return: 1 if vfsuid matches caller's groups, 0 if not.
*/
int vfsgid_in_group_p(vfsgid_t vfsgid)
{
return in_group_p(AS_KGIDT(vfsgid));
}
#else
int vfsgid_in_group_p(vfsgid_t vfsgid)
{
return 1;
}
#endif
EXPORT_SYMBOL_GPL(vfsgid_in_group_p);
struct mnt_idmap *alloc_mnt_idmap(struct user_namespace *mnt_userns)
{
struct mnt_idmap *idmap;
idmap = kzalloc(sizeof(struct mnt_idmap), GFP_KERNEL_ACCOUNT);
if (!idmap)
return ERR_PTR(-ENOMEM);
idmap->owner = get_user_ns(mnt_userns);
refcount_set(&idmap->count, 1);
return idmap;
}
/**
* mnt_idmap_get - get a reference to an idmapping
* @idmap: the idmap to bump the reference on
*
* If @idmap is not the @nop_mnt_idmap bump the reference count.
*
* Return: @idmap with reference count bumped if @not_mnt_idmap isn't passed.
*/
struct mnt_idmap *mnt_idmap_get(struct mnt_idmap *idmap)
{
if (idmap != &nop_mnt_idmap)
refcount_inc(&idmap->count);
return idmap;
}
/**
* mnt_idmap_put - put a reference to an idmapping
* @idmap: the idmap to put the reference on
*
* If this is a non-initial idmapping, put the reference count when a mount is
* released and free it if we're the last user.
*/
void mnt_idmap_put(struct mnt_idmap *idmap)
{
if (idmap != &nop_mnt_idmap && refcount_dec_and_test(&idmap->count)) {
put_user_ns(idmap->owner);
kfree(idmap);
}
}
