// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2022 Christian Brauner <[email protected]> */
#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"
/*
* Outside of this file vfs{g,u}id_t are always created from k{g,u}id_t,
* never from raw values. These are just internal helpers.
*/
#define VFSUIDT_INIT_RAW(val) (vfsuid_t){ val }
#define VFSGIDT_INIT_RAW(val) (vfsgid_t){ val }
struct mnt_idmap {
struct uid_gid_map uid_map;
struct uid_gid_map gid_map;
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 = {
.count = REFCOUNT_INIT(1),
};
EXPORT_SYMBOL_GPL(nop_mnt_idmap);
/*
* Carries the invalid idmapping of a full 0-4294967295 {g,u}id range.
* This means that all {g,u}ids are mapped to INVALID_VFS{G,U}ID.
*/
struct mnt_idmap invalid_mnt_idmap = {
.count = REFCOUNT_INIT(1),
};
EXPORT_SYMBOL_GPL(invalid_mnt_idmap);
/**
* 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;
}
/**
* 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 initial_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;
if (idmap == &nop_mnt_idmap)
return VFSUIDT_INIT(kuid);
if (idmap == &invalid_mnt_idmap)
return INVALID_VFSUID;
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_RAW(map_id_down(&idmap->uid_map, 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 initial_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;
if (idmap == &nop_mnt_idmap)
return VFSGIDT_INIT(kgid);
if (idmap == &invalid_mnt_idmap)
return INVALID_VFSGID;
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_RAW(map_id_down(&idmap->gid_map, 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;
if (idmap == &nop_mnt_idmap)
return AS_KUIDT(vfsuid);
if (idmap == &invalid_mnt_idmap)
return INVALID_UID;
uid = map_id_up(&idmap->uid_map, __vfsuid_val(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;
if (idmap == &nop_mnt_idmap)
return AS_KGIDT(vfsgid);
if (idmap == &invalid_mnt_idmap)
return INVALID_GID;
gid = map_id_up(&idmap->gid_map, __vfsgid_val(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);
static int copy_mnt_idmap(struct uid_gid_map *map_from,
struct uid_gid_map *map_to)
{
struct uid_gid_extent *forward, *reverse;
u32 nr_extents = READ_ONCE(map_from->nr_extents);
/* Pairs with smp_wmb() when writing the idmapping. */
smp_rmb();
/*
* Don't blindly copy @map_to into @map_from if nr_extents is
* smaller or equal to UID_GID_MAP_MAX_BASE_EXTENTS. Since we
* read @nr_extents someone could have written an idmapping and
* then we might end up with inconsistent data. So just don't do
* anything at all.
*/
if (nr_extents == 0)
return -EINVAL;
/*
* Here we know that nr_extents is greater than zero which means
* a map has been written. Since idmappings can't be changed
* once they have been written we know that we can safely copy
* from @map_to into @map_from.
*/
if (nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS) {
*map_to = *map_from;
return 0;
}
forward = kmemdup_array(map_from->forward, nr_extents,
sizeof(struct uid_gid_extent),
GFP_KERNEL_ACCOUNT);
if (!forward)
return -ENOMEM;
reverse = kmemdup_array(map_from->reverse, nr_extents,
sizeof(struct uid_gid_extent),
GFP_KERNEL_ACCOUNT);
if (!reverse) {
kfree(forward);
return -ENOMEM;
}
/*
* The idmapping isn't exposed anywhere so we don't need to care
* about ordering between extent pointers and @nr_extents
* initialization.
*/
map_to->forward = forward;
map_to->reverse = reverse;
map_to->nr_extents = nr_extents;
return 0;
}
static void free_mnt_idmap(struct mnt_idmap *idmap)
{
if (idmap->uid_map.nr_extents > UID_GID_MAP_MAX_BASE_EXTENTS) {
kfree(idmap->uid_map.forward);
kfree(idmap->uid_map.reverse);
}
if (idmap->gid_map.nr_extents > UID_GID_MAP_MAX_BASE_EXTENTS) {
kfree(idmap->gid_map.forward);
kfree(idmap->gid_map.reverse);
}
kfree(idmap);
}
struct mnt_idmap *alloc_mnt_idmap(struct user_namespace *mnt_userns)
{
struct mnt_idmap *idmap;
int ret;
idmap = kzalloc(sizeof(struct mnt_idmap), GFP_KERNEL_ACCOUNT);
if (!idmap)
return ERR_PTR(-ENOMEM);
refcount_set(&idmap->count, 1);
ret = copy_mnt_idmap(&mnt_userns->uid_map, &idmap->uid_map);
if (!ret)
ret = copy_mnt_idmap(&mnt_userns->gid_map, &idmap->gid_map);
if (ret) {
free_mnt_idmap(idmap);
idmap = ERR_PTR(ret);
}
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 && idmap != &invalid_mnt_idmap)
refcount_inc(&idmap->count);
return idmap;
}
EXPORT_SYMBOL_GPL(mnt_idmap_get);
/**
* 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 && idmap != &invalid_mnt_idmap &&
refcount_dec_and_test(&idmap->count))
free_mnt_idmap(idmap);
}
EXPORT_SYMBOL_GPL(mnt_idmap_put);
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