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