Re: [PATCH v3 01/25] user_namespace: introduce fsid mappings infrastructure

From: Serge E. Hallyn
Date: Tue Feb 18 2020 - 21:33:32 EST

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On Tue, Feb 18, 2020 at 03:33:47PM +0100, Christian Brauner wrote:
> This introduces the infrastructure to setup fsid mappings which will be used in
> later patches.
> All new code depends on CONFIG_USER_NS_FSID=y. It currently defaults to "N".
> If CONFIG_USER_NS_FSID is not set, no new code is added.
>
> In this patch fsuid_m_show() and fsgid_m_show() are introduced. They are
> identical to uid_m_show() and gid_m_show() until we introduce from_kfsuid() and
> from_kfsgid() in a follow-up patch.
>
> Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx>

Acked-by: Serge Hallyn <serge@xxxxxxxxxx>

> ---
> /* v2 */
> - Randy Dunlap <rdunlap@xxxxxxxxxxxxx>:
> - Fix typo in USER_NS_FSID kconfig documentation.
>
> /* v3 */
> unchanged
> ---
> include/linux/user_namespace.h | 10 +++
> init/Kconfig | 11 +++
> kernel/user.c | 22 ++++++
> kernel/user_namespace.c | 122 +++++++++++++++++++++++++++++++++
> 4 files changed, 165 insertions(+)
>
> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> index 6ef1c7109fc4..e44742b0cf8a 100644
> --- a/include/linux/user_namespace.h
> +++ b/include/linux/user_namespace.h
> @@ -56,6 +56,10 @@ enum ucount_type {
> struct user_namespace {
> struct uid_gid_map uid_map;
> struct uid_gid_map gid_map;
> +#ifdef CONFIG_USER_NS_FSID
> + struct uid_gid_map fsuid_map;
> + struct uid_gid_map fsgid_map;
> +#endif
> struct uid_gid_map projid_map;
> atomic_t count;
> struct user_namespace *parent;
> @@ -127,6 +131,12 @@ struct seq_operations;
> extern const struct seq_operations proc_uid_seq_operations;
> extern const struct seq_operations proc_gid_seq_operations;
> extern const struct seq_operations proc_projid_seq_operations;
> +#ifdef CONFIG_USER_NS_FSID
> +extern const struct seq_operations proc_fsuid_seq_operations;
> +extern const struct seq_operations proc_fsgid_seq_operations;
> +extern ssize_t proc_fsuid_map_write(struct file *, const char __user *, size_t, loff_t *);
> +extern ssize_t proc_fsgid_map_write(struct file *, const char __user *, size_t, loff_t *);
> +#endif
> extern ssize_t proc_uid_map_write(struct file *, const char __user *, size_t, loff_t *);
> extern ssize_t proc_gid_map_write(struct file *, const char __user *, size_t, loff_t *);
> extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t, loff_t *);
> diff --git a/init/Kconfig b/init/Kconfig
> index cfee56c151f1..d4d0beeba48f 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1111,6 +1111,17 @@ config USER_NS
>
> If unsure, say N.
>
> +config USER_NS_FSID
> + bool "User namespace fsid mappings"
> + depends on USER_NS
> + default n
> + help
> + This allows containers to alter their filesystem id mappings.
> + With this containers with different id mappings can still share
> + the same filesystem.
> +
> + If unsure, say N.
> +
> config PID_NS
> bool "PID Namespaces"
> default y
> diff --git a/kernel/user.c b/kernel/user.c
> index 5235d7f49982..2ccaea9b810b 100644
> --- a/kernel/user.c
> +++ b/kernel/user.c
> @@ -55,6 +55,28 @@ struct user_namespace init_user_ns = {
> },
> },
> },
> +#ifdef CONFIG_USER_NS_FSID
> + .fsuid_map = {
> + .nr_extents = 1,
> + {
> + .extent[0] = {
> + .first = 0,
> + .lower_first = 0,
> + .count = 4294967295U,
> + },
> + },
> + },
> + .fsgid_map = {
> + .nr_extents = 1,
> + {
> + .extent[0] = {
> + .first = 0,
> + .lower_first = 0,
> + .count = 4294967295U,
> + },
> + },
> + },
> +#endif
> .count = ATOMIC_INIT(3),
> .owner = GLOBAL_ROOT_UID,
> .group = GLOBAL_ROOT_GID,
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 8eadadc478f9..cbdf456f95f0 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -191,6 +191,16 @@ static void free_user_ns(struct work_struct *work)
> kfree(ns->projid_map.forward);
> kfree(ns->projid_map.reverse);
> }
> +#ifdef CONFIG_USER_NS_FSID
> + if (ns->fsgid_map.nr_extents > UID_GID_MAP_MAX_BASE_EXTENTS) {
> + kfree(ns->fsgid_map.forward);
> + kfree(ns->fsgid_map.reverse);
> + }
> + if (ns->fsuid_map.nr_extents > UID_GID_MAP_MAX_BASE_EXTENTS) {
> + kfree(ns->fsuid_map.forward);
> + kfree(ns->fsuid_map.reverse);
> + }
> +#endif
> retire_userns_sysctls(ns);
> key_free_user_ns(ns);
> ns_free_inum(&ns->ns);
> @@ -637,6 +647,50 @@ static int projid_m_show(struct seq_file *seq, void *v)
> return 0;
> }
>
> +#ifdef CONFIG_USER_NS_FSID
> +static int fsuid_m_show(struct seq_file *seq, void *v)
> +{
> + struct user_namespace *ns = seq->private;
> + struct uid_gid_extent *extent = v;
> + struct user_namespace *lower_ns;
> + uid_t lower;
> +
> + lower_ns = seq_user_ns(seq);
> + if ((lower_ns == ns) && lower_ns->parent)
> + lower_ns = lower_ns->parent;
> +
> + lower = from_kuid(lower_ns, KUIDT_INIT(extent->lower_first));
> +
> + seq_printf(seq, "%10u %10u %10u\n",
> + extent->first,
> + lower,
> + extent->count);
> +
> + return 0;
> +}
> +
> +static int fsgid_m_show(struct seq_file *seq, void *v)
> +{
> + struct user_namespace *ns = seq->private;
> + struct uid_gid_extent *extent = v;
> + struct user_namespace *lower_ns;
> + gid_t lower;
> +
> + lower_ns = seq_user_ns(seq);
> + if ((lower_ns == ns) && lower_ns->parent)
> + lower_ns = lower_ns->parent;
> +
> + lower = from_kgid(lower_ns, KGIDT_INIT(extent->lower_first));
> +
> + seq_printf(seq, "%10u %10u %10u\n",
> + extent->first,
> + lower,
> + extent->count);
> +
> + return 0;
> +}
> +#endif
> +
> static void *m_start(struct seq_file *seq, loff_t *ppos,
> struct uid_gid_map *map)
> {
> @@ -674,6 +728,22 @@ static void *projid_m_start(struct seq_file *seq, loff_t *ppos)
> return m_start(seq, ppos, &ns->projid_map);
> }
>
> +#ifdef CONFIG_USER_NS_FSID
> +static void *fsuid_m_start(struct seq_file *seq, loff_t *ppos)
> +{
> + struct user_namespace *ns = seq->private;
> +
> + return m_start(seq, ppos, &ns->fsuid_map);
> +}
> +
> +static void *fsgid_m_start(struct seq_file *seq, loff_t *ppos)
> +{
> + struct user_namespace *ns = seq->private;
> +
> + return m_start(seq, ppos, &ns->fsgid_map);
> +}
> +#endif
> +
> static void *m_next(struct seq_file *seq, void *v, loff_t *pos)
> {
> (*pos)++;
> @@ -706,6 +776,22 @@ const struct seq_operations proc_projid_seq_operations = {
> .show = projid_m_show,
> };
>
> +#ifdef CONFIG_USER_NS_FSID
> +const struct seq_operations proc_fsuid_seq_operations = {
> + .start = fsuid_m_start,
> + .stop = m_stop,
> + .next = m_next,
> + .show = fsuid_m_show,
> +};
> +
> +const struct seq_operations proc_fsgid_seq_operations = {
> + .start = fsgid_m_start,
> + .stop = m_stop,
> + .next = m_next,
> + .show = fsgid_m_show,
> +};
> +#endif
> +
> static bool mappings_overlap(struct uid_gid_map *new_map,
> struct uid_gid_extent *extent)
> {
> @@ -1081,6 +1167,42 @@ ssize_t proc_projid_map_write(struct file *file, const char __user *buf,
> &ns->projid_map, &ns->parent->projid_map);
> }
>
> +#ifdef CONFIG_USER_NS_FSID
> +ssize_t proc_fsuid_map_write(struct file *file, const char __user *buf,
> + size_t size, loff_t *ppos)
> +{
> + struct seq_file *seq = file->private_data;
> + struct user_namespace *ns = seq->private;
> + struct user_namespace *seq_ns = seq_user_ns(seq);
> +
> + if (!ns->parent)
> + return -EPERM;
> +
> + if ((seq_ns != ns) && (seq_ns != ns->parent))
> + return -EPERM;
> +
> + return map_write(file, buf, size, ppos, CAP_SETUID, &ns->fsuid_map,
> + &ns->parent->fsuid_map);
> +}
> +
> +ssize_t proc_fsgid_map_write(struct file *file, const char __user *buf,
> + size_t size, loff_t *ppos)
> +{
> + struct seq_file *seq = file->private_data;
> + struct user_namespace *ns = seq->private;
> + struct user_namespace *seq_ns = seq_user_ns(seq);
> +
> + if (!ns->parent)
> + return -EPERM;
> +
> + if ((seq_ns != ns) && (seq_ns != ns->parent))
> + return -EPERM;
> +
> + return map_write(file, buf, size, ppos, CAP_SETGID, &ns->fsgid_map,
> + &ns->parent->fsgid_map);
> +}
> +#endif
> +
> static bool new_idmap_permitted(const struct file *file,
> struct user_namespace *ns, int cap_setid,
> struct uid_gid_map *new_map)
> --
> 2.25.0

Next message: Serge E. Hallyn: "Re: [PATCH v3 02/25] proc: add /proc/<pid>/fsuid_map"
Previous message: David Rientjes: "[patch 2/2] mm, thp: track fallbacks due to failed memcg charges separately"
In reply to: Christian Brauner: "[PATCH v3 01/25] user_namespace: introduce fsid mappings infrastructure"
Next in thread: Christian Brauner: "[PATCH v3 12/25] capability: privileged_wrt_inode_uidgid(): handle fsid mappings"
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