[PATCH v2 01/28] user_namespace: introduce fsid mappings infrastructure

Christian Brauner
2020-02-14T18:38:52Z

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@ubuntu.com>
---
/* v2 */
- Randy Dunlap <rdunlap@infradead.org>:
- Fix typo in USER_NS_FSID kconfig documentation.
---
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