Re: [PATCH v2 03/10] userns: Add a limit on the number of user namespaces
Quoting Eric W. Biederman (ebied...@xmission.com):
> Export the export the maximum number of user namespaces as
^ note if you resend, duplicate "export the"
> /proc/sys/userns/max_user_namespaces.
>
> Signed-off-by: "Eric W. Biederman"
Acked-by: Serge Hallyn
> ---
> include/linux/user_namespace.h | 2 ++
> kernel/fork.c | 2 ++
> kernel/user_namespace.c| 69
> +-
> 3 files changed, 65 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> index 7d59af1f08f1..ba6a995178f9 100644
> --- a/include/linux/user_namespace.h
> +++ b/include/linux/user_namespace.h
> @@ -43,6 +43,8 @@ struct user_namespace {
> struct ctl_table_setset;
> struct ctl_table_header *sysctls;
> #endif
> + int max_user_namespaces;
> + atomic_t user_namespaces;
> };
>
> extern struct user_namespace init_user_ns;
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 5c2c355aa97f..95d5498c463f 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -323,6 +323,8 @@ void __init fork_init(void)
> init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
> init_task.signal->rlim[RLIMIT_SIGPENDING] =
> init_task.signal->rlim[RLIMIT_NPROC];
> +
> + init_user_ns.max_user_namespaces = max_threads;
> }
>
> int __weak arch_dup_task_struct(struct task_struct *dst,
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 10afbb55dfc2..0061550e3282 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -29,6 +29,7 @@ static DEFINE_MUTEX(userns_state_mutex);
> static bool new_idmap_permitted(const struct file *file,
> struct user_namespace *ns, int cap_setid,
> struct uid_gid_map *map);
> +#define COUNT_MAX (INT_MAX - 1)
>
> #ifdef CONFIG_SYSCTL
> static struct ctl_table_set *
> @@ -63,7 +64,18 @@ static struct ctl_table_root set_root = {
> .permissions = set_permissions,
> };
>
> +static int zero = 0;
> +static int count_max = COUNT_MAX;
> static struct ctl_table userns_table[] = {
> + {
> + .procname = "max_user_namespaces",
> + .data = &init_user_ns.max_user_namespaces,
> + .maxlen = sizeof(init_user_ns.max_user_namespaces),
> + .mode = 0644,
> + .proc_handler = proc_dointvec_minmax,
> + .extra1 = &zero,
> + .extra2 = &count_max,
> + },
> { }
> };
> #endif /* CONFIG_SYSCTL */
> @@ -75,6 +87,8 @@ static bool setup_userns_sysctls(struct user_namespace *ns)
> setup_sysctl_set(&ns->set, &set_root, set_is_seen);
> tbl = kmemdup(userns_table, sizeof(userns_table), GFP_KERNEL);
> if (tbl) {
> + tbl[0].data = &ns->max_user_namespaces;
> +
> ns->sysctls = __register_sysctl_table(&ns->set, "userns", tbl);
> }
> if (!ns->sysctls) {
> @@ -113,6 +127,34 @@ static void set_cred_user_ns(struct cred *cred, struct
> user_namespace *user_ns)
> cred->user_ns = user_ns;
> }
>
> +static bool inc_user_namespaces(struct user_namespace *ns)
> +{
> + struct user_namespace *pos, *bad;
> + for (pos = ns; pos; pos = pos->parent) {
> + int max = READ_ONCE(pos->max_user_namespaces);
> + int sum = atomic_inc_return(&pos->user_namespaces);
> + if (sum > max)
> + goto fail;
> + }
> + return true;
> +fail:
> + bad = pos;
> + atomic_dec(&pos->user_namespaces);
> + for (pos = ns; pos != bad; pos = pos->parent)
> + atomic_dec(&pos->user_namespaces);
> +
> + return false;
> +}
> +
> +static void dec_user_namespaces(struct user_namespace *ns)
> +{
> + struct user_namespace *pos;
> + for (pos = ns; pos; pos = pos->parent) {
> + int dec = atomic_dec_if_positive(&pos->user_namespaces);
> + WARN_ON_ONCE(dec < 0);
> + }
> +}
> +
> /*
> * Create a new user namespace, deriving the creator from the user in the
> * passed credentials, and replacing that user with the new root user for the
> @@ -128,8 +170,12 @@ int create_user_ns(struct cred *new)
> kgid_t group = new->egid;
> int ret;
>
> + ret = -EUSERS;
> if (parent_ns->level > 32)
> - return -EUSERS;
> + goto fail;
> +
> + if (!inc_user_namespaces(parent_ns))
> + goto fail;
>
> /*
>* Verify that we can not violate the policy of which files
> @@ -137,26 +183,27 @@ int create_user_ns(struct cred *new)
>* by verifing that the root directory is at the root of the
>* mount namespace which allows all files to be accessed.
>*/
> + ret = -EPERM;
> if (current_chrooted())
> - return -EPERM;
> + goto fail_dec;
>
> /* The creator needs a mapping in the p
[PATCH v2 03/10] userns: Add a limit on the number of user namespaces
Export the export the maximum number of user namespaces as
/proc/sys/userns/max_user_namespaces.
Signed-off-by: "Eric W. Biederman"
---
include/linux/user_namespace.h | 2 ++
kernel/fork.c | 2 ++
kernel/user_namespace.c| 69 +-
3 files changed, 65 insertions(+), 8 deletions(-)
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 7d59af1f08f1..ba6a995178f9 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -43,6 +43,8 @@ struct user_namespace {
struct ctl_table_setset;
struct ctl_table_header *sysctls;
#endif
+ int max_user_namespaces;
+ atomic_t user_namespaces;
};
extern struct user_namespace init_user_ns;
diff --git a/kernel/fork.c b/kernel/fork.c
index 5c2c355aa97f..95d5498c463f 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -323,6 +323,8 @@ void __init fork_init(void)
init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
init_task.signal->rlim[RLIMIT_SIGPENDING] =
init_task.signal->rlim[RLIMIT_NPROC];
+
+ init_user_ns.max_user_namespaces = max_threads;
}
int __weak arch_dup_task_struct(struct task_struct *dst,
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 10afbb55dfc2..0061550e3282 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -29,6 +29,7 @@ static DEFINE_MUTEX(userns_state_mutex);
static bool new_idmap_permitted(const struct file *file,
struct user_namespace *ns, int cap_setid,
struct uid_gid_map *map);
+#define COUNT_MAX (INT_MAX - 1)
#ifdef CONFIG_SYSCTL
static struct ctl_table_set *
@@ -63,7 +64,18 @@ static struct ctl_table_root set_root = {
.permissions = set_permissions,
};
+static int zero = 0;
+static int count_max = COUNT_MAX;
static struct ctl_table userns_table[] = {
+ {
+ .procname = "max_user_namespaces",
+ .data = &init_user_ns.max_user_namespaces,
+ .maxlen = sizeof(init_user_ns.max_user_namespaces),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &count_max,
+ },
{ }
};
#endif /* CONFIG_SYSCTL */
@@ -75,6 +87,8 @@ static bool setup_userns_sysctls(struct user_namespace *ns)
setup_sysctl_set(&ns->set, &set_root, set_is_seen);
tbl = kmemdup(userns_table, sizeof(userns_table), GFP_KERNEL);
if (tbl) {
+ tbl[0].data = &ns->max_user_namespaces;
+
ns->sysctls = __register_sysctl_table(&ns->set, "userns", tbl);
}
if (!ns->sysctls) {
@@ -113,6 +127,34 @@ static void set_cred_user_ns(struct cred *cred, struct
user_namespace *user_ns)
cred->user_ns = user_ns;
}
+static bool inc_user_namespaces(struct user_namespace *ns)
+{
+ struct user_namespace *pos, *bad;
+ for (pos = ns; pos; pos = pos->parent) {
+ int max = READ_ONCE(pos->max_user_namespaces);
+ int sum = atomic_inc_return(&pos->user_namespaces);
+ if (sum > max)
+ goto fail;
+ }
+ return true;
+fail:
+ bad = pos;
+ atomic_dec(&pos->user_namespaces);
+ for (pos = ns; pos != bad; pos = pos->parent)
+ atomic_dec(&pos->user_namespaces);
+
+ return false;
+}
+
+static void dec_user_namespaces(struct user_namespace *ns)
+{
+ struct user_namespace *pos;
+ for (pos = ns; pos; pos = pos->parent) {
+ int dec = atomic_dec_if_positive(&pos->user_namespaces);
+ WARN_ON_ONCE(dec < 0);
+ }
+}
+
/*
* Create a new user namespace, deriving the creator from the user in the
* passed credentials, and replacing that user with the new root user for the
@@ -128,8 +170,12 @@ int create_user_ns(struct cred *new)
kgid_t group = new->egid;
int ret;
+ ret = -EUSERS;
if (parent_ns->level > 32)
- return -EUSERS;
+ goto fail;
+
+ if (!inc_user_namespaces(parent_ns))
+ goto fail;
/*
* Verify that we can not violate the policy of which files
@@ -137,26 +183,27 @@ int create_user_ns(struct cred *new)
* by verifing that the root directory is at the root of the
* mount namespace which allows all files to be accessed.
*/
+ ret = -EPERM;
if (current_chrooted())
- return -EPERM;
+ goto fail_dec;
/* The creator needs a mapping in the parent user namespace
* or else we won't be able to reasonably tell userspace who
* created a user_namespace.
*/
+ ret = -EPERM;
if (!kuid_has_mapping(parent_ns, owner) ||
!kgid_has_mapping(parent_ns, group))
-
