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Subject[RFC] Make Yama pid_ns aware
Hi,

As Yama's sysctls are about defining a security policy for the system,
it is reasonable to define it per container in case of LXC containers
(or out-of-tree alternatives like OpenVZ). In my opinion they belong
to pid namespace. With per-pid_ns sysctls it is possible to create
multiple containers with different ptrace, /tmp, etc. policies.

As Yama is not merged yet, I post the patch in this thread.

The patch is straightforward:

1) all sysctl variables are moved from global vars to pid_namespace
fields.

2) each cloned pid ns gets the settings of the parent.

3) the variables of current pid ns are visible through sysctl interface.

proc_pid_dointvec_minmax() is stolen from its ipc_ns equivalent in
ipc/ipc_sysctl.c.

(The patch is not tested.)

diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 38d1032..46edaf8 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -30,6 +30,11 @@ struct pid_namespace {
#ifdef CONFIG_BSD_PROCESS_ACCT
struct bsd_acct_struct *bacct;
#endif
+#ifdef CONFIG_SECURITY_YAMA
+ int ptrace_scope;
+ int protected_sticky_symlinks;
+ int protected_nonaccess_hardlinks;
+#endif
};

extern struct pid_namespace init_pid_ns;
diff --git a/kernel/pid.c b/kernel/pid.c
index fa5f722..0cd8926 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -78,6 +78,11 @@ struct pid_namespace init_pid_ns = {
.last_pid = 0,
.level = 0,
.child_reaper = &init_task,
+#ifdef CONFIG_SECURITY_YAMA
+ .ptrace_scope = 1,
+ .protected_sticky_symlinks = 1,
+ .protected_nonaccess_hardlinks = 1,
+#endif
};
EXPORT_SYMBOL_GPL(init_pid_ns);

diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index e9c9adc..73d47c4 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -101,6 +101,14 @@ static struct pid_namespace *create_pid_namespace(struct pid_namespace *parent_p
if (err)
goto out_put_parent_pid_ns;

+#ifdef CONFIG_SECURITY_YAMA
+ ns->ptrace_scope = parent_pid_ns->ptrace_scope;
+ ns->protected_sticky_symlinks =
+ parent_pid_ns->protected_sticky_symlinks;
+ ns->protected_nonaccess_hardlinks =
+ parent_pid_ns->protected_nonaccess_hardlinks;
+#endif
+
return ns;

out_put_parent_pid_ns:
diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index a92538c..cf99a8c 100644
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -16,10 +16,7 @@
#include <linux/ptrace.h>
#include <linux/prctl.h>
#include <linux/ratelimit.h>
-
-static int ptrace_scope = 1;
-static int protected_sticky_symlinks = 1;
-static int protected_nonaccess_hardlinks = 1;
+#include <linux/pid_namespace.h>

/* describe a PTRACE relationship for potential exception */
struct ptrace_relation {
@@ -250,7 +247,7 @@ static int yama_ptrace_access_check(struct task_struct *child,

/* require ptrace target be a child of ptracer on attach */
if (mode == PTRACE_MODE_ATTACH &&
- ptrace_scope &&
+ current->nsproxy->pid_ns->ptrace_scope &&
!capable(CAP_SYS_PTRACE) &&
!task_is_descendant(current, child) &&
!ptracer_exception_found(current, child))
@@ -292,7 +289,7 @@ static int yama_inode_follow_link(struct dentry *dentry,
const struct inode *inode;
const struct cred *cred;

- if (!protected_sticky_symlinks)
+ if (!current->nsproxy->pid_ns->protected_sticky_symlinks)
return 0;

/* if inode isn't a symlink, don't try to evaluate blocking it */
@@ -362,7 +359,7 @@ static int yama_path_link(struct dentry *old_dentry, struct path *new_dir,
const int mode = inode->i_mode;
const struct cred *cred = current_cred();

- if (!protected_nonaccess_hardlinks)
+ if (!current->nsproxy->pid_ns->protected_nonaccess_hardlinks)
return 0;

if (cred->fsuid != inode->i_uid &&
@@ -395,6 +392,26 @@ static struct security_operations yama_ops = {
static int zero;
static int one = 1;

+static void *get_pid_data(ctl_table *table)
+{
+ char *which = table->data;
+ struct pid_namespace *pid_ns = current->nsproxy->pid_ns;
+ which = (which - (char *)&init_pid_ns) + (char *)pid_ns;
+ return which;
+}
+
+static int proc_pid_dointvec_minmax(ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ struct ctl_table pid_table;
+
+ memcpy(&pid_table, table, sizeof(pid_table));
+ pid_table.data = get_pid_data(table);
+
+ return proc_dointvec_minmax(&pid_table, write, buffer, lenp, ppos);
+}
+
+
struct ctl_path yama_sysctl_path[] = {
{ .procname = "kernel", },
{ .procname = "yama", },
@@ -404,28 +421,28 @@ struct ctl_path yama_sysctl_path[] = {
static struct ctl_table yama_sysctl_table[] = {
{
.procname = "protected_sticky_symlinks",
- .data = &protected_sticky_symlinks,
+ .data = &init_pid_ns.protected_sticky_symlinks,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = proc_dointvec_minmax,
+ .proc_handler = proc_pid_dointvec_minmax,
.extra1 = &zero,
.extra2 = &one,
},
{
.procname = "protected_nonaccess_hardlinks",
- .data = &protected_nonaccess_hardlinks,
+ .data = &init_pid_ns.protected_nonaccess_hardlinks,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = proc_dointvec_minmax,
+ .proc_handler = proc_pid_dointvec_minmax,
.extra1 = &zero,
.extra2 = &one,
},
{
.procname = "ptrace_scope",
- .data = &ptrace_scope,
+ .data = &init_pid_ns.ptrace_scope,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = proc_dointvec_minmax,
+ .proc_handler = proc_pid_dointvec_minmax,
.extra1 = &zero,
.extra2 = &one,
},
---

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