[RFC PATCH 5/8] KEYS: exec request-key within the requesting task's init namespace

[Ian Kent <ikent@redhat.com>]

Containerized request key helper callbacks need the ability to execute
a binary in a container's context. To do this calling an in kernel
equivalent of setns(2) should be sufficient since the user mode helper
execution kernel thread ultimately calls do_execve().

Signed-off-by: Ian Kent <ikent@redhat.com>
Cc: Benjamin Coddington <bcodding@redhat.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: J. Bruce Fields <bfields@fieldses.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Trond Myklebust <trond.myklebust@primarydata.com>
Cc: Oleg Nesterov <onestero@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Jeff Layton <jeff.layton@primarydata.com>
---
 security/keys/request_key.c |   60 +++++++++++++++++++++++++++++++++++++------
 1 file changed, 52 insertions(+), 8 deletions(-)

diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 9e79bbf..59282aa 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -17,6 +17,9 @@
 #include <linux/err.h>
 #include <linux/keyctl.h>
 #include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/nsproxy.h>
+#include <net/net_namespace.h>
 #include "internal.h"
 
 #define key_negative_timeout	60	/* default timeout on a negative key's existence */
@@ -46,6 +49,11 @@ void complete_request_key(struct key_construction *cons, int error)
 }
 EXPORT_SYMBOL(complete_request_key);
 
+struct request_key_info {
+	struct key	   *keyring;
+	struct task_struct *tsk;
+};
+
 /*
  * Initialise a usermode helper that is going to have a specific session
  * keyring.
@@ -55,9 +63,18 @@ EXPORT_SYMBOL(complete_request_key);
  */
 static int umh_keys_init(struct subprocess_info *info, struct cred *cred)
 {
-	struct key *keyring = info->data;
+	struct request_key_info *rki = info->data;
+	struct task_struct *tsk = rki->tsk;
+
+	if (tsk) {
+		int err;
+
+		err = umh_enter_ns(tsk, cred);
+		if (err)
+			return err;
+	}
 
-	return install_session_keyring_to_cred(cred, keyring);
+	return install_session_keyring_to_cred(cred, rki->keyring);
 }
 
 /*
@@ -65,8 +82,11 @@ static int umh_keys_init(struct subprocess_info *info, struct cred *cred)
  */
 static void umh_keys_cleanup(struct subprocess_info *info)
 {
-	struct key *keyring = info->data;
-	key_put(keyring);
+	struct request_key_info *rki = info->data;
+	if (rki->tsk)
+		put_task_struct(rki->tsk);
+	key_put(rki->keyring);
+	kfree(rki);
 }
 
 /*
@@ -76,12 +96,32 @@ static int call_usermodehelper_keys(char *path, char **argv, char **envp,
 					struct key *session_keyring, int flags)
 {
 	struct subprocess_info *info;
+	struct request_key_info *rki;
+	unsigned int use_ns = flags & UMH_USE_NS;
+	struct task_struct *tsk = NULL;
+
+	rki = kmalloc(sizeof(*rki), GFP_KERNEL);
+	if (!rki)
+		return -ENOMEM;
+
+	if (use_ns) {
+		tsk = umh_get_init_pid();
+		if (IS_ERR(tsk))
+			return PTR_ERR(tsk);
+	}
+
+	rki->keyring = session_keyring;
+	rki->tsk = tsk;
 
 	info = call_usermodehelper_setup(path, argv, envp, GFP_KERNEL,
 					  umh_keys_init, umh_keys_cleanup,
-					  session_keyring);
-	if (!info)
+					  rki);
+	if (!info) {
+		if (tsk)
+			put_task_struct(rki->tsk);
+		kfree(rki);
 		return -ENOMEM;
+	}
 
 	key_get(session_keyring);
 	return call_usermodehelper_exec(info, flags);
@@ -102,10 +142,15 @@ static int call_sbin_request_key(struct key_construction *cons,
 	char *argv[9], *envp[3], uid_str[12], gid_str[12];
 	char key_str[12], keyring_str[3][12];
 	char desc[20];
+	int flags = UMH_WAIT_PROC;
 	int ret, i;
 
 	kenter("{%d},{%d},%s", key->serial, authkey->serial, op);
 
+	/* If running within a container use the container namespace */
+	if (current->nsproxy->net_ns != &init_net)
+		flags |= UMH_USE_NS;
+
 	ret = install_user_keyrings();
 	if (ret < 0)
 		goto error_alloc;
@@ -172,8 +217,7 @@ static int call_sbin_request_key(struct key_construction *cons,
 	argv[i] = NULL;
 
 	/* do it */
-	ret = call_usermodehelper_keys(argv[0], argv, envp, keyring,
-				       UMH_WAIT_PROC);
+	ret = call_usermodehelper_keys(argv[0], argv, envp, keyring, flags);
 	kdebug("usermode -> 0x%x", ret);
 	if (ret >= 0) {
 		/* ret is the exit/wait code */