[PATCH] Keys: Pass session keyring to call_usermodehelper()

The attached patch makes it possible to pass a session keyring through to the
process spawned by call_usermodehelper().  This allows patch 3/3 to pass an
authorisation key through to /sbin/request-key, thus permitting better access
controls when doing just-in-time key creation.

Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

4 files changed, 35 insertions, 7 deletions

diff --git a/include/linux/key.h b/include/linux/key.h
index 2c24ffaca86f..2bfbf88d2740 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -273,14 +273,22 @@ extern void key_fsuid_changed(struct task_struct *tsk);
 extern void key_fsgid_changed(struct task_struct *tsk);
 extern void key_init(void);
 
+#define __install_session_keyring(tsk, keyring)                 \
+({                                                              \
+        struct key *old_session = tsk->signal->session_keyring; \
+        tsk->signal->session_keyring = keyring;                 \
+        old_session;                                            \
+})
+
 #else /* CONFIG_KEYS */
 
 #define key_validate(k)                 0
 #define key_serial(k)                   0
-#define key_get(k)                      NULL
+#define key_get(k)                      ({ NULL; })
 #define key_put(k)                      do { } while(0)
 #define alloc_uid_keyring(u)            0
 #define switch_uid_keyring(u)           do { } while(0)
+#define __install_session_keyring(t, k) ({ NULL; })
 #define copy_keys(f,t)                  0
 #define copy_thread_group_keys(t)       0
 #define exit_keys(t)                    do { } while(0)
diff --git a/include/linux/kmod.h b/include/linux/kmod.h
index 95d0e4b0814d..e4a231549407 100644
--- a/include/linux/kmod.h
+++ b/include/linux/kmod.h
@@ -19,6 +19,7 @@
  *      Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include <linux/stddef.h>
 #include <linux/config.h>
 #include <linux/errno.h>
 #include <linux/compiler.h>
@@ -34,7 +35,17 @@ static inline int request_module(const char * name, ...) { return -ENOSYS; }
 #endif
 
 #define try_then_request_module(x, mod...) ((x) ?: (request_module(mod), (x)))
-extern int call_usermodehelper(char *path, char *argv[], char *envp[], int wait);
+
+struct key;
+extern int call_usermodehelper_keys(char *path, char *argv[], char *envp[],
+                                    struct key *session_keyring, int wait);
+
+static inline int
+call_usermodehelper(char *path, char **argv, char **envp, int wait)
+{
+        return call_usermodehelper_keys(path, argv, envp, NULL, wait);
+}
+
 extern void usermodehelper_init(void);
 
 #endif /* __LINUX_KMOD_H__ */
diff --git a/kernel/kmod.c b/kernel/kmod.c
index eed53d4f5230..44166e3bb8af 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -120,6 +120,7 @@ struct subprocess_info {
         char *path;
         char **argv;
         char **envp;
+        struct key *ring;
         int wait;
         int retval;
 };
@@ -130,16 +131,21 @@ struct subprocess_info {
 static int ____call_usermodehelper(void *data)
 {
         struct subprocess_info *sub_info = data;
+        struct key *old_session;
         int retval;
 
-        /* Unblock all signals. */
+        /* Unblock all signals and set the session keyring. */
+        key_get(sub_info->ring);
         flush_signals(current);
         spin_lock_irq(&current->sighand->siglock);
+        old_session = __install_session_keyring(current, sub_info->ring);
         flush_signal_handlers(current, 1);
         sigemptyset(&current->blocked);
         recalc_sigpending();
         spin_unlock_irq(&current->sighand->siglock);
 
+        key_put(old_session);
+
         /* We can run anywhere, unlike our parent keventd(). */
         set_cpus_allowed(current, CPU_MASK_ALL);
 
@@ -211,10 +217,11 @@ static void __call_usermodehelper(void *data)
 }
 
 /**
- * call_usermodehelper - start a usermode application
+ * call_usermodehelper_keys - start a usermode application
  * @path: pathname for the application
  * @argv: null-terminated argument list
  * @envp: null-terminated environment list
+ * @session_keyring: session keyring for process (NULL for an empty keyring)
  * @wait: wait for the application to finish and return status.
  *
  * Runs a user-space application.  The application is started
@@ -224,7 +231,8 @@ static void __call_usermodehelper(void *data)
  * Must be called from process context.  Returns a negative error code
  * if program was not execed successfully, or 0.
  */
-int call_usermodehelper(char *path, char **argv, char **envp, int wait)
+int call_usermodehelper_keys(char *path, char **argv, char **envp,
+                             struct key *session_keyring, int wait)
 {
         DECLARE_COMPLETION(done);
         struct subprocess_info sub_info = {
@@ -232,6 +240,7 @@ int call_usermodehelper(char *path, char **argv, char **envp, int wait)
                 .path           = path,
                 .argv           = argv,
                 .envp           = envp,
+                .ring           = session_keyring,
                 .wait           = wait,
                 .retval         = 0,
         };
@@ -247,7 +256,7 @@ int call_usermodehelper(char *path, char **argv, char **envp, int wait)
         wait_for_completion(&done);
         return sub_info.retval;
 }
-EXPORT_SYMBOL(call_usermodehelper);
+EXPORT_SYMBOL(call_usermodehelper_keys);
 
 void __init usermodehelper_init(void)
 {
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 1f6c0940297f..1919540f047d 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -88,7 +88,7 @@ static int call_request_key(struct key *key,
         argv[i] = NULL;
 
         /* do it */
-        return call_usermodehelper(argv[0], argv, envp, 1);
+        return call_usermodehelper_keys(argv[0], argv, envp, NULL, 1);
 
 } /* end call_request_key() */