umh: creds: convert call_usermodehelper_keys() to use subprocess_info->init()

call_usermodehelper_keys() uses call_usermodehelper_setkeys() to change
subprocess_info->cred in advance.  Now that we have info->init() we can
change this code to set tgcred->session_keyring in context of execing
kernel thread.

Note: since currently call_usermodehelper_keys() is never called with
UMH_NO_WAIT, call_usermodehelper_keys()->key_get() and umh_keys_cleanup()
are not really needed, we could rely on install_session_keyring_to_cred()
which does key_get() on success.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 34 insertions, 2 deletions

diff --git a/security/keys/internal.h b/security/keys/internal.h
index 5d4402a1161a..38783dcf6c61 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -124,6 +124,7 @@ extern struct key *find_keyring_by_name(const char *name, bool skip_perm_check);
 extern int install_user_keyrings(void);
 extern int install_thread_keyring_to_cred(struct cred *);
 extern int install_process_keyring_to_cred(struct cred *);
+extern int install_session_keyring_to_cred(struct cred *, struct key *);
 
 extern struct key *request_key_and_link(struct key_type *type,
                                         const char *description,
diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index 20a38fed61b1..6b8e4ff4cc68 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -216,8 +216,7 @@ static int install_process_keyring(void)
 /*
  * install a session keyring directly to a credentials struct
  */
-static int install_session_keyring_to_cred(struct cred *cred,
-                                           struct key *keyring)
+int install_session_keyring_to_cred(struct cred *cred, struct key *keyring)
 {
         unsigned long flags;
         struct key *old;
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index f656e9c069e3..f5ec9ac5d57c 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -58,6 +58,38 @@ void complete_request_key(struct key_construction *cons, int error)
 }
 EXPORT_SYMBOL(complete_request_key);
 
+static int umh_keys_init(struct subprocess_info *info)
+{
+        struct cred *cred = (struct cred*)current_cred();
+        struct key *keyring = info->data;
+        /*
+         * This is called in context of freshly forked kthread before
+         * kernel_execve(), we can just change our ->session_keyring.
+         */
+        return install_session_keyring_to_cred(cred, keyring);
+}
+
+static void umh_keys_cleanup(struct subprocess_info *info)
+{
+        struct key *keyring = info->data;
+        key_put(keyring);
+}
+
+static int call_usermodehelper_keys(char *path, char **argv, char **envp,
+                         struct key *session_keyring, enum umh_wait wait)
+{
+        gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
+        struct subprocess_info *info =
+                call_usermodehelper_setup(path, argv, envp, gfp_mask);
+
+        if (!info)
+                return -ENOMEM;
+
+        call_usermodehelper_setfns(info, umh_keys_init, umh_keys_cleanup,
+                                        key_get(session_keyring));
+        return call_usermodehelper_exec(info, wait);
+}
+
 /*
  * request userspace finish the construction of a key
  * - execute "/sbin/request-key <op> <key> <uid> <gid> <keyring> <keyring> <keyring>"