usermodehelper: split setup from execution

Rather than having hundreds of variations of call_usermodehelper for
various pieces of usermode state which could be set up, split the
info allocation and initialization from the actual process execution.

This means the general pattern becomes:
 info = call_usermodehelper_setup(path, argv, envp); /* basic state */
 call_usermodehelper_<SET EXTRA STATE>(info, stuff...);	/* extra state */
 call_usermodehelper_exec(info, wait);	/* run process and free info */

This patch introduces wrappers for all the existing calling styles for
call_usermodehelper_*, but folds their implementations into one.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: David Howells <dhowells@redhat.com>
Cc: Bj?rn Steinbrink <B.Steinbrink@gmx.de>
Cc: Randy Dunlap <randy.dunlap@oracle.com>

2 files changed, 176 insertions, 59 deletions

diff --git a/include/linux/kmod.h b/include/linux/kmod.h
index 10f505c8431d..c4cbe59d9c67 100644
--- a/include/linux/kmod.h
+++ b/include/linux/kmod.h
@@ -36,13 +36,51 @@ static inline int request_module(const char * name, ...) { return -ENOSYS; }
 #define try_then_request_module(x, mod...) ((x) ?: (request_module(mod), (x)))
 
 struct key;
-extern int call_usermodehelper_keys(char *path, char *argv[], char *envp[],
-                                    struct key *session_keyring, int wait);
+struct file;
+struct subprocess_info;
+
+/* Allocate a subprocess_info structure */
+struct subprocess_info *call_usermodehelper_setup(char *path,
+                                                  char **argv, char **envp);
+
+/* Set various pieces of state into the subprocess_info structure */
+void call_usermodehelper_setkeys(struct subprocess_info *info,
+                                 struct key *session_keyring);
+int call_usermodehelper_stdinpipe(struct subprocess_info *sub_info,
+                                  struct file **filp);
+void call_usermodehelper_setcleanup(struct subprocess_info *info,
+                                    void (*cleanup)(char **argv, char **envp));
+
+/* Actually execute the sub-process */
+int call_usermodehelper_exec(struct subprocess_info *info, int wait);
+
+/* Free the subprocess_info. This is only needed if you're not going
+   to call call_usermodehelper_exec */
+void call_usermodehelper_freeinfo(struct subprocess_info *info);
 
 static inline int
 call_usermodehelper(char *path, char **argv, char **envp, int wait)
 {
-        return call_usermodehelper_keys(path, argv, envp, NULL, wait);
+        struct subprocess_info *info;
+
+        info = call_usermodehelper_setup(path, argv, envp);
+        if (info == NULL)
+                return -ENOMEM;
+        return call_usermodehelper_exec(info, wait);
+}
+
+static inline int
+call_usermodehelper_keys(char *path, char **argv, char **envp,
+                         struct key *session_keyring, int wait)
+{
+        struct subprocess_info *info;
+
+        info = call_usermodehelper_setup(path, argv, envp);
+        if (info == NULL)
+                return -ENOMEM;
+
+        call_usermodehelper_setkeys(info, session_keyring);
+        return call_usermodehelper_exec(info, wait);
 }
 
 extern void usermodehelper_init(void);
diff --git a/kernel/kmod.c b/kernel/kmod.c
index 4d32eb077179..d2dce71115d8 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -122,6 +122,7 @@ struct subprocess_info {
         int wait;
         int retval;
         struct file *stdin;
+        void (*cleanup)(char **argv, char **envp);
 };
 
 /*
@@ -180,6 +181,14 @@ static int ____call_usermodehelper(void *data)
         do_exit(0);
 }
 
+void call_usermodehelper_freeinfo(struct subprocess_info *info)
+{
+        if (info->cleanup)
+                (*info->cleanup)(info->argv, info->envp);
+        kfree(info);
+}
+EXPORT_SYMBOL(call_usermodehelper_freeinfo);
+
 /* Keventd can't block, but this (a child) can. */
 static int wait_for_helper(void *data)
 {
@@ -217,7 +226,7 @@ static int wait_for_helper(void *data)
         }
 
         if (sub_info->wait < 0)
-                kfree(sub_info);
+                call_usermodehelper_freeinfo(sub_info);
         else
                 complete(sub_info->complete);
         return 0;
@@ -252,11 +261,94 @@ static void __call_usermodehelper(struct work_struct *work)
 }
 
 /**
- * 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)
+ * call_usermodehelper_setup - prepare to call a usermode helper
+ * @path - path to usermode executable
+ * @argv - arg vector for process
+ * @envp - environment for process
+ *
+ * Returns either NULL on allocation failure, or a subprocess_info
+ * structure.  This should be passed to call_usermodehelper_exec to
+ * exec the process and free the structure.
+ */
+struct subprocess_info *call_usermodehelper_setup(char *path,
+                                                  char **argv, char **envp)
+{
+        struct subprocess_info *sub_info;
+        sub_info = kzalloc(sizeof(struct subprocess_info),  GFP_ATOMIC);
+        if (!sub_info)
+                goto out;
+
+        INIT_WORK(&sub_info->work, __call_usermodehelper);
+        sub_info->path = path;
+        sub_info->argv = argv;
+        sub_info->envp = envp;
+
+  out:
+        return sub_info;
+}
+EXPORT_SYMBOL(call_usermodehelper_setup);
+
+/**
+ * call_usermodehelper_setkeys - set the session keys for usermode helper
+ * @info: a subprocess_info returned by call_usermodehelper_setup
+ * @session_keyring: the session keyring for the process
+ */
+void call_usermodehelper_setkeys(struct subprocess_info *info,
+                                 struct key *session_keyring)
+{
+        info->ring = session_keyring;
+}
+EXPORT_SYMBOL(call_usermodehelper_setkeys);
+
+/**
+ * call_usermodehelper_setcleanup - set a cleanup function
+ * @info: a subprocess_info returned by call_usermodehelper_setup
+ * @cleanup: a cleanup function
+ *
+ * The cleanup function is just befor ethe subprocess_info is about to
+ * be freed.  This can be used for freeing the argv and envp.  The
+ * Function must be runnable in either a process context or the
+ * context in which call_usermodehelper_exec is called.
+ */
+void call_usermodehelper_setcleanup(struct subprocess_info *info,
+                                    void (*cleanup)(char **argv, char **envp))
+{
+        info->cleanup = cleanup;
+}
+EXPORT_SYMBOL(call_usermodehelper_setcleanup);
+
+/**
+ * call_usermodehelper_stdinpipe - set up a pipe to be used for stdin
+ * @sub_info: a subprocess_info returned by call_usermodehelper_setup
+ * @filp: set to the write-end of a pipe
+ *
+ * This constructs a pipe, and sets the read end to be the stdin of the
+ * subprocess, and returns the write-end in *@filp.
+ */
+int call_usermodehelper_stdinpipe(struct subprocess_info *sub_info,
+                                  struct file **filp)
+{
+        struct file *f;
+
+        f = create_write_pipe();
+        if (IS_ERR(f))
+                return PTR_ERR(f);
+        *filp = f;
+
+        f = create_read_pipe(f);
+        if (IS_ERR(f)) {
+                free_write_pipe(*filp);
+                return PTR_ERR(f);
+        }
+        sub_info->stdin = f;
+
+        return 0;
+}
+EXPORT_SYMBOL(call_usermodehelper_stdinpipe);
+
+/**
+ * call_usermodehelper_exec - start a usermode application
+ * @sub_info: information about the subprocessa
  * @wait: wait for the application to finish and return status.
  *        when -1 don't wait at all, but you get no useful error back when
  *        the program couldn't be exec'ed. This makes it safe to call
@@ -265,33 +357,24 @@ static void __call_usermodehelper(struct work_struct *work)
  * Runs a user-space application.  The application is started
  * asynchronously if wait is not set, and runs as a child of keventd.
  * (ie. it runs with full root capabilities).
- *
- * Must be called from process context.  Returns a negative error code
- * if program was not execed successfully, or 0.
  */
-int call_usermodehelper_keys(char *path, char **argv, char **envp,
-                             struct key *session_keyring, int wait)
+int call_usermodehelper_exec(struct subprocess_info *sub_info,
+                             int wait)
 {
         DECLARE_COMPLETION_ONSTACK(done);
-        struct subprocess_info *sub_info;
         int retval;
 
-        if (!khelper_wq)
-                return -EBUSY;
-
-        if (path[0] == '\0')
-                return 0;
+        if (sub_info->path[0] == '\0') {
+                retval = 0;
+                goto out;
+        }
 
-        sub_info = kzalloc(sizeof(struct subprocess_info),  GFP_ATOMIC);
-        if (!sub_info)
-                return -ENOMEM;
+        if (!khelper_wq) {
+                retval = -EBUSY;
+                goto out;
+        }
 
-        INIT_WORK(&sub_info->work, __call_usermodehelper);
         sub_info->complete = &done;
-        sub_info->path = path;
-        sub_info->argv = argv;
-        sub_info->envp = envp;
-        sub_info->ring = session_keyring;
         sub_info->wait = wait;
 
         queue_work(khelper_wq, &sub_info->work);
@@ -299,47 +382,43 @@ int call_usermodehelper_keys(char *path, char **argv, char **envp,
                 return 0;
         wait_for_completion(&done);
         retval = sub_info->retval;
-        kfree(sub_info);
+
+  out:
+        call_usermodehelper_freeinfo(sub_info);
         return retval;
 }
-EXPORT_SYMBOL(call_usermodehelper_keys);
+EXPORT_SYMBOL(call_usermodehelper_exec);
 
+/**
+ * call_usermodehelper_pipe - call a usermode helper process with a pipe stdin
+ * @path: path to usermode executable
+ * @argv: arg vector for process
+ * @envp: environment for process
+ * @filp: set to the write-end of a pipe
+ *
+ * This is a simple wrapper which executes a usermode-helper function
+ * with a pipe as stdin.  It is implemented entirely in terms of
+ * lower-level call_usermodehelper_* functions.
+ */
 int call_usermodehelper_pipe(char *path, char **argv, char **envp,
                              struct file **filp)
 {
-        DECLARE_COMPLETION(done);
-        struct subprocess_info sub_info = {
-                .work           = __WORK_INITIALIZER(sub_info.work,
-                                                     __call_usermodehelper),
-                .complete       = &done,
-                .path           = path,
-                .argv           = argv,
-                .envp           = envp,
-                .retval         = 0,
-        };
-        struct file *f;
-
-        if (!khelper_wq)
-                return -EBUSY;
+        struct subprocess_info *sub_info;
+        int ret;
 
-        if (path[0] == '\0')
-                return 0;
+        sub_info = call_usermodehelper_setup(path, argv, envp);
+        if (sub_info == NULL)
+                return -ENOMEM;
 
-        f = create_write_pipe();
-        if (IS_ERR(f))
-                return PTR_ERR(f);
-        *filp = f;
+        ret = call_usermodehelper_stdinpipe(sub_info, filp);
+        if (ret < 0)
+                goto out;
 
-        f = create_read_pipe(f);
-        if (IS_ERR(f)) {
-                free_write_pipe(*filp);
-                return PTR_ERR(f);
-        }
-        sub_info.stdin = f;
+        return call_usermodehelper_exec(sub_info, 1);
 
-        queue_work(khelper_wq, &sub_info.work);
-        wait_for_completion(&done);
-        return sub_info.retval;
+  out:
+        call_usermodehelper_freeinfo(sub_info);
+        return ret;
 }
 EXPORT_SYMBOL(call_usermodehelper_pipe);