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From: Rusty Russell <rusty@rustcorp.com.au>
To: Thomas Sailer <sailer@scs.ch>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, akpm@zip.com.au,
       Jose Orlando Pereira <jop@di.uminho.pt>,
       J.E.J.Bottomley@HansenPartnership.com
Subject: Re: [PATCH] Deprecate exec_usermodehelper, fix request_module. 
In-reply-to: Your message of "02 Jan 2003 20:08:28 BST."
             <1041534508.2074.32.camel@gamecube> 
Date: Fri, 03 Jan 2003 16:08:38 +1100
Message-Id: <20030103050859.4E01B2C070@lists.samba.org>
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In message <1041534508.2074.32.camel@gamecube> you write:
> On Thu, 2003-01-02 at 18:14, Marcel Holtmann wrote:
> 
> > for the bt3c_cs driver I need to run a user space program that downloads
> > the firmware into the card and the kernel part have to wait until this
> > program has finished. So what is the best way to do this now?
> 
> We all seem to have the same problem 8-)
> 
> Rusty's new proposal with the wait argument seems to solve our problem,
> except that it would be nice if there was a way to retrieve the exit
> status of the user mode helper program.

OK, how's this.  Positive means it's the exit code (only if wait is
set).

Cheers!
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Name: call_usermodehelper can wait for us: exec_usermodehelper sucks
Author: Rusty Russell
Status: Tested on 2.5.54

D: Urban Widmark points out that modprobe calls system() in many
D: configurations, which drops privs since request_module() doesn't
D: doesn't set ruid and rguid.
D:
D: Use a known-clean environment (as call_usermodehelper does).
D: Deprecate exec_usermodehelper, since it's probably buggy, maybe
D: exploitable.

diff -urNp --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5-bk/include/linux/kmod.h working-2.5-bk-kmod-noclean/include/linux/kmod.h
--- linux-2.5-bk/include/linux/kmod.h	Thu Jan  2 12:35:15 2003
+++ working-2.5-bk-kmod-noclean/include/linux/kmod.h	Fri Jan  3 14:50:30 2003
@@ -21,6 +21,7 @@
 
 #include <linux/config.h>
 #include <linux/errno.h>
+#include <linux/compiler.h>
 
 #ifdef CONFIG_KMOD
 extern int request_module(const char * name);
@@ -29,8 +30,8 @@ static inline int request_module(const c
 #endif
 
 #define try_then_request_module(x, mod) ((x) ?: request_module(mod), (x))
-extern int exec_usermodehelper(char *program_path, char *argv[], char *envp[]);
-extern int call_usermodehelper(char *path, char *argv[], char *envp[]);
+extern int exec_usermodehelper(char *program_path, char *argv[], char *envp[])  __deprecated;
+extern int call_usermodehelper(char *path, char *argv[], char *envp[], int wait);
 
 #ifdef CONFIG_HOTPLUG
 extern char hotplug_path [];
diff -urNp --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5-bk/kernel/kmod.c working-2.5-bk-kmod-noclean/kernel/kmod.c
--- linux-2.5-bk/kernel/kmod.c	Thu Jan  2 12:37:03 2003
+++ working-2.5-bk-kmod-noclean/kernel/kmod.c	Fri Jan  3 16:02:55 2003
@@ -14,8 +14,10 @@
 
 	Unblock all signals when we exec a usermode process.
 	Shuu Yamaguchi <shuu@wondernetworkresources.com> December 2000
-*/
 
+	call_usermodehelper wait flag, and deprecate exec_usermodehelper.
+	Rusty Russell <rusty@rustcorp.com.au>  Jan 2003
+*/
 #define __KERNEL_SYSCALLS__
 
 #include <linux/config.h>
@@ -31,6 +33,7 @@
 #include <linux/workqueue.h>
 #include <linux/security.h>
 #include <linux/mount.h>
+#include <linux/kernel.h>
 #include <asm/uaccess.h>
 
 extern int max_threads, system_running;
@@ -153,29 +156,6 @@ int exec_usermodehelper(char *program_pa
 */
 char modprobe_path[256] = "/sbin/modprobe";
 
-static int exec_modprobe(void * module_name)
-{
-	static char * envp[] = { "HOME=/", "TERM=linux", "PATH=/sbin:/usr/sbin:/bin:/usr/bin", NULL };
-	char *argv[] = { modprobe_path, "--", (char*)module_name, NULL };
-	int ret;
-
-	if (!system_running)
-		return -EBUSY;
-
-	ret = exec_usermodehelper(modprobe_path, argv, envp);
-	if (ret) {
-		static unsigned long last;
-		unsigned long now = jiffies;
-		if (now - last > HZ) {
-			last = now;
-			printk(KERN_DEBUG
-			       "kmod: failed to exec %s -s -k %s, errno = %d\n",
-			       modprobe_path, (char*) module_name, errno);
-		}
-	}
-	return ret;
-}
-
 /**
  * request_module - try to load a kernel module
  * @module_name: Name of module
@@ -189,24 +169,18 @@ static int exec_modprobe(void * module_n
  * If module auto-loading support is disabled then this function
  * becomes a no-operation.
  */
-int request_module(const char * module_name)
+int request_module(const char *module_name)
 {
-	pid_t pid;
-	int waitpid_result;
-	sigset_t tmpsig;
-	int i, ret;
+	unsigned int max_modprobes;
+	int ret;
+	char *argv[] = { modprobe_path, "--", (char*)module_name, NULL };
+	static char *envp[] = { "HOME=/",
+				"TERM=linux",
+				"PATH=/sbin:/usr/sbin:/bin:/usr/bin",
+				NULL };
 	static atomic_t kmod_concurrent = ATOMIC_INIT(0);
 #define MAX_KMOD_CONCURRENT 50	/* Completely arbitrary value - KAO */
 	static int kmod_loop_msg;
-	unsigned long saved_policy = current->policy;
-
-	current->policy = SCHED_NORMAL;
-	/* Don't allow request_module() when the system isn't set up */
-	if ( ! system_running ) {
-		printk(KERN_ERR "request_module[%s]: not ready\n", module_name);
-		ret = -EPERM;
-		goto out;
-	}
 
 	/* If modprobe needs a service that is in a module, we get a recursive
 	 * loop.  Limit the number of running kmod threads to max_threads/2 or
@@ -216,56 +190,39 @@ int request_module(const char * module_n
 	 * process tables to get the command line, proc_pid_cmdline is static
 	 * and it is not worth changing the proc code just to handle this case. 
 	 * KAO.
+	 *
+
+	 * "trace the ppid" is simple, but will fail if someone's
+	 * parent exits.  I think this is as good as it gets. --RR
 	 */
-	i = max_threads/2;
-	if (i > MAX_KMOD_CONCURRENT)
-		i = MAX_KMOD_CONCURRENT;
+	max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
 	atomic_inc(&kmod_concurrent);
-	if (atomic_read(&kmod_concurrent) > i) {
+	if (atomic_read(&kmod_concurrent) > max_modprobes) {
+		/* We may be blaming an innocent here, but unlikely */
 		if (kmod_loop_msg++ < 5)
 			printk(KERN_ERR
-			       "kmod: runaway modprobe loop assumed and stopped\n");
+			       "request_module: runaway loop modprobe %s\n",
+			       module_name);
 		atomic_dec(&kmod_concurrent);
-		ret = -ENOMEM;
-		goto out;
+		return -ENOMEM;
 	}
 
-	pid = kernel_thread(exec_modprobe, (void*) module_name, 0);
-	if (pid < 0) {
-		printk(KERN_ERR "request_module[%s]: fork failed, errno %d\n", module_name, -pid);
-		atomic_dec(&kmod_concurrent);
-		ret = pid;
-		goto out;
+	ret = call_usermodehelper(modprobe_path, argv, envp, 1);
+	if (ret < 0) { /* Exec failed, or fork failed or something bad */
+		static unsigned long last;
+		unsigned long now = jiffies;
+		if (now - last > HZ) {
+			last = now;
+			printk(KERN_DEBUG
+			       "request_module: failed %s -- %s. error = %d\n",
+			       modprobe_path, module_name, -ret);
+		}
 	}
-
-	/* Block everything but SIGKILL/SIGSTOP */
-	spin_lock_irq(&current->sig->siglock);
-	tmpsig = current->blocked;
-	siginitsetinv(&current->blocked, sigmask(SIGKILL) | sigmask(SIGSTOP));
-	recalc_sigpending();
-	spin_unlock_irq(&current->sig->siglock);
-
-	waitpid_result = waitpid(pid, NULL, __WCLONE);
 	atomic_dec(&kmod_concurrent);
-
-	/* Allow signals again.. */
-	spin_lock_irq(&current->sig->siglock);
-	current->blocked = tmpsig;
-	recalc_sigpending();
-	spin_unlock_irq(&current->sig->siglock);
-
-	if (waitpid_result != pid) {
-		printk(KERN_ERR "request_module[%s]: waitpid(%d,...) failed, errno %d\n",
-		       module_name, pid, -waitpid_result);
-	}
-	ret = 0;
-out:
-	current->policy = saved_policy;
-	return ret;
+	return ret < 0 ? ret : 0;
 }
 #endif /* CONFIG_KMOD */
 
-
 #ifdef CONFIG_HOTPLUG
 /*
 	hotplug path is set via /proc/sys
@@ -294,7 +251,8 @@ struct subprocess_info {
 	char *path;
 	char **argv;
 	char **envp;
-	pid_t retval;
+	int wait;
+	int retval;
 };
 
 /*
@@ -310,10 +268,27 @@ static int ____call_usermodehelper(void 
 		retval = exec_usermodehelper(sub_info->path, sub_info->argv, sub_info->envp);
 
 	/* Exec failed? */
-	sub_info->retval = (pid_t)retval;
+	sub_info->retval = retval;
 	do_exit(0);
 }
 
+/* Keventd can't block, but this (a child) can. */
+static int wait_for_helper(void *data)
+{
+	struct subprocess_info *sub_info = data;
+	pid_t pid;
+
+	pid = kernel_thread(____call_usermodehelper, sub_info,
+			    CLONE_VFORK | SIGCHLD);
+	if (pid < 0)
+		sub_info->retval = pid;
+	else
+		sys_wait4(pid, (unsigned int *)&sub_info->retval, 0, NULL);
+
+	complete(sub_info->complete);
+	return 0;
+}
+
 /*
  * This is run by keventd.
  */
@@ -322,14 +297,21 @@ static void __call_usermodehelper(void *
 	struct subprocess_info *sub_info = data;
 	pid_t pid;
 
-	/*
-	 * CLONE_VFORK: wait until the usermode helper has execve'd successfully
-	 * We need the data structures to stay around until that is done.
-	 */
-	pid = kernel_thread(____call_usermodehelper, sub_info, CLONE_VFORK | SIGCHLD);
-	if (pid < 0)
+	/* CLONE_VFORK: wait until the usermode helper has execve'd
+	 * successfully We need the data structures to stay around
+	 * until that is done.  */
+	if (sub_info->wait)
+		pid = kernel_thread(wait_for_helper, sub_info,
+				    CLONE_KERNEL | SIGCHLD);
+	else
+		pid = kernel_thread(____call_usermodehelper, sub_info,
+				    CLONE_VFORK | SIGCHLD);
+
+	if (pid < 0) {
 		sub_info->retval = pid;
-	complete(sub_info->complete);
+		complete(sub_info->complete);
+	} else if (!sub_info->wait)
+		complete(sub_info->complete);
 }
 
 /**
@@ -337,15 +319,17 @@ static void __call_usermodehelper(void *
  * @path: pathname for the application
  * @argv: null-terminated argument list
  * @envp: null-terminated environment list
+ * @wait: wait for the application to finish and return status.
  *
- * Runs a user-space application.  The application is started asynchronously.  It
- * runs as a child of keventd.  It runs with full root capabilities.  keventd silently
- * reaps the child when it exits.
+ * 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 zero on success, else a negative
- * error code.
+ * Must be called from process context.  Returns a negative error code
+ * if program was not execed successfully, or (exitcode << 8 + signal)
+ * of the application (0 if wait is not set).
  */
-int call_usermodehelper(char *path, char **argv, char **envp)
+int call_usermodehelper(char *path, char **argv, char **envp, int wait)
 {
 	DECLARE_COMPLETION(done);
 	struct subprocess_info sub_info = {
@@ -353,6 +337,7 @@ int call_usermodehelper(char *path, char
 		.path		= path,
 		.argv		= argv,
 		.envp		= envp,
+		.wait		= wait,
 		.retval		= 0,
 	};
 	DECLARE_WORK(work, __call_usermodehelper, &sub_info);
diff -urNp --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5-bk/drivers/acpi/thermal.c working-2.5-bk-kmod-noclean/drivers/acpi/thermal.c
--- linux-2.5-bk/drivers/acpi/thermal.c	Thu Jan  2 12:47:01 2003
+++ working-2.5-bk-kmod-noclean/drivers/acpi/thermal.c	Fri Jan  3 14:50:30 2003
@@ -431,7 +431,7 @@ acpi_thermal_call_usermode (
 	envp[0] = "HOME=/";
 	envp[1] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
 	
-	call_usermodehelper(argv[0], argv, envp);
+	call_usermodehelper(argv[0], argv, envp, 0);
 
 	return_VALUE(0);
 }
diff -urNp --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5-bk/drivers/base/hotplug.c working-2.5-bk-kmod-noclean/drivers/base/hotplug.c
--- linux-2.5-bk/drivers/base/hotplug.c	Thu Jan  2 12:46:16 2003
+++ working-2.5-bk-kmod-noclean/drivers/base/hotplug.c	Fri Jan  3 14:50:30 2003
@@ -114,7 +114,7 @@ static int do_hotplug (struct device *de
 
 	pr_debug ("%s: %s %s %s %s %s %s\n", __FUNCTION__, argv [0], argv[1],
 		  envp[0], envp[1], envp[2], envp[3]);
-	retval = call_usermodehelper (argv [0], argv, envp);
+	retval = call_usermodehelper (argv [0], argv, envp, 0);
 	if (retval)
 		pr_debug ("%s - call_usermodehelper returned %d\n",
 			  __FUNCTION__, retval);
diff -urNp --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5-bk/drivers/ieee1394/nodemgr.c working-2.5-bk-kmod-noclean/drivers/ieee1394/nodemgr.c
--- linux-2.5-bk/drivers/ieee1394/nodemgr.c	Thu Jan  2 12:46:17 2003
+++ working-2.5-bk-kmod-noclean/drivers/ieee1394/nodemgr.c	Fri Jan  3 14:50:30 2003
@@ -786,7 +786,7 @@ static void nodemgr_call_policy(char *ve
 #ifdef CONFIG_IEEE1394_VERBOSEDEBUG
 	HPSB_DEBUG("NodeMgr: %s %s %016Lx", argv[0], verb, (long long unsigned)ud->ne->guid);
 #endif
-	value = call_usermodehelper(argv[0], argv, envp);
+	value = call_usermodehelper(argv[0], argv, envp, 0);
 	kfree(buf);
 	kfree(envp);
 	if (value != 0)
diff -urNp --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5-bk/drivers/input/input.c working-2.5-bk-kmod-noclean/drivers/input/input.c
--- linux-2.5-bk/drivers/input/input.c	Thu Jan  2 12:30:27 2003
+++ working-2.5-bk-kmod-noclean/drivers/input/input.c	Fri Jan  3 14:50:30 2003
@@ -383,7 +383,7 @@ static void input_call_hotplug(char *ver
 		argv[0], argv[1], envp[0], envp[1], envp[2], envp[3], envp[4]);
 #endif
 
-	value = call_usermodehelper(argv [0], argv, envp);
+	value = call_usermodehelper(argv [0], argv, envp, 0);
 
 	kfree(buf);
 	kfree(envp);
diff -urNp --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5-bk/drivers/isdn/hardware/eicon/divasmain.c working-2.5-bk-kmod-noclean/drivers/isdn/hardware/eicon/divasmain.c
--- linux-2.5-bk/drivers/isdn/hardware/eicon/divasmain.c	Thu Jan  2 12:45:18 2003
+++ working-2.5-bk-kmod-noclean/drivers/isdn/hardware/eicon/divasmain.c	Fri Jan  3 14:50:30 2003
@@ -263,7 +263,7 @@ static void diva_adapter_trapped(void *c
 		pdpc->card_failed = 0;
 		argv[2] = &adapter[0];
 
-		ret = call_usermodehelper(argv[0], argv, envp);
+		ret = call_usermodehelper(argv[0], argv, envp, 0);
 
 		if (ret) {
 			printk(KERN_ERR
diff -urNp --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5-bk/drivers/pnp/pnpbios/core.c working-2.5-bk-kmod-noclean/drivers/pnp/pnpbios/core.c
--- linux-2.5-bk/drivers/pnp/pnpbios/core.c	Thu Jan  2 14:47:59 2003
+++ working-2.5-bk-kmod-noclean/drivers/pnp/pnpbios/core.c	Fri Jan  3 14:50:30 2003
@@ -602,7 +602,7 @@ static int pnp_dock_event(int dock, stru
 		info->location_id, info->serial, info->capabilities);
 	envp[i] = 0;
 	
-	value = call_usermodehelper (argv [0], argv, envp);
+	value = call_usermodehelper (argv [0], argv, envp, 0);
 	kfree (buf);
 	kfree (envp);
 	return 0;
diff -urNp --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5-bk/net/bluetooth/hci_core.c working-2.5-bk-kmod-noclean/net/bluetooth/hci_core.c
--- linux-2.5-bk/net/bluetooth/hci_core.c	Thu Jan  2 12:33:56 2003
+++ working-2.5-bk-kmod-noclean/net/bluetooth/hci_core.c	Fri Jan  3 14:50:30 2003
@@ -114,7 +114,7 @@ static int hci_run_hotplug(char *dev, ch
 	envp[3] = astr;
 	envp[4] = NULL;
 	
-	return call_usermodehelper(argv[0], argv, envp);
+	return call_usermodehelper(argv[0], argv, envp, 0);
 }
 #else
 #define hci_run_hotplug(A...)
diff -urNp --exclude TAGS -X /home/rusty/current-dontdiff --minimal linux-2.5-bk/net/core/dev.c working-2.5-bk-kmod-noclean/net/core/dev.c
--- linux-2.5-bk/net/core/dev.c	Thu Jan  2 14:48:01 2003
+++ working-2.5-bk-kmod-noclean/net/core/dev.c	Fri Jan  3 14:50:30 2003
@@ -2918,6 +2918,6 @@ static int net_run_sbin_hotplug(struct n
 	envp [i++] = action_str;
 	envp [i] = 0;
 
-	return call_usermodehelper(argv [0], argv, envp);
+	return call_usermodehelper(argv [0], argv, envp, 0);
 }
 #endif
-
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