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Subject[PATCH] [6/9] SYSCTL: Convert modprobe_path to proc_rcu_string()
Date

Avoids races with lockless sysctl

Also saves ~220 bytes in the data segment for default kernels.

Signed-off-by: Andi Kleen <ak@linux.intel.com>

---
kernel/kmod.c | 36 ++++++++++++++++++++++++++++--------
kernel/sysctl.c | 4 ++--
2 files changed, 30 insertions(+), 10 deletions(-)

Index: linux-2.6.33-rc2-ak/kernel/kmod.c
===================================================================
--- linux-2.6.33-rc2-ak.orig/kernel/kmod.c
+++ linux-2.6.33-rc2-ak/kernel/kmod.c
@@ -35,6 +35,7 @@
#include <linux/resource.h>
#include <linux/notifier.h>
#include <linux/suspend.h>
+#include <linux/rcustring.h>
#include <asm/uaccess.h>

#include <trace/events/module.h>
@@ -48,7 +49,12 @@ static struct workqueue_struct *khelper_
/*
modprobe_path is set via /proc/sys.
*/
-char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
+char *modprobe_path = "/sbin/modprobe";
+
+static void free_arg(char **argv, char **env)
+{
+ kfree(argv[0]);
+}

/**
* __request_module - try to load a kernel module
@@ -71,7 +77,8 @@ int __request_module(bool wait, const ch
char module_name[MODULE_NAME_LEN];
unsigned int max_modprobes;
int ret;
- char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
+ char *mp_copy;
+ char *argv[] = { NULL, "-q", "--", module_name, NULL };
static char *envp[] = { "HOME=/",
"TERM=linux",
"PATH=/sbin:/usr/sbin:/bin:/usr/bin",
@@ -80,15 +87,24 @@ int __request_module(bool wait, const ch
#define MAX_KMOD_CONCURRENT 50 /* Completely arbitrary value - KAO */
static int kmod_loop_msg;

+ /* Get a stable-over-sleeps private copy of modprobe_path */
+ mp_copy = access_rcu_string(&modprobe_path, KMOD_PATH_LEN,
+ wait ? GFP_KERNEL : GFP_ATOMIC);
+ if (!mp_copy)
+ return -ENOMEM;
+ argv[0] = mp_copy;
+
va_start(args, fmt);
ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
va_end(args);
- if (ret >= MODULE_NAME_LEN)
- return -ENAMETOOLONG;
+ if (ret >= MODULE_NAME_LEN) {
+ ret = -ENAMETOOLONG;
+ goto error;
+ }

ret = security_kernel_module_request(module_name);
if (ret)
- return ret;
+ goto error;

/* 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
@@ -111,14 +127,18 @@ int __request_module(bool wait, const ch
"request_module: runaway loop modprobe %s\n",
module_name);
atomic_dec(&kmod_concurrent);
- return -ENOMEM;
+ ret = -ENOMEM;
+ goto error;
}

trace_module_request(module_name, wait, _RET_IP_);

- ret = call_usermodehelper(modprobe_path, argv, envp,
- wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
+ ret = call_usermodehelper_cleanup(mp_copy, argv, envp,
+ wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC, free_arg);
+ mp_copy = NULL; /* free_arg frees */
atomic_dec(&kmod_concurrent);
+error:
+ kfree(mp_copy);
return ret;
}
EXPORT_SYMBOL(__request_module);
Index: linux-2.6.33-rc2-ak/kernel/sysctl.c
===================================================================
--- linux-2.6.33-rc2-ak.orig/kernel/sysctl.c
+++ linux-2.6.33-rc2-ak/kernel/sysctl.c
@@ -121,7 +121,7 @@ static int min_percpu_pagelist_fract = 8
static int ngroups_max = NGROUPS_MAX;

#ifdef CONFIG_MODULES
-extern char modprobe_path[];
+extern char *modprobe_path;
extern int modules_disabled;
#endif
#ifdef CONFIG_CHR_DEV_SG
@@ -532,7 +532,7 @@ static struct ctl_table kern_table[] = {
.data = &modprobe_path,
.maxlen = KMOD_PATH_LEN,
.mode = 0644,
- .proc_handler = proc_dostring,
+ .proc_handler = proc_rcu_string,
},
{
.procname = "modules_disabled",

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