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Message-ID: <20130520070017.7957.9224.stgit@localhost.localdomain>
Date: Mon, 20 May 2013 11:00:37 +0400
From: Stanislav Kinsbursky <skinsbursky@...allels.com>
To: akpm@...ux-foundation.org
Cc: jlayton@...hat.com, lucas.demarchi@...fusion.mobi,
rusty@...tcorp.com.au, linux-kernel@...r.kernel.org,
oleg@...hat.com, bfields@...ldses.org, viro@...iv.linux.org.uk,
bharrosh@...asas.com, devel@...nvz.org
Subject: [RFC PATCH] kmod: add ability to swap root in usermode helper
Usermode helper executes all binaries in global "init" root context. This
doesn't allow to call to call the binary from other root (for example in a
container).
Currently, containerized NFS server requires an ability to execute a binary in
a other context, than "init" root (UMH is used for client recovery tracking).
This patch adds root swap to ____call_usermodehelper(), if non-NULL root was
passed as a part of subprocess_info data, and a call_usermodehelper_root()
helper, which accept root as a parameter. Root path reference must be hold by
the caller, since it will be on UMH thread exit.
Signed-off-by: Stanislav Kinsbursky <skinsbursky@...allels.com>
---
include/linux/kmod.h | 9 +++++++++
kernel/kmod.c | 41 ++++++++++++++++++++++++++++++++++-------
2 files changed, 43 insertions(+), 7 deletions(-)
diff --git a/include/linux/kmod.h b/include/linux/kmod.h
index 0555cc6..0b041c7 100644
--- a/include/linux/kmod.h
+++ b/include/linux/kmod.h
@@ -64,12 +64,21 @@ struct subprocess_info {
int (*init)(struct subprocess_info *info, struct cred *new);
void (*cleanup)(struct subprocess_info *info);
void *data;
+ struct path *root;
};
extern int
+call_usermodehelper_root(char *path, char **argv, char **envp, int wait,
+ struct path *root);
+extern int
call_usermodehelper(char *path, char **argv, char **envp, int wait);
extern struct subprocess_info *
+call_usermodehelper_setup_root(char *path, char **argv, char **envp, gfp_t gfp_mask,
+ int (*init)(struct subprocess_info *info, struct cred *new),
+ void (*cleanup)(struct subprocess_info *), void *data,
+ struct path *root);
+extern struct subprocess_info *
call_usermodehelper_setup(char *path, char **argv, char **envp, gfp_t gfp_mask,
int (*init)(struct subprocess_info *info, struct cred *new),
void (*cleanup)(struct subprocess_info *), void *data);
diff --git a/kernel/kmod.c b/kernel/kmod.c
index 1296e72..1b41f2c 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -39,6 +39,7 @@
#include <linux/rwsem.h>
#include <linux/ptrace.h>
#include <linux/async.h>
+#include <linux/fs_struct.h>
#include <asm/uaccess.h>
#include <trace/events/module.h>
@@ -215,6 +216,9 @@ static int ____call_usermodehelper(void *data)
*/
set_user_nice(current, 0);
+ if (sub_info->root)
+ set_fs_root(current->fs, sub_info->root);
+
retval = -ENOMEM;
new = prepare_kernel_cred(current);
if (!new)
@@ -505,7 +509,7 @@ static void helper_unlock(void)
}
/**
- * call_usermodehelper_setup - prepare to call a usermode helper
+ * call_usermodehelper_setup_root - prepare to call a usermode helper
* @path: path to usermode executable
* @argv: arg vector for process
* @envp: environment for process
@@ -513,6 +517,7 @@ static void helper_unlock(void)
* @cleanup: a cleanup function
* @init: an init function
* @data: arbitrary context sensitive data
+ * @root: fs root to swap to before binary execution
*
* Returns either %NULL on allocation failure, or a subprocess_info
* structure. This should be passed to call_usermodehelper_exec to
@@ -527,11 +532,11 @@ static void helper_unlock(void)
* Function must be runnable in either a process context or the
* context in which call_usermodehelper_exec is called.
*/
-struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
+struct subprocess_info *call_usermodehelper_setup_root(char *path, char **argv,
char **envp, gfp_t gfp_mask,
int (*init)(struct subprocess_info *info, struct cred *new),
void (*cleanup)(struct subprocess_info *info),
- void *data)
+ void *data, struct path *root)
{
struct subprocess_info *sub_info;
sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
@@ -546,9 +551,22 @@ struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
sub_info->cleanup = cleanup;
sub_info->init = init;
sub_info->data = data;
+
+ sub_info->root = root;
out:
return sub_info;
}
+EXPORT_SYMBOL(call_usermodehelper_setup_root);
+
+struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
+ char **envp, gfp_t gfp_mask,
+ int (*init)(struct subprocess_info *info, struct cred *new),
+ void (*cleanup)(struct subprocess_info *info),
+ void *data)
+{
+ return call_usermodehelper_setup_root(path, argv, envp, gfp_mask, init,
+ cleanup, data, NULL);
+}
EXPORT_SYMBOL(call_usermodehelper_setup);
/**
@@ -617,7 +635,7 @@ unlock:
EXPORT_SYMBOL(call_usermodehelper_exec);
/**
- * call_usermodehelper() - prepare and start a usermode application
+ * call_usermodehelper_root() - prepare and start a usermode application
* @path: path to usermode executable
* @argv: arg vector for process
* @envp: environment for process
@@ -625,24 +643,33 @@ EXPORT_SYMBOL(call_usermodehelper_exec);
* when UMH_NO_WAIT 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
* from interrupt context.
+ * @root: fs root to swap to before binary execution
*
* This function is the equivalent to use call_usermodehelper_setup() and
* call_usermodehelper_exec().
*/
-int call_usermodehelper(char *path, char **argv, char **envp, int wait)
+int call_usermodehelper_root(char *path, char **argv, char **envp, int wait,
+ struct path *root)
{
struct subprocess_info *info;
gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
- info = call_usermodehelper_setup(path, argv, envp, gfp_mask,
- NULL, NULL, NULL);
+ info = call_usermodehelper_setup_root(path, argv, envp, gfp_mask,
+ NULL, NULL, NULL, root);
if (info == NULL)
return -ENOMEM;
return call_usermodehelper_exec(info, wait);
}
+EXPORT_SYMBOL(call_usermodehelper_root);
+
+int call_usermodehelper(char *path, char **argv, char **envp, int wait)
+{
+ return call_usermodehelper_root(path, argv, envp, wait, NULL);
+}
EXPORT_SYMBOL(call_usermodehelper);
+
static int proc_cap_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos)
{
--
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