linux-kernel - [PATCH 1/4] kmod: make usermodehelper path a const string

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Date:   Wed, 14 Dec 2016 10:50:28 -0800
From:   Greg KH <gregkh@...uxfoundation.org>
To:     kernel-hardening@...ts.openwall.com
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH 1/4] kmod: make usermodehelper path a const string

This is in preparation for making it so that usermode helper programs
can't be changed, if desired, by userspace.  We will tackle the mess of
cleaning up the write-ability of argv and env later, that's going to
take more work, for much less gain...

Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 include/linux/kmod.h | 7 ++++---
 kernel/kmod.c        | 4 ++--
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/include/linux/kmod.h b/include/linux/kmod.h
index fcfd2bf14d3f..c4e441e00db5 100644
--- a/include/linux/kmod.h
+++ b/include/linux/kmod.h
@@ -56,7 +56,7 @@ struct file;
 struct subprocess_info {
 	struct work_struct work;
 	struct completion *complete;
-	char *path;
+	const char *path;
 	char **argv;
 	char **envp;
 	int wait;
@@ -67,10 +67,11 @@ struct subprocess_info {
 };
 
 extern int
-call_usermodehelper(char *path, char **argv, char **envp, int wait);
+call_usermodehelper(const char *path, char **argv, char **envp, int wait);
 
 extern struct subprocess_info *
-call_usermodehelper_setup(char *path, char **argv, char **envp, gfp_t gfp_mask,
+call_usermodehelper_setup(const 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 0277d1216f80..0c216b76afca 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -516,7 +516,7 @@ 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(const 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),
@@ -613,7 +613,7 @@ EXPORT_SYMBOL(call_usermodehelper_exec);
  * 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(const char *path, char **argv, char **envp, int wait)
 {
 	struct subprocess_info *info;
 	gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
-- 
2.10.2