linux-kernel - [ 148/153] kmod: make __request

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Date:	Mon, 04 Mar 2013 03:39:35 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org, Oleg Nesterov <oleg@...hat.com>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Tejun Heo <tj@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [ 148/153] kmod: make __request_module() killable

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Oleg Nesterov <oleg@...hat.com>

commit 1cc684ab75123efe7ff446eb821d44375ba8fa30 upstream.

As Tetsuo Handa pointed out, request_module() can stress the system
while the oom-killed caller sleeps in TASK_UNINTERRUPTIBLE.

The task T uses "almost all" memory, then it does something which
triggers request_module().  Say, it can simply call sys_socket().  This
in turn needs more memory and leads to OOM.  oom-killer correctly
chooses T and kills it, but this can't help because it sleeps in
TASK_UNINTERRUPTIBLE and after that oom-killer becomes "disabled" by the
TIF_MEMDIE task T.

Make __request_module() killable.  The only necessary change is that
call_modprobe() should kmalloc argv and module_name, they can't live in
the stack if we use UMH_KILLABLE.  This memory is freed via
call_usermodehelper_freeinfo()->cleanup.

Reported-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Cc: Rusty Russell <rusty@...tcorp.com.au>
Cc: Tejun Heo <tj@...nel.org>
Cc: David Rientjes <rientjes@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/kmod.c |   26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -58,6 +58,12 @@ static DEFINE_SPINLOCK(umh_sysctl_lock);
 */
 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
 
+static void free_modprobe_argv(struct subprocess_info *info)
+{
+	kfree(info->argv[3]); /* check call_modprobe() */
+	kfree(info->argv);
+}
+
 static int call_modprobe(char *module_name, int wait)
 {
 	static char *envp[] = {
@@ -67,10 +73,26 @@ static int call_modprobe(char *module_na
 		NULL
 	};
 
-	char *argv[] = { modprobe_path, "-q", "--", module_name, NULL };
+	char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
+	if (!argv)
+		goto out;
+
+	module_name = kstrdup(module_name, GFP_KERNEL);
+	if (!module_name)
+		goto free_argv;
+
+	argv[0] = modprobe_path;
+	argv[1] = "-q";
+	argv[2] = "--";
+	argv[3] = module_name;	/* check free_modprobe_argv() */
+	argv[4] = NULL;
 
 	return call_usermodehelper_fns(modprobe_path, argv, envp,
-					wait, NULL, NULL, NULL);
+		wait | UMH_KILLABLE, NULL, free_modprobe_argv, NULL);
+free_argv:
+	kfree(argv);
+out:
+	return -ENOMEM;
 }
 
 /**


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