Allow to change a /proc/cmdline by a root user (writable /proc/cmdline)


diff -urN linux-2.6.32-fan32d-r10303.x86_64.old/fs/proc/cmdline.c linux-2.6.32-fan32d-r10303.x86_64/fs/proc/cmdline.c
--- linux-2.6.32-fan32d-r10303.x86_64.old/fs/proc/cmdline.c	2014-12-29 23:30:31.000000000 +0300
+++ linux-2.6.32-fan32d-r10303.x86_64/fs/proc/cmdline.c	2014-12-30 15:26:23.000000000 +0300
@@ -3,6 +3,7 @@
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
 #include <linux/sched.h>
+#include <asm/uaccess.h>
 
 static int cmdline_proc_show(struct seq_file *m, void *v)
 {
@@ -24,16 +25,54 @@
 	return single_open(file, cmdline_proc_show, NULL);
 }
 
+static ssize_t cmdline_proc_write(struct file *file, const char __user *buf,
+				   size_t count, loff_t *ppos)
+{
+	struct ve_struct *ve = get_exec_env();
+	char *cmdline;
+
+	if (count > PAGE_SIZE - 1)
+ 		count = PAGE_SIZE - 1;
+
+	cmdline = kzalloc(count + 1, GFP_KERNEL);
+	if (unlikely(!cmdline))
+		return -ENOMEM;
+
+	if (copy_from_user(cmdline, buf, count)) {
+		kfree(cmdline);
+		return -EFAULT;
+	}
+
+	if (!ve_is_super(ve))	{
+		if (ve->proc_cmdline) {
+			kfree(ve->proc_cmdline);
+			ve->proc_cmdline = 0;
+		}
+		ve->proc_cmdline = cmdline;
+	}
+	else {
+		static was_here = 0;
+		if (was_here)
+		    kfree(saved_command_line);
+
+		was_here = 1;
+		saved_command_line = cmdline;
+	}
+
+	return count;
+}
+
 static const struct file_operations cmdline_proc_fops = {
 	.open		= cmdline_proc_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
 	.release	= single_release,
+	.write		= cmdline_proc_write,
 };
 
 static int __init proc_cmdline_init(void)
 {
-	proc_create("cmdline", 0, &glob_proc_root, &cmdline_proc_fops);
+	proc_create("cmdline", S_IRUGO|S_IWUSR, &glob_proc_root, &cmdline_proc_fops);
 	return 0;
 }
 module_init(proc_cmdline_init);