proc: Add a way to make network proc files writable

Provide two extra functions, proc_create_net_data_write() and
proc_create_net_single_write() that act like their non-write versions but
also set a write method in the proc_dir_entry struct.

An internal simple write function is provided that will copy its buffer and
hand it to the pde->write() method if available (or give an error if not).
The buffer may be modified by the write method.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 92 insertions, 0 deletions

diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
index 7d94fa005b0d..d5e0fcb3439e 100644
--- a/fs/proc/proc_net.c
+++ b/fs/proc/proc_net.c
@@ -46,6 +46,9 @@ static int seq_open_net(struct inode *inode, struct file *file)
 
 	WARN_ON_ONCE(state_size < sizeof(*p));
 
+	if (file->f_mode & FMODE_WRITE && !PDE(inode)->write)
+		return -EACCES;
+
 	net = get_proc_net(inode);
 	if (!net)
 		return -ENXIO;
@@ -73,6 +76,7 @@ static int seq_release_net(struct inode *ino, struct file *f)
 static const struct file_operations proc_net_seq_fops = {
 	.open		= seq_open_net,
 	.read		= seq_read,
+	.write		= proc_simple_write,
 	.llseek		= seq_lseek,
 	.release	= seq_release_net,
 };
@@ -93,6 +97,50 @@ struct proc_dir_entry *proc_create_net_data(const char *name, umode_t mode,
 }
 EXPORT_SYMBOL_GPL(proc_create_net_data);
 
+/**
+ * proc_create_net_data_write - Create a writable net_ns-specific proc file
+ * @name: The name of the file.
+ * @mode: The file's access mode.
+ * @parent: The parent directory in which to create.
+ * @ops: The seq_file ops with which to read the file.
+ * @write: The write method which which to 'modify' the file.
+ * @data: Data for retrieval by PDE_DATA().
+ *
+ * Create a network namespaced proc file in the @parent directory with the
+ * specified @name and @mode that allows reading of a file that displays a
+ * series of elements and also provides for the file accepting writes that have
+ * some arbitrary effect.
+ *
+ * The functions in the @ops table are used to iterate over items to be
+ * presented and extract the readable content using the seq_file interface.
+ *
+ * The @write function is called with the data copied into a kernel space
+ * scratch buffer and has a NUL appended for convenience.  The buffer may be
+ * modified by the @write function.  @write should return 0 on success.
+ *
+ * The @data value is accessible from the @show and @write functions by calling
+ * PDE_DATA() on the file inode.  The network namespace must be accessed by
+ * calling seq_file_net() on the seq_file struct.
+ */
+struct proc_dir_entry *proc_create_net_data_write(const char *name, umode_t mode,
+						  struct proc_dir_entry *parent,
+						  const struct seq_operations *ops,
+						  proc_write_t write,
+						  unsigned int state_size, void *data)
+{
+	struct proc_dir_entry *p;
+
+	p = proc_create_reg(name, mode, &parent, data);
+	if (!p)
+		return NULL;
+	p->proc_fops = &proc_net_seq_fops;
+	p->seq_ops = ops;
+	p->state_size = state_size;
+	p->write = write;
+	return proc_register(parent, p);
+}
+EXPORT_SYMBOL_GPL(proc_create_net_data_write);
+
 static int single_open_net(struct inode *inode, struct file *file)
 {
 	struct proc_dir_entry *de = PDE(inode);
@@ -119,6 +167,7 @@ static int single_release_net(struct inode *ino, struct file *f)
 static const struct file_operations proc_net_single_fops = {
 	.open		= single_open_net,
 	.read		= seq_read,
+	.write		= proc_simple_write,
 	.llseek		= seq_lseek,
 	.release	= single_release_net,
 };
@@ -138,6 +187,49 @@ struct proc_dir_entry *proc_create_net_single(const char *name, umode_t mode,
 }
 EXPORT_SYMBOL_GPL(proc_create_net_single);
 
+/**
+ * proc_create_net_single_write - Create a writable net_ns-specific proc file
+ * @name: The name of the file.
+ * @mode: The file's access mode.
+ * @parent: The parent directory in which to create.
+ * @show: The seqfile show method with which to read the file.
+ * @write: The write method which which to 'modify' the file.
+ * @data: Data for retrieval by PDE_DATA().
+ *
+ * Create a network-namespaced proc file in the @parent directory with the
+ * specified @name and @mode that allows reading of a file that displays a
+ * single element rather than a series and also provides for the file accepting
+ * writes that have some arbitrary effect.
+ *
+ * The @show function is called to extract the readable content via the
+ * seq_file interface.
+ *
+ * The @write function is called with the data copied into a kernel space
+ * scratch buffer and has a NUL appended for convenience.  The buffer may be
+ * modified by the @write function.  @write should return 0 on success.
+ *
+ * The @data value is accessible from the @show and @write functions by calling
+ * PDE_DATA() on the file inode.  The network namespace must be accessed by
+ * calling seq_file_single_net() on the seq_file struct.
+ */
+struct proc_dir_entry *proc_create_net_single_write(const char *name, umode_t mode,
+						    struct proc_dir_entry *parent,
+						    int (*show)(struct seq_file *, void *),
+						    proc_write_t write,
+						    void *data)
+{
+	struct proc_dir_entry *p;
+
+	p = proc_create_reg(name, mode, &parent, data);
+	if (!p)
+		return NULL;
+	p->proc_fops = &proc_net_single_fops;
+	p->single_show = show;
+	p->write = write;
+	return proc_register(parent, p);
+}
+EXPORT_SYMBOL_GPL(proc_create_net_single_write);
+
 static struct net *get_proc_task_net(struct inode *dir)
 {
 	struct task_struct *task;