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Subject[PATCH 2/3] proc: Add a way to make network proc files writable
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Date
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>
---

fs/proc/generic.c | 24 ++++++++++++
fs/proc/internal.h | 2 +
fs/proc/proc_net.c | 92 +++++++++++++++++++++++++++++++++++++++++++++++
include/linux/proc_fs.h | 12 ++++++
4 files changed, 130 insertions(+)

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 02bb1914f5f7..d0e5a68ae14a 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -741,3 +741,27 @@ void *PDE_DATA(const struct inode *inode)
return __PDE_DATA(inode);
}
EXPORT_SYMBOL(PDE_DATA);
+
+/*
+ * Pull a user buffer into memory and pass it to the file's write handler if
+ * one is supplied. The ->write() method is permitted to modify the
+ * kernel-side buffer.
+ */
+ssize_t proc_simple_write(struct file *f, const char __user *ubuf, size_t size,
+ loff_t *_pos)
+{
+ struct proc_dir_entry *pde = PDE(file_inode(f));
+ char *buf;
+ int ret;
+
+ if (!pde->write)
+ return -EACCES;
+ if (size == 0 || size > PAGE_SIZE - 1)
+ return -EINVAL;
+ buf = memdup_user_nul(ubuf, size);
+ if (IS_ERR(buf))
+ return PTR_ERR(buf);
+ ret = pde->write(f, buf, size);
+ kfree(buf);
+ return ret == 0 ? size : ret;
+}
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index 6d171485c45b..0f3eeed2767a 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -48,6 +48,7 @@ struct proc_dir_entry {
const struct seq_operations *seq_ops;
int (*single_show)(struct seq_file *, void *);
};
+ proc_write_t write;
unsigned int state_size;
void *data;
unsigned int low_ino;
@@ -187,6 +188,7 @@ static inline bool is_empty_pde(const struct proc_dir_entry *pde)
{
return S_ISDIR(pde->mode) && !pde->proc_iops;
}
+extern ssize_t proc_simple_write(struct file *, const char __user *, size_t, loff_t *);

/*
* inode.c
diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
index baf1994289ce..690764714fc3 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;
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 928c7b2cbff4..33187c55eb8a 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -14,6 +14,8 @@ struct seq_operations;

#ifdef CONFIG_PROC_FS

+typedef int (*proc_write_t)(struct file *, char *, size_t);
+
extern void proc_root_init(void);
extern void proc_flush_task(struct task_struct *);

@@ -61,6 +63,16 @@ struct proc_dir_entry *proc_create_net_data(const char *name, umode_t mode,
struct proc_dir_entry *proc_create_net_single(const char *name, umode_t mode,
struct proc_dir_entry *parent,
int (*show)(struct seq_file *, void *), void *data);
+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 *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);

#else /* CONFIG_PROC_FS */

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