proc: fix ->open'less usage due to ->proc_fops flip

Typical PDE creation code looks like:

	pde = create_proc_entry("foo", 0, NULL);
	if (pde)
		pde->proc_fops = &foo_proc_fops;

Notice that PDE is first created, only then ->proc_fops is set up to
final value. This is a problem because right after creation
a) PDE is fully visible in /proc , and
b) ->proc_fops are proc_file_operations which do not have ->open callback. So, it's
   possible to ->read without ->open (see one class of oopses below).

The fix is new API called proc_create() which makes sure ->proc_fops are
set up before gluing PDE to main tree. Typical new code looks like:

	pde = proc_create("foo", 0, NULL, &foo_proc_fops);
	if (!pde)
		return -ENOMEM;

Fix most networking users for a start.

In the long run, create_proc_entry() for regular files will go.

BUG: unable to handle kernel NULL pointer dereference at virtual address 00000024
printing eip: c1188c1b *pdpt = 000000002929e001 *pde = 0000000000000000
Oops: 0002 [#1] PREEMPT SMP DEBUG_PAGEALLOC
last sysfs file: /sys/block/sda/sda1/dev
Modules linked in: foo af_packet ipv6 cpufreq_ondemand loop serio_raw psmouse k8temp hwmon sr_mod cdrom

Pid: 24679, comm: cat Not tainted (2.6.24-rc3-mm1 #2)
EIP: 0060:[<c1188c1b>] EFLAGS: 00210002 CPU: 0
EIP is at mutex_lock_nested+0x75/0x25d
EAX: 000006fe EBX: fffffffb ECX: 00001000 EDX: e9340570
ESI: 00000020 EDI: 00200246 EBP: e9340570 ESP: e8ea1ef8
 DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
Process cat (pid: 24679, ti=E8EA1000 task=E9340570 task.ti=E8EA1000)
Stack: 00000000 c106f7ce e8ee05b4 00000000 00000001 458003d0 f6fb6f20 fffffffb
       00000000 c106f7aa 00001000 c106f7ce 08ae9000 f6db53f0 00000020 00200246
       00000000 00000002 00000000 00200246 00200246 e8ee05a0 fffffffb e8ee0550
Call Trace:
 [<c106f7ce>] seq_read+0x24/0x28a
 [<c106f7aa>] seq_read+0x0/0x28a
 [<c106f7ce>] seq_read+0x24/0x28a
 [<c106f7aa>] seq_read+0x0/0x28a
 [<c10818b8>] proc_reg_read+0x60/0x73
 [<c1081858>] proc_reg_read+0x0/0x73
 [<c105a34f>] vfs_read+0x6c/0x8b
 [<c105a6f3>] sys_read+0x3c/0x63
 [<c10025f2>] sysenter_past_esp+0x5f/0xa5
 [<c10697a7>] destroy_inode+0x24/0x33
 =======================
INFO: lockdep is turned off.
Code: 75 21 68 e1 1a 19 c1 68 87 00 00 00 68 b8 e8 1f c1 68 25 73 1f c1 e8 84 06 e9 ff e8 52 b8 e7 ff 83 c4 10 9c 5f fa e8 28 89 ea ff <f0> fe 4e 04 79 0a f3 90 80 7e 04 00 7e f8 eb f0 39 76 34 74 33
EIP: [<c1188c1b>] mutex_lock_nested+0x75/0x25d SS:ESP 0068:e8ea1ef8

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/generic.c

@@ -562,7 +562,7 @@ static int proc_register(struct proc_dir_entry * dir, struct proc_dir_entry * dp
 	return 0;
 }
 
-static struct proc_dir_entry *proc_create(struct proc_dir_entry **parent,
+static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
 					  const char *name,
 					  mode_t mode,
 					  nlink_t nlink)
@@ -605,7 +605,7 @@ struct proc_dir_entry *proc_symlink(const char *name,
 {
 	struct proc_dir_entry *ent;
 
-	ent = proc_create(&parent,name,
+	ent = __proc_create(&parent, name,
 			  (S_IFLNK | S_IRUGO | S_IWUGO | S_IXUGO),1);
 
 	if (ent) {
@@ -630,7 +630,7 @@ struct proc_dir_entry *proc_mkdir_mode(const char *name, mode_t mode,
 {
 	struct proc_dir_entry *ent;
 
-	ent = proc_create(&parent, name, S_IFDIR | mode, 2);
+	ent = __proc_create(&parent, name, S_IFDIR | mode, 2);
 	if (ent) {
 		if (proc_register(parent, ent) < 0) {
 			kfree(ent);
@@ -664,7 +664,7 @@ struct proc_dir_entry *create_proc_entry(const char *name, mode_t mode,
 		nlink = 1;
 	}
 
-	ent = proc_create(&parent,name,mode,nlink);
+	ent = __proc_create(&parent, name, mode, nlink);
 	if (ent) {
 		if (proc_register(parent, ent) < 0) {
 			kfree(ent);
@@ -674,6 +674,38 @@ struct proc_dir_entry *create_proc_entry(const char *name, mode_t mode,
 	return ent;
 }
 
+struct proc_dir_entry *proc_create(const char *name, mode_t mode,
+				   struct proc_dir_entry *parent,
+				   const struct file_operations *proc_fops)
+{
+	struct proc_dir_entry *pde;
+	nlink_t nlink;
+
+	if (S_ISDIR(mode)) {
+		if ((mode & S_IALLUGO) == 0)
+			mode |= S_IRUGO | S_IXUGO;
+		nlink = 2;
+	} else {
+		if ((mode & S_IFMT) == 0)
+			mode |= S_IFREG;
+		if ((mode & S_IALLUGO) == 0)
+			mode |= S_IRUGO;
+		nlink = 1;
+	}
+
+	pde = __proc_create(&parent, name, mode, nlink);
+	if (!pde)
+		goto out;
+	pde->proc_fops = proc_fops;
+	if (proc_register(parent, pde) < 0)
+		goto out_free;
+	return pde;
+out_free:
+	kfree(pde);
+out:
+	return NULL;
+}
+
 void free_proc_entry(struct proc_dir_entry *de)
 {
 	unsigned int ino = de->low_ino;

fs/proc/proc_net.c

@@ -67,12 +67,7 @@ EXPORT_SYMBOL_GPL(seq_release_net);
 struct proc_dir_entry *proc_net_fops_create(struct net *net,
 	const char *name, mode_t mode, const struct file_operations *fops)
 {
-	struct proc_dir_entry *res;
-
-	res = create_proc_entry(name, mode, net->proc_net);
-	if (res)
-		res->proc_fops = fops;
-	return res;
+	return proc_create(name, mode, net->proc_net, fops);
 }
 EXPORT_SYMBOL_GPL(proc_net_fops_create);
 

fs/proc/root.c

@@ -232,6 +232,7 @@ void pid_ns_release_proc(struct pid_namespace *ns)
 EXPORT_SYMBOL(proc_symlink);
 EXPORT_SYMBOL(proc_mkdir);
 EXPORT_SYMBOL(create_proc_entry);
+EXPORT_SYMBOL(proc_create);
 EXPORT_SYMBOL(remove_proc_entry);
 EXPORT_SYMBOL(proc_root);
 EXPORT_SYMBOL(proc_root_fs);

include/linux/proc_fs.h

@@ -126,6 +126,9 @@ void de_put(struct proc_dir_entry *de);
 
 extern struct proc_dir_entry *create_proc_entry(const char *name, mode_t mode,
 						struct proc_dir_entry *parent);
+struct proc_dir_entry *proc_create(const char *name, mode_t mode,
+				struct proc_dir_entry *parent,
+				const struct file_operations *proc_fops);
 extern void remove_proc_entry(const char *name, struct proc_dir_entry *parent);
 
 extern struct vfsmount *proc_mnt;
@@ -220,7 +223,12 @@ static inline void proc_flush_task(struct task_struct *task)
 
 static inline struct proc_dir_entry *create_proc_entry(const char *name,
 	mode_t mode, struct proc_dir_entry *parent) { return NULL; }
-
+static inline struct proc_dir_entry *proc_create(const char *name,
+	mode_t mode, struct proc_dir_entry *parent,
+	const struct file_operations *proc_fops)
+{
+	return NULL;
+}
 #define remove_proc_entry(name, parent) do {} while (0)
 
 static inline struct proc_dir_entry *proc_symlink(const char *name,