proc: Make inline name size calculation automatic

Make calculation of the size of the inline name in struct proc_dir_entry
automatic, rather than having to manually encode the numbers and failing to
allow for lockdep.

Require a minimum inline name size of 33+1 to allow for names that look
like two hex numbers with a dash between.

Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/proc/generic.c

@@ -410,7 +410,7 @@ static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
 	if (!ent)
 		goto out;
 
-	if (qstr.len + 1 <= sizeof(ent->inline_name)) {
+	if (qstr.len + 1 <= SIZEOF_PDE_INLINE_NAME) {
 		ent->name = ent->inline_name;
 	} else {
 		ent->name = kmalloc(qstr.len + 1, GFP_KERNEL);

fs/proc/inode.c

@@ -105,9 +105,8 @@ void __init proc_init_kmemcache(void)
 		kmem_cache_create("pde_opener", sizeof(struct pde_opener), 0,
 				  SLAB_ACCOUNT|SLAB_PANIC, NULL);
 	proc_dir_entry_cache = kmem_cache_create_usercopy(
-		"proc_dir_entry", sizeof(struct proc_dir_entry), 0, SLAB_PANIC,
-		offsetof(struct proc_dir_entry, inline_name),
-		sizeof_field(struct proc_dir_entry, inline_name), NULL);
+		"proc_dir_entry", SIZEOF_PDE_SLOT, 0, SLAB_PANIC,
+		OFFSETOF_PDE_NAME, SIZEOF_PDE_INLINE_NAME, NULL);
 }
 
 static int proc_show_options(struct seq_file *seq, struct dentry *root)

fs/proc/internal.h

@@ -62,14 +62,20 @@ struct proc_dir_entry {
 	char *name;
 	umode_t mode;
 	u8 namelen;
-#ifdef CONFIG_64BIT
-#define SIZEOF_PDE_INLINE_NAME	(192-155)
-#else
-#define SIZEOF_PDE_INLINE_NAME	(128-95)
-#endif
-	char inline_name[SIZEOF_PDE_INLINE_NAME];
+	char inline_name[];
 } __randomize_layout;
 
+#define OFFSETOF_PDE_NAME offsetof(struct proc_dir_entry, inline_name)
+#define SIZEOF_PDE_SLOT					\
+	(OFFSETOF_PDE_NAME + 34 <= 64 ? 64 :		\
+	 OFFSETOF_PDE_NAME + 34 <= 128 ? 128 :		\
+	 OFFSETOF_PDE_NAME + 34 <= 192 ? 192 :		\
+	 OFFSETOF_PDE_NAME + 34 <= 256 ? 256 :		\
+	 OFFSETOF_PDE_NAME + 34 <= 512 ? 512 :		\
+	 0)
+
+#define SIZEOF_PDE_INLINE_NAME (SIZEOF_PDE_SLOT - OFFSETOF_PDE_NAME)
+
 extern struct kmem_cache *proc_dir_entry_cache;
 void pde_free(struct proc_dir_entry *pde);
 

fs/proc/root.c

@@ -204,8 +204,7 @@ struct proc_dir_entry proc_root = {
 	.proc_fops	= &proc_root_operations,
 	.parent		= &proc_root,
 	.subdir		= RB_ROOT,
-	.name		= proc_root.inline_name,
-	.inline_name	= "/proc",
+	.name		= "/proc",
 };
 
 int pid_ns_prepare_proc(struct pid_namespace *ns)