[PATCH -vfs] proc: don't maintain sizeof(struct proc_dir_entry)

[PATCH -vfs] proc: don't maintain sizeof(struct proc_dir_entry)

[Alexey Dobriyan]

Automatically cap sizeof(struct proc_dir_entry) at 192/128 bytes or
256/192 bytes if spinlock debugging/lockdep is enabled.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 fs/proc/generic.c  |    2 +-
 fs/proc/inode.c    |    5 +++--
 fs/proc/internal.h |   10 ++++++----
 3 files changed, 10 insertions(+), 7 deletions(-)

--- a/fs/proc/generic.c
+++ b/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);
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -105,9 +105,10 @@ 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,
+		"proc_dir_entry", SIZEOF_PDE, 0, SLAB_PANIC,
 		offsetof(struct proc_dir_entry, inline_name),
-		sizeof_field(struct proc_dir_entry, inline_name), NULL);
+		SIZEOF_PDE_INLINE_NAME, NULL);
+	BUILD_BUG_ON(sizeof(struct proc_dir_entry) >= SIZEOF_PDE);
 }
 
 static int proc_show_options(struct seq_file *seq, struct dentry *root)
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -61,13 +61,15 @@ struct proc_dir_entry {
 	char *name;
 	umode_t mode;
 	u8 namelen;
+	char inline_name[];
+} __randomize_layout;
+
 #ifdef CONFIG_64BIT
-#define SIZEOF_PDE_INLINE_NAME	(192-155)
+#define SIZEOF_PDE	(sizeof(spinlock_t) == 4 ? 192 : 256)
 #else
-#define SIZEOF_PDE_INLINE_NAME	(128-95)
+#define SIZEOF_PDE	(sizeof(spinlock_t) == 4 ? 128 : 192)
 #endif
-	char inline_name[SIZEOF_PDE_INLINE_NAME];
-} __randomize_layout;
+#define SIZEOF_PDE_INLINE_NAME	(SIZEOF_PDE - sizeof(struct proc_dir_entry))
 
 extern struct kmem_cache *proc_dir_entry_cache;
 void pde_free(struct proc_dir_entry *pde);

Re: [PATCH -vfs] proc: don't maintain sizeof(struct proc_dir_entry)

[Al Viro]

On Fri, May 18, 2018 at 11:02:13PM +0300, Alexey Dobriyan wrote:
> Automatically cap sizeof(struct proc_dir_entry) at 192/128 bytes or
> 256/192 bytes if spinlock debugging/lockdep is enabled.

> --- a/fs/proc/internal.h
> +++ b/fs/proc/internal.h
> @@ -61,13 +61,15 @@ struct proc_dir_entry {
>  	char *name;
>  	umode_t mode;
>  	u8 namelen;
> +	char inline_name[];
> +} __randomize_layout;
> +

Hmm...  proc_root initialization relies upon a gccism after that...
Speaking of which, why the hell do we even bother with proc_root.name?

Re: [PATCH -vfs] proc: don't maintain sizeof(struct proc_dir_entry)

[Alexey Dobriyan]

On Fri, May 18, 2018 at 09:23:15PM +0100, Al Viro wrote:
> On Fri, May 18, 2018 at 11:02:13PM +0300, Alexey Dobriyan wrote:
> > Automatically cap sizeof(struct proc_dir_entry) at 192/128 bytes or
> > 256/192 bytes if spinlock debugging/lockdep is enabled.
> 
> > --- a/fs/proc/internal.h
> > +++ b/fs/proc/internal.h
> > @@ -61,13 +61,15 @@ struct proc_dir_entry {
> >  	char *name;
> >  	umode_t mode;
> >  	u8 namelen;
> > +	char inline_name[];
> > +} __randomize_layout;
> > +
> 
> Hmm...  proc_root initialization relies upon a gccism after that...

Yeah well.

> Speaking of which, why the hell do we even bother with proc_root.name?

printk("%s/%s", pde->parent->name, pde->name) is nice and doesn't cost
anything (OK, it may cost 5 bytes).