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Date: Sat, 23 Dec 2023 14:04:27 +0100
From: Thomas =?utf-8?Q?Wei=C3=9Fschuh?= <linux@weissschuh.net>
To: Joel Granados <j.granados@samsung.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>, 
	Kees Cook <keescook@chromium.org>, "Gustavo A. R. Silva" <gustavoars@kernel.org>, 
	Iurii Zaikin <yzaikin@google.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, 
	linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v2 13/18] sysctl: move sysctl type to ctl_table_header
Message-ID: <930d06d4-ece0-4b75-b7ce-dba486a0d404@t-8ch.de>
References: <20231204-const-sysctl-v2-0-7a5060b11447@weissschuh.net>
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Hi Joel,

On 2023-12-21 13:09:19+0100, Joel Granados wrote:
> I had some available cycles today and wanted to look at the patch that
> you sent. I could not apply it on top of 6.7-rc6. Have you thought about
> taking this out of your "constification" series and posting it as
> something that comes before the const stuff?

Yes, I am planning to submit this standalone. But I need to do some more
investigation to properly handle the existing comments.

FYI this out-of-series patch is meant to be applied on top of the rest
of the series.


Another question:

When did you write this mail?

The Date header says it's from the 21st but I only received it today
(the 23rd). All other mail headers also say that it was only sent on
23rd. The same seems to happen with your other mails, too.

Thomas

> On Wed, Dec 06, 2023 at 06:53:10AM +0100, Thomas Weißschuh wrote:
> > On 2023-12-05 14:50:01-0800, Luis Chamberlain wrote:
> > > On Tue, Dec 5, 2023 at 2:41 PM Thomas Weißschuh <linux@weissschuh.net> wrote:
> > > >
> > > > On 2023-12-05 14:33:38-0800, Luis Chamberlain wrote:
> > > > > On Mon, Dec 04, 2023 at 08:52:26AM +0100, Thomas Weißschuh wrote:
> > > > > > @@ -231,7 +231,8 @@ static int insert_header(struct ctl_dir *dir, struct ctl_table_header *header)
> > > > > >             return -EROFS;
> > > > > >
> > > > > >     /* Am I creating a permanently empty directory? */
> > > > > > -   if (sysctl_is_perm_empty_ctl_header(header)) {
> > > > > > +   if (header->ctl_table == sysctl_mount_point ||
> > > > > > +       sysctl_is_perm_empty_ctl_header(header)) {
> > > > > >             if (!RB_EMPTY_ROOT(&dir->root))
> > > > > >                     return -EINVAL;
> > > > > >             sysctl_set_perm_empty_ctl_header(dir_h);
> > > > >
> > > > > While you're at it.
> > > >
> > > > This hunk is completely gone in v3/the code that you merged.
> > > 
> > > It is worse in that it is not obvious:
> > > 
> > > +       if (table == sysctl_mount_point)
> > > +               sysctl_set_perm_empty_ctl_header(head);
> > > 
> > > > Which kind of unsafety do you envision here?
> > > 
> > > Making the code obvious during patch review hy this is needed /
> > > special, and if we special case this, why not remove enum, and make it
> > > specific to only that one table. The catch is that it is not
> > > immediately obvious that we actually call
> > > sysctl_set_perm_empty_ctl_header() in other places, and it begs the
> > > question if this can be cleaned up somehow.
> > 
> > Making it specific won't work because the flag needs to be transferred
> > from the leaf table to the table representing the directory.
> > 
> > What do you think of the aproach taken in the attached patch?
> > (On top of current sysctl-next, including my series)
> > 
> > Note: Current sysctl-next ist still based on v6.6.
> 
> > From 2fb9887fb2a5024c2620f2d694bc6dcc32afde67 Mon Sep 17 00:00:00 2001
> > From: =?UTF-8?q?Thomas=20Wei=C3=9Fschuh?= <linux@weissschuh.net>
> > Date: Wed, 6 Dec 2023 06:17:22 +0100
> > Subject: [PATCH] sysctl: simplify handling of permanently empty directories
> > 
> > ---
> >  fs/proc/proc_sysctl.c  | 76 +++++++++++++++++++-----------------------
> >  include/linux/sysctl.h | 13 ++------
> >  2 files changed, 36 insertions(+), 53 deletions(-)
> > 
> > diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> > index c92e9b972ada..c4d6d09b0e68 100644
> > --- a/fs/proc/proc_sysctl.c
> > +++ b/fs/proc/proc_sysctl.c
> > @@ -17,6 +17,7 @@
> >  #include <linux/bpf-cgroup.h>
> >  #include <linux/mount.h>
> >  #include <linux/kmemleak.h>
> > +#include <linux/cleanup.h>
> >  #include "internal.h"
> >  
> >  #define list_for_each_table_entry(entry, header)	\
> > @@ -29,32 +30,6 @@ static const struct inode_operations proc_sys_inode_operations;
> >  static const struct file_operations proc_sys_dir_file_operations;
> >  static const struct inode_operations proc_sys_dir_operations;
> >  
> > -/* Support for permanently empty directories */
> > -static const struct ctl_table sysctl_mount_point[] = {
> > -	{ }
> > -};
> > -
> > -/**
> > - * register_sysctl_mount_point() - registers a sysctl mount point
> > - * @path: path for the mount point
> > - *
> > - * Used to create a permanently empty directory to serve as mount point.
> > - * There are some subtle but important permission checks this allows in the
> > - * case of unprivileged mounts.
> > - */
> > -struct ctl_table_header *register_sysctl_mount_point(const char *path)
> > -{
> > -	return register_sysctl(path, sysctl_mount_point);
> > -}
> > -EXPORT_SYMBOL(register_sysctl_mount_point);
> > -
> > -#define sysctl_is_perm_empty_ctl_header(hptr)		\
> > -	(hptr->type == SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY)
> > -#define sysctl_set_perm_empty_ctl_header(hptr)		\
> > -	(hptr->type = SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY)
> > -#define sysctl_clear_perm_empty_ctl_header(hptr)		\
> > -	(hptr->type = SYSCTL_TABLE_TYPE_DEFAULT)
> > -
> >  void proc_sys_poll_notify(struct ctl_table_poll *poll)
> >  {
> >  	if (!poll)
> > @@ -199,8 +174,6 @@ static void init_header(struct ctl_table_header *head,
> >  	head->set = set;
> >  	head->parent = NULL;
> >  	head->node = node;
> > -	if (table == sysctl_mount_point)
> > -		sysctl_set_perm_empty_ctl_header(head);
> >  	INIT_HLIST_HEAD(&head->inodes);
> >  	if (node) {
> >  		const struct ctl_table *entry;
> > @@ -228,17 +201,9 @@ static int insert_header(struct ctl_dir *dir, struct ctl_table_header *header)
> >  
> >  
> >  	/* Is this a permanently empty directory? */
> > -	if (sysctl_is_perm_empty_ctl_header(dir_h))
> > +	if (dir->permanently_empty)
> >  		return -EROFS;
> >  
> > -	/* Am I creating a permanently empty directory? */
> > -	if (header->ctl_table_size > 0 &&
> > -	    sysctl_is_perm_empty_ctl_header(header)) {
> > -		if (!RB_EMPTY_ROOT(&dir->root))
> > -			return -EINVAL;
> > -		sysctl_set_perm_empty_ctl_header(dir_h);
> > -	}
> > -
> >  	dir_h->nreg++;
> >  	header->parent = dir;
> >  	err = insert_links(header);
> > @@ -254,8 +219,6 @@ static int insert_header(struct ctl_dir *dir, struct ctl_table_header *header)
> >  	erase_header(header);
> >  	put_links(header);
> >  fail_links:
> > -	if (header->ctl_table == sysctl_mount_point)
> > -		sysctl_clear_perm_empty_ctl_header(dir_h);
> >  	header->parent = NULL;
> >  	drop_sysctl_table(dir_h);
> >  	return err;
> > @@ -442,6 +405,7 @@ static struct inode *proc_sys_make_inode(struct super_block *sb,
> >  		struct ctl_table_header *head, const struct ctl_table *table)
> >  {
> >  	struct ctl_table_root *root = head->root;
> > +	struct ctl_dir *ctl_dir;
> >  	struct inode *inode;
> >  	struct proc_inode *ei;
> >  
> > @@ -475,7 +439,9 @@ static struct inode *proc_sys_make_inode(struct super_block *sb,
> >  		inode->i_mode |= S_IFDIR;
> >  		inode->i_op = &proc_sys_dir_operations;
> >  		inode->i_fop = &proc_sys_dir_file_operations;
> > -		if (sysctl_is_perm_empty_ctl_header(head))
> > +
> > +		ctl_dir = container_of(head, struct ctl_dir, header);
> > +		if (ctl_dir->permanently_empty)
> >  			make_empty_dir_inode(inode);
> >  	}
> >  
> > @@ -1214,8 +1180,7 @@ static bool get_links(struct ctl_dir *dir,
> >  	struct ctl_table_header *tmp_head;
> >  	const struct ctl_table *entry, *link;
> >  
> > -	if (header->ctl_table_size == 0 ||
> > -	    sysctl_is_perm_empty_ctl_header(header))
> > +	if (header->ctl_table_size == 0 || dir->permanently_empty)
> >  		return true;
> >  
> >  	/* Are there links available for every entry in table? */
> > @@ -1536,6 +1501,33 @@ void unregister_sysctl_table(struct ctl_table_header * header)
> >  }
> >  EXPORT_SYMBOL(unregister_sysctl_table);
> >  
> > +/**
> > + * register_sysctl_mount_point() - registers a sysctl mount point
> > + * @path: path for the mount point
> > + *
> > + * Used to create a permanently empty directory to serve as mount point.
> > + * There are some subtle but important permission checks this allows in the
> > + * case of unprivileged mounts.
> > + */
> > +struct ctl_table_header *register_sysctl_mount_point(const char *path)
> > +{
> > +	struct ctl_dir *dir = sysctl_mkdir_p(&sysctl_table_root.default_set.dir, path);
> > +
> > +	if (IS_ERR(dir))
> > +		return NULL;
> > +
> > +	guard(spinlock)(&sysctl_lock);
> > +
> > +	if (!RB_EMPTY_ROOT(&dir->root)) {
> > +		drop_sysctl_table(&dir->header);
> > +		return NULL;
> > +	}
> > +
> > +	dir->permanently_empty = true;
> > +	return &dir->header;
> > +}
> > +EXPORT_SYMBOL(register_sysctl_mount_point);
> > +
> >  void setup_sysctl_set(struct ctl_table_set *set,
> >  	struct ctl_table_root *root,
> >  	int (*is_seen)(struct ctl_table_set *))
> > diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
> > index 7c96d5abafc7..329e68d484ed 100644
> > --- a/include/linux/sysctl.h
> > +++ b/include/linux/sysctl.h
> > @@ -177,23 +177,14 @@ struct ctl_table_header {
> >  	struct ctl_dir *parent;
> >  	struct ctl_node *node;
> >  	struct hlist_head inodes; /* head for proc_inode->sysctl_inodes */
> > -	/**
> > -	 * enum type - Enumeration to differentiate between ctl target types
> > -	 * @SYSCTL_TABLE_TYPE_DEFAULT: ctl target with no special considerations
> > -	 * @SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY: Used to identify a permanently
> > -	 *                                       empty directory target to serve
> > -	 *                                       as mount point.
> > -	 */
> > -	enum {
> > -		SYSCTL_TABLE_TYPE_DEFAULT,
> > -		SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY
> > -	} type;
> >  };
> >  
> >  struct ctl_dir {
> >  	/* Header must be at the start of ctl_dir */
> >  	struct ctl_table_header header;
> >  	struct rb_root root;
> > +	/* Permanently empty directory target to serve as mount point. */
> > +	bool permanently_empty;
> >  };
> >  
> >  struct ctl_table_set {
> > 
> > base-commit: a6fd07f80ab7bd94edb4d56c35e61117ffb9957e
> > prerequisite-patch-id: 0000000000000000000000000000000000000000
> > prerequisite-patch-id: 13932e9add940cb65c71e04b5efdfcd3622fd27e
> > prerequisite-patch-id: 2e4d88f7b8aaa805598f0e87a3ea726825bb4264
> > prerequisite-patch-id: 674a680d9cb138cd34cfd0e1a4ec3a5d1c220078
> > prerequisite-patch-id: e27c92582aa20b1dfb122c172b336dbaf9d6508a
> > prerequisite-patch-id: 9b409a34ab6a4d8d8c5225ba9a72db3116e3c8b3
> > prerequisite-patch-id: 86ff15a81d850ebda16bb707491251f4b705e4fd
> > prerequisite-patch-id: b7ab65512ac9acfb2dd482b0271b399467afc56d
> > prerequisite-patch-id: 0354922fbf2508a89f3e9d9a4e274fc98deb2e93
> > prerequisite-patch-id: b71389e82026ffc19cbb717bba1a014ad6cab6da
> > prerequisite-patch-id: fbb0201f89bf6c41d0585af867bdeec8d51649b2
> > prerequisite-patch-id: e3b4b5b69b4eadf87ed97beb8c03a471e7628cb9
> > prerequisite-patch-id: 3fbc9745cf3f28872b3e63f6d1f6e2fd7598be8a
> > prerequisite-patch-id: ba2b190c2e54cfb505a282e688c2222712f0acd7
> > prerequisite-patch-id: 47e5ca730748bb7bf9248a9e711045d8c1028199
> > prerequisite-patch-id: dcd9f87f00290d2f9be83e404f8883eb90c5fb1c
> > prerequisite-patch-id: d4629be1a61585ab821da2d2850f246761f72f25
> > prerequisite-patch-id: f740190f4b94e57cbf3659f220d94483713341a1
> > prerequisite-patch-id: 301c2e530e2af4568267e19247d4a49ac2a9871d
> > -- 
> > 2.43.0
> > 
> 
> 
> -- 
> 
> Joel Granados