linux-kernel - Re: [PATCH RFC v10 6/17] security: add new securityfs delete function

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Date:   Fri, 14 Jul 2023 16:59:01 -0700
From:   Fan Wu <wufan@...ux.microsoft.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     corbet@....net, zohar@...ux.ibm.com, jmorris@...ei.org,
        serge@...lyn.com, tytso@....edu, ebiggers@...nel.org,
        axboe@...nel.dk, agk@...hat.com, snitzer@...nel.org,
        eparis@...hat.com, linux-doc@...r.kernel.org,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-fscrypt@...r.kernel.org, linux-block@...r.kernel.org,
        dm-devel@...hat.com, audit@...r.kernel.org,
        roberto.sassu@...wei.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v10 6/17] security: add new securityfs delete function

On Sat, Jul 08, 2023 at 12:23:03AM -0400, Paul Moore wrote:
> On Jun 28, 2023 Fan Wu <wufan@...ux.microsoft.com> wrote:
> > 
> > When deleting a directory in the security file system, the existing
> > securityfs_remove requires the directory to be empty, otherwise
> > it will do nothing. This leads to a potential risk that the security
> > file system might be in an unclean state when the intentded deletion
> > did not happen.
> > 
> > This commit introduces a new function securityfs_recursive_remove
> > to recursively delete a directory without leaving an unclean state.
> > 
> > Co-developed-by: "Christian Brauner (Microsoft)" <brauner@...nel.org>
> > Signed-off-by: Fan Wu <wufan@...ux.microsoft.com>
> > ---
> >  include/linux/security.h |  1 +
> >  security/inode.c         | 25 +++++++++++++++++++++++++
> >  2 files changed, 26 insertions(+)
> > 
> > diff --git a/include/linux/security.h b/include/linux/security.h
> > index e2734e9e44d5..a88076ebc7b1 100644
> > --- a/include/linux/security.h
> > +++ b/include/linux/security.h
> > @@ -1971,6 +1971,7 @@ struct dentry *securityfs_create_symlink(const char *name,
> >  					 const char *target,
> >  					 const struct inode_operations *iops);
> >  extern void securityfs_remove(struct dentry *dentry);
> > +extern void securityfs_recursive_remove(struct dentry *dentry);
> >  
> >  #else /* CONFIG_SECURITYFS */
> >  
> > diff --git a/security/inode.c b/security/inode.c
> > index 6c326939750d..13358e8547e8 100644
> > --- a/security/inode.c
> > +++ b/security/inode.c
> > @@ -313,6 +313,31 @@ void securityfs_remove(struct dentry *dentry)
> >  }
> >  EXPORT_SYMBOL_GPL(securityfs_remove);
> >  
> > +static void remove_one(struct dentry *victim)
> > +{
> > +	simple_release_fs(&mount, &mount_count);
> > +}
> > +
> > +/**
> > + * securityfs_recursive_remove - recursively removes a file or directory from the securityfs filesystem
> 
> I really want to see lines less than or equal to 80 characters; I
> would suggest this:
> 
> "securityfs_recursive_remove - recursively removes a file or directory"
> 
Thanks for the suggestion, I will make the change accordingly.

-Fan
> > + * @dentry: a pointer to a the dentry of the file or directory to be removed.
> > + *
> > + * This function recursively removes a file or directory in securityfs that was
> > + * previously created with a call to another securityfs function (like
> > + * securityfs_create_file() or variants thereof.)
> > + */
> > +void securityfs_recursive_remove(struct dentry *dentry)
> > +{
> > +	if (IS_ERR_OR_NULL(dentry))
> > +		return;
> > +
> > +	simple_pin_fs(&fs_type, &mount, &mount_count);
> > +	simple_recursive_removal(dentry, remove_one);
> > +	simple_release_fs(&mount, &mount_count);
> > +}
> > +EXPORT_SYMBOL_GPL(securityfs_recursive_remove);
> > +
> >  #ifdef CONFIG_SECURITY
> >  static struct dentry *lsm_dentry;
> >  static ssize_t lsm_read(struct file *filp, char __user *buf, size_t count,
> > -- 
> > 2.25.1
> 
> --
> paul-moore.com