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Date: Mon, 15 Apr 2024 20:23:43 +0300
From: Alexey Dobriyan <adobriyan@gmail.com>
To: Luis Chamberlain <mcgrof@kernel.org>
Cc: akpm@linux-foundation.org, linux-modules@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz
Subject: Re: [PATCH] module: ban '.', '..' as module names, ban '/' in module
 names
Message-ID: <e770923a-6719-403c-a9f2-1f7ac4313474@p183>
References: <ee371cf7-69fa-4f9c-99b9-59bab86f25e4@p183>
 <ZhxDj3vQFLy62Yow@bombadil.infradead.org>
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In-Reply-To: <ZhxDj3vQFLy62Yow@bombadil.infradead.org>

On Sun, Apr 14, 2024 at 01:58:55PM -0700, Luis Chamberlain wrote:
> On Sun, Apr 14, 2024 at 10:05:05PM +0300, Alexey Dobriyan wrote:
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -3616,4 +3616,12 @@ extern int vfs_fadvise(struct file *file, loff_t offset, loff_t len,
> >  extern int generic_fadvise(struct file *file, loff_t offset, loff_t len,
> >  			   int advice);
> >  
> > +/*
> > + * Use this if data from userspace end up as directory/filename on
> > + * some virtual filesystem.
> > + */
> > +static inline bool string_is_vfs_ready(const char *s)
> > +{
> > +	return strcmp(s, ".") != 0 && strcmp(s, "..") != 0 && !strchr(s, '/');
> > +}
> >  #endif /* _LINUX_FS_H */
> > --- a/kernel/module/main.c
> > +++ b/kernel/module/main.c
> > @@ -2893,6 +2893,11 @@ static int load_module(struct load_info *info, const char __user *uargs,
> >  
> >  	audit_log_kern_module(mod->name);
> >  
> > +	if (!string_is_vfs_ready(mod->name)) {
> > +		err = -EINVAL;
> > +		goto free_module;
> > +	}
> > +
> 
> Sensible change however to put string_is_vfs_ready() in include/linux/fs.h 
> is a stretch if there really are no other users.

This is forward thinking patch :-)

Other subsystems may create files/directories in proc/sysfs, and should
check for bad names as well:

	/proc/2821/net/dev_snmp6/eth0

This looks exactly like something coming from userspace and making it
into /proc, so the filter function doesn't belong to kernel/module/internal.h