linux-kernel - Re: [PATCH v2 2/3] sysfs: Only accept read/write permissions for file attributes

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Date:	Thu, 12 Mar 2015 14:49:25 +0100
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
	linux-kernel@...r.kernel.org, kernel@...oirfairelinux.com
Subject: Re: [PATCH v2 2/3] sysfs: Only accept read/write permissions for
 file attributes

On Thu, Mar 12, 2015 at 03:39:04AM -0700, Guenter Roeck wrote:
> On 03/12/2015 03:01 AM, Greg Kroah-Hartman wrote:
> >On Wed, Mar 11, 2015 at 02:22:10PM -0400, Vivien Didelot wrote:
> >>For sysfs file attributes, only read and write permissions make sense.
> >>Mask provided attribute permissions accordingly and send a warning
> >>to the console if invalid permission bits are set.
> >>
> >>This patch is originally from Guenter [1] and includes the fixup
> >>explained in the thread, that is printing permissions in octal format
> >>and limiting the scope of attributes to SYSFS_PREALLOC | 0664.
> >>
> >>[1] https://lkml.org/lkml/2015/1/19/599
> >>
> >>Cc: Guenter Roeck <linux@...ck-us.net>
> >>Signed-off-by: Vivien Didelot <vivien.didelot@...oirfairelinux.com>
> >>---
> >>  fs/sysfs/group.c | 6 ++++++
> >>  1 file changed, 6 insertions(+)
> >>
> >>diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
> >>index 3fdccd9..b400c04 100644
> >>--- a/fs/sysfs/group.c
> >>+++ b/fs/sysfs/group.c
> >>@@ -55,6 +55,12 @@ static int create_files(struct kernfs_node *parent, struct kobject *kobj,
> >>  				if (!mode)
> >>  					continue;
> >>  			}
> >>+
> >>+			WARN(mode & ~(SYSFS_PREALLOC | 0664),
> >>+			     "Attribute %s: Invalid permissions 0%o\n",
> >>+			     (*attr)->name, mode);
> >>+
> >>+			mode &= SYSFS_PREALLOC | 0664;
> >
> >How does a "normal" boot look with this warning in place?  There still
> >seem to be a number of files in sysfs that might trigger this.
> >
> I was under the impression that they all were addressed, but I may have
> missed some pattern(s). Can you point me to an example, by any chance ?

Ah, nevermind, they seem to have all been fixed up.

> >Also, we have a build-time warning if a sysfs file is this type of
> >attribute, shouldn't we just rely on that instead of this run-time
> >warning?
> >
> 
> The mode value can be returned from an is_visible function, and even if not
> there is no guarantee that the build-time warning triggers (attribute lists
> can be generated manually, for example).

You are correct, sorry, I missed that, nevermind again.  Once Vivien
fixes up the signed-off-by stuff here, I'll be glad to queue them up.

thanks,

greg k-h
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