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SubjectRe: [patch 00/13] devtmpfs patches
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On Wed, 2009-05-13 at 10:35 -0400, Stephen Smalley wrote:
> > Maybe we could do the same credential swap in sysfs, and get rid of:
> > /**
> > * lookup_one_noperm - bad hack for sysfs
> >
> > Seems a bit odd to have a vfs function for a single filesystem, called
> > from a single location, and annotated as "do not use". Christoph added
> > the comment a while ago, so adding him to Cc:.
>
> Yes, that makes sense to me as well - we didn't have the credentials
> infrastructure in place at the time that lookup_one_noperm was
> introduced, but switching the credentials around a normal lookup_one_len
> call should work now.

Something like this? It seems to work fine here, but I did not test it with SELinux.

Thanks,
Kay


From: Kay Sievers <kay.sievers@vrfy.org>
Subject: sysfs - switch noperm lookup_one_len() hack to credentials switch
Cc: Greg KH <greg@kroah.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: David Howells <dhowells@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>

Driver core actions may be requested by processes, which do not have the
proper permissions in a DAC and LSM/SELinux context to create entries in
sysfs. This replaces the vfs noperm hack with a switch to init_cred before
sysfs entries are created.

Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
---
fs/namei.c | 22 ----------------------
fs/sysfs/dir.c | 7 ++++++-
include/linux/namei.h | 1 -
3 files changed, 6 insertions(+), 24 deletions(-)

--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1260,28 +1260,6 @@ struct dentry *lookup_one_len(const char
return __lookup_hash(&this, base, NULL);
}

-/**
- * lookup_one_noperm - bad hack for sysfs
- * @name: pathname component to lookup
- * @base: base directory to lookup from
- *
- * This is a variant of lookup_one_len that doesn't perform any permission
- * checks. It's a horrible hack to work around the braindead sysfs
- * architecture and should not be used anywhere else.
- *
- * DON'T USE THIS FUNCTION EVER, thanks.
- */
-struct dentry *lookup_one_noperm(const char *name, struct dentry *base)
-{
- int err;
- struct qstr this;
-
- err = __lookup_one_len(name, &this, base, strlen(name));
- if (err)
- return ERR_PTR(err);
- return __lookup_hash(&this, base, NULL);
-}
-
int user_path_at(int dfd, const char __user *name, unsigned flags,
struct path *path)
{
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -21,6 +21,8 @@
#include <linux/completion.h>
#include <linux/mutex.h>
#include <linux/slab.h>
+#include <linux/cred.h>
+#include <linux/init_task.h>
#include "sysfs.h"

DEFINE_MUTEX(sysfs_mutex);
@@ -103,6 +105,7 @@ struct dentry *sysfs_get_dentry(struct s

while (dentry->d_fsdata != sd) {
struct sysfs_dirent *cur;
+ const struct cred *curr_cred;
struct dentry *parent;

/* find the first ancestor which hasn't been looked up */
@@ -111,11 +114,13 @@ struct dentry *sysfs_get_dentry(struct s
cur = cur->s_parent;

/* look it up */
+ curr_cred = override_creds(&init_cred);
parent = dentry;
mutex_lock(&parent->d_inode->i_mutex);
- dentry = lookup_one_noperm(cur->s_name, parent);
+ dentry = lookup_one_len(cur->s_name, parent, strlen(cur->s_name));
mutex_unlock(&parent->d_inode->i_mutex);
dput(parent);
+ revert_creds(curr_cred);

if (IS_ERR(dentry))
break;
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -75,7 +75,6 @@ extern struct file *nameidata_to_filp(st
extern void release_open_intent(struct nameidata *);

extern struct dentry *lookup_one_len(const char *, struct dentry *, int);
-extern struct dentry *lookup_one_noperm(const char *, struct dentry *);

extern int follow_down(struct vfsmount **, struct dentry **);
extern int follow_up(struct vfsmount **, struct dentry **);



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