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SubjectRe: [PATCH v2] fail dentry revalidation after namespace change
Quoting Andrew Morton (akpm@linux-foundation.org):
> On Fri, 6 Jul 2012 13:09:07 +0400
> Glauber Costa <glommer@parallels.com> wrote:
>
> > When we change the namespace tag of a sysfs entry, the associated dentry
> > is still kept around. readdir() will work correctly and not display the
> > old entries, but open() will still succeed, so will reads and writes.
> >
> > This will no longer happen if sysfs is remounted, hinting that this is a
> > cache-related problem.
> >
> > I am using the following sequence to demonstrate that:
> >
> > shell1:
> > ip link add type veth
> > unshare -nm
> >
> > shell2:
> > ip link set veth1 <pid_of_shell_1>
> > cat /sys/devices/virtual/net/veth1/ifindex
> >
> > Before that patch, this will succeed (fail to fail). After it, it will
> > correctly return an error. Differently from a normal rename, which we
> > handle fine, changing the object namespace will keep it's path intact.
> > So this check seems necessary as well.
> >
> > ...
> >
> > --- a/fs/sysfs/dir.c
> > +++ b/fs/sysfs/dir.c
> > @@ -307,6 +307,7 @@ static int sysfs_dentry_revalidate(struct dentry *dentry, struct nameidata *nd)
> > {
> > struct sysfs_dirent *sd;
> > int is_dir;
> > + int type;
> >
> > if (nd->flags & LOOKUP_RCU)
> > return -ECHILD;
> > @@ -326,6 +327,13 @@ static int sysfs_dentry_revalidate(struct dentry *dentry, struct nameidata *nd)
> > if (strcmp(dentry->d_name.name, sd->s_name) != 0)
> > goto out_bad;
> >
> > + /* The sysfs dirent has been moved to a different namespace */
> > + type = KOBJ_NS_TYPE_NONE;
> > + if (sd->s_parent)
> > + type = sysfs_ns_type(sd->s_parent);
> > + if (type && (sysfs_info(dentry->d_sb)->ns[type] != sd->s_ns))
>
> eww, the code is assuming that KOBJ_NS_TYPE_NONE has a value of zero.
> Don't do that; it smells bad.
>
> I renamed my version of this patch to "sysfs: fail dentry revalidation
> after namespace change", as carefully explained in section 15 of the
> excellent Documentation/SubmittingPatches, then queued this:
>
>
> From: Andrew Morton <akpm@linux-foundation.org>
> Subject: sysfs-fail-dentry-revalidation-after-namespace-change-fix
>
> don't assume that KOBJ_NS_TYPE_NONE==0. Also save a test-n-branch.
>
> Cc: Eric W. Biederman <ebiederm@xmission.com>
> Cc: Glauber Costa <glommer@parallels.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Tejun Heo <tj@kernel.org>

Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>

> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
> fs/sysfs/dir.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff -puN fs/sysfs/dir.c~sysfs-fail-dentry-revalidation-after-namespace-change-fix fs/sysfs/dir.c
> --- a/fs/sysfs/dir.c~sysfs-fail-dentry-revalidation-after-namespace-change-fix
> +++ a/fs/sysfs/dir.c
> @@ -329,10 +329,12 @@ static int sysfs_dentry_revalidate(struc
>
> /* The sysfs dirent has been moved to a different namespace */
> type = KOBJ_NS_TYPE_NONE;
> - if (sd->s_parent)
> + if (sd->s_parent) {
> type = sysfs_ns_type(sd->s_parent);
> - if (type && (sysfs_info(dentry->d_sb)->ns[type] != sd->s_ns))
> - goto out_bad;
> + if (type != KOBJ_NS_TYPE_NONE &&
> + sysfs_info(dentry->d_sb)->ns[type] != sd->s_ns)
> + goto out_bad;
> + }
>
> mutex_unlock(&sysfs_mutex);
> out_valid:
> _
>
>


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