Subject: Re: [PATCH] force dentry revalidation after namespace change

From: "Serge E. Hallyn" <[email-masked]>
Date: Thu, 5 Jul 2012 22:17:01 +0000

Quoting Glauber Costa ([email-masked]):
> 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

Confirmed that it currently fails to fail :)

> 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.
> 
> Signed-off-by: Glauber Costa <[email-masked]>

Haven't run it, but the patch looks good.  Thanks, Glauber.

Acked-by: Serge Hallyn <[email-masked]>

> CC: Tejun Heo <[email-masked]>
> CC: Eric W. Biederman <[email-masked]>
> CC: Greg Kroah-Hartman <[email-masked]>
> ---
>  fs/sysfs/dir.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
> index e6bb9b2..c24bdd9 100644
> --- 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;
> @@ -314,6 +315,10 @@ static int sysfs_dentry_revalidate(struct dentry *dentry, struct nameidata *nd)
>  	sd = dentry->d_fsdata;
>  	mutex_lock(&sysfs_mutex);
>  
> +	type = sysfs_ns_type(sd);
> +	if (sd->s_ns && (sysfs_info(dentry->d_sb)->ns[type] != sd->s_ns))
> +		goto out_bad;
> +
>  	/* The sysfs dirent has been deleted */
>  	if (sd->s_flags & SYSFS_FLAG_REMOVED)
>  		goto out_bad;
> -- 
> 1.7.10.4
> 
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