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SubjectRe: [PATCH] force dentry revalidation after namespace change
Quoting Glauber Costa (glommer@parallels.com):
> 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 <glommer@parallels.com>

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

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

> CC: Tejun Heo <tj@kernel.org>
> CC: Eric W. Biederman <ebiederm@xmission.com>
> CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
> 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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