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SubjectRe: [PATCH v2] fail dentry revalidation after namespace change
Glauber Costa <glommer@parallels.com> writes:

> 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.

Note reads and writes of file handles open before the move should
continue to work.

> 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.
>
> [ v2: get type from parent, as suggested by Eric Biederman ]

Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>

> Signed-off-by: Glauber Costa <glommer@parallels.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 | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
> index e6bb9b2..c0bf38a 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;
> @@ -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))
> + goto out_bad;
> +
> mutex_unlock(&sysfs_mutex);
> out_valid:
> return 1;


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