On Tue, 16 Apr 2013 15:17:44 +0400
Stanislav Kinsbursky <skinsbur...@parallels.com> wrote:
> This patch adds support for UserModeHelper tracker in a container.
> The reason for this is that the only containerised tracker ("nfsdcld") is
> going to be removed in 3.10 kernel, thus at least one more tracker have to be
> containerised to replace the deprecated one.
> UMH tracker looks more preferable comparing to legacy since it's the latest
> one.
> To make UMH tracker work in a container, we have to make sure, that it
> executes right binary (i.e., this binary have to be taken from the container
> environment).
> But, UMH is a kernel thread, which works in global root environment by design
> (kernel thread's root is inherited from kthreadd, which in turn inherited it's
> root from global init). So, the root have to be swapped to the container's
> one before binary execution.
>
> This patch passes "init" callback and private "data" to UMH interface, which
> are used to swap root for spawned kernel thread.
>
> Note: container's root can be stored on stack, because UMH calls are
> synchronous.
>
> Signed-off-by: Stanislav Kinsbursky <skinsbur...@parallels.com>
> ---
> fs/nfsd/nfs4recover.c | 29 ++++++++++++++++++++++-------
> 1 files changed, 22 insertions(+), 7 deletions(-)
>
> diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
> index 899ca26..15f8de6 100644
> --- a/fs/nfsd/nfs4recover.c
> +++ b/fs/nfsd/nfs4recover.c
> @@ -38,6 +38,7 @@
> #include <linux/crypto.h>
> #include <linux/sched.h>
> #include <linux/fs.h>
> +#include <linux/fs_struct.h>
> #include <linux/module.h>
> #include <net/net_namespace.h>
> #include <linux/sunrpc/rpc_pipe_fs.h>
> @@ -1122,12 +1123,28 @@ nfsd4_cltrack_legacy_recdir(const struct xdr_netobj
> *name)
> return result;
> }
>
> +static int nfsd_swap_root(struct subprocess_info *info, struct cred *new)
> +{
> + struct path *root = info->data;
> + struct fs_struct *fs = current->fs;
> + struct path current_root;
> +
> + spin_lock(&fs->lock);
> + current_root = fs->root;
> + fs->root = *root;
> + spin_unlock(&fs->lock);
> + if (current_root.dentry)
> + path_put(¤t_root);
> + return 0;
> +}
> +
> static int
> nfsd4_umh_cltrack_upcall(char *cmd, char *arg, char *legacy)
> {
> char *envp[2];
> char *argv[4];
> int ret;
> + struct path root;
>
> if (unlikely(!cltrack_prog[0])) {
> dprintk("%s: cltrack_prog is disabled\n", __func__);
> @@ -1146,7 +1163,11 @@ nfsd4_umh_cltrack_upcall(char *cmd, char *arg, char
> *legacy)
> argv[2] = arg;
> argv[3] = NULL;
>
> - ret = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_PROC);
> + get_fs_root(current->fs, &root);
> +
> + ret = call_usermodehelper_fns(argv[0], argv, envp, UMH_WAIT_PROC,
> + nfsd_swap_root, NULL, &root);
> +
> /*
> * Disable the upcall mechanism if we're getting an ENOENT or EACCES
> * error. The admin can re-enable it on the fly by using sysfs
> @@ -1185,12 +1206,6 @@ bin_to_hex_dup(const unsigned char *src, int srclen)
> static int
> nfsd4_umh_cltrack_init(struct net __attribute__((unused)) *net)
> {
> - /* XXX: The usermode helper s not working in container yet. */
> - if (net != &init_net) {
> - WARN(1, KERN_ERR "NFSD: attempt to initialize umh client "
> - "tracking in a container!\n");
> - return -EINVAL;
> - }
> return nfsd4_umh_cltrack_upcall("init", NULL, NULL);
> }
>
>
I think this looks correct and like it'll work, but I wonder whether
we'd be best served by making this part of the UMH code itself?
IOW, add some fields to the struct subprocess_info to hold the new
root, and then do what you're doing in nfsd_swap_root before calling
the "init" function?
I imagine we'll eventually need do something similar for at least some
of the callers of call_usermodehelper so it would make sense to me to
not replicate copies of nfsd_swap_root all over the place.
--
Jeff Layton <jlay...@redhat.com>
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