[CRIU] [PATCH] mount: Find NS_ROOT for cr-time mount on restore

[Andrei Vagin]

On Fri, May 19, 2017 at 03:13:09PM +0300, Kirill Tkhai wrote:
> After commit 2e8970beda5b "mount: create a mount point
> for the root mount namespace in the roots yard", top
> of the tree of mount_infos points to the fake mount.
> So, when we're looking for appropriate place for
> binfmt_misc, we can't find "xxx/proc/sys/fs/binfmt_misc".
> Fix that by finding real NS_ROOT manually.
> 
> https://jira.sw.ru/browse/PSBM-66457

pls, don't add links which are not available for everyone
> 
> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> ---
>  criu/mount.c |   34 ++++++++++++++++++++++++++++++----
>  1 file changed, 30 insertions(+), 4 deletions(-)
> 
> diff --git a/criu/mount.c b/criu/mount.c
> index 634491310..cef7e7437 100644
> --- a/criu/mount.c
> +++ b/criu/mount.c
> @@ -42,7 +42,7 @@
>  #undef	LOG_PREFIX
>  #define LOG_PREFIX "mnt: "
>  
> -#define BINFMT_MISC_HOME "/proc/sys/fs/binfmt_misc"
> +#define BINFMT_MISC_HOME "proc/sys/fs/binfmt_misc"
>  #define CRTIME_MNT_ID 0
>  
>  /* A helper mount_info entry for the roots yard */
> @@ -1194,15 +1194,41 @@ int open_mountpoint(struct mount_info *pm)
>  static __maybe_unused int add_cr_time_mount(struct mount_info *root, char *fsname, const char *path, unsigned int s_dev)
>  {
>  	struct mount_info *mi, *t, *parent;
> +	bool add_slash = false;
> +	int len;
> +
> +	if (!root->nsid) {
> +		/* On restore we have fake top mount_info. Find real NS_ROOT */
> +		list_for_each_entry(t, &root->children, siblings)
> +			if (t->nsid->type == NS_ROOT) {
> +				root = t;
> +				break;
> +			}
> +		if (!root->nsid) {
> +			pr_err("Can't find NS_ROOT\n");
> +			return -1;
> +		}
> +	}
>  
>  	mi = mnt_entry_alloc();
>  	if (!mi)
>  		return -1;
> -	mi->mountpoint = xmalloc(strlen(path) + 2);
> +
> +	len = strlen(root->mountpoint);
> +	/* It may be "./" or "./path/to/dir" */
> +	if (root->mountpoint[len - 1] != '/') {
> +		add_slash = true;
> +		len++;
> +	}
> +
> +	mi->mountpoint = xmalloc(len + strlen(path) + 1);
>  	if (!mi->mountpoint)
>  		return -1;
>  	mi->ns_mountpoint = mi->mountpoint;
> -	sprintf(mi->mountpoint, ".%s", path);
> +	if (!add_slash)
> +		sprintf(mi->mountpoint, "%s%s", root->mountpoint, path);
> +	else
> +		sprintf(mi->mountpoint, "%s/%s", root->mountpoint, path);
>  	mi->mnt_id = CRTIME_MNT_ID;
>  	mi->flags = mi->sb_flags = 0;
>  	mi->root = xstrdup("/");
> @@ -3243,7 +3269,7 @@ int collect_mnt_namespaces(bool for_dump)
>  		}
>  
>  		if (ns) {
> -			ret = mount_cr_time_mount(ns, &s_dev, "binfmt_misc", BINFMT_MISC_HOME,
> +			ret = mount_cr_time_mount(ns, &s_dev, "binfmt_misc", "/" BINFMT_MISC_HOME,
>  						  "binfmt_misc");
>  			if (ret == -EPERM)
>  				pr_info("Can't mount binfmt_misc: EPERM. Running in user_ns?\n");
>