[CRIU] [PATCH] pipes: Restore pipe size via userns call

[Andrei Vagin]

On Fri, Feb 03, 2017 at 09:28:23PM +0300, Cyrill Gorcunov wrote:
> From: Cyrill Gorcunov <gorcunov at virtuozzo.com>
> 
> In vanilla kernels starting from v4.4-6172-g759c011
> pipes allocation is limited per user-namespace, and
> what is more interesting is that if hard limit is
> zero but softlimit is not, then it is possible to
> create new pipes with one buffer but setting its
> size if not allowed until we're having CAP_SYS_RESOURCE
> and CAP_SYS_ADMIN caps granted.
> 
> So to be able to restore this resource we need
> to use userns daemon.
> 
> Signed-off-by: Cyrill Gorcunov <gorcunov at virtuozzo.com>
> ---
>  criu/pipes.c | 32 +++++++++++++++++++++++++-------
>  1 file changed, 25 insertions(+), 7 deletions(-)
> 
> diff --git a/criu/pipes.c b/criu/pipes.c
> index 7be1d5f047a1..26aa2b4c359f 100644
> --- a/criu/pipes.c
> +++ b/criu/pipes.c
> @@ -11,6 +11,7 @@
>  #include "pipes.h"
>  #include "util-pie.h"
>  #include "autofs.h"
> +#include "namespaces.h"
>  
>  #include "protobuf.h"
>  #include "util.h"
> @@ -142,6 +143,25 @@ static int mark_pipe_master(void *unused)
>  
>  static struct pipe_data_rst *pd_hash_pipes[PIPE_DATA_HASH_SIZE];
>  
> +typedef struct {
> +	unsigned int	pipe_id;
> +	size_t		size;
> +} pipe_set_size_arg_t;
> +
> +static int pipe_set_size(void *arg, int fd, int pid)
> +{
> +	pipe_set_size_arg_t *p = arg;
> +
> +	pr_info("Restoring size %#zx for %#x\n", p->size, p->pipe_id);
> +
> +	if (fcntl(fd, F_SETPIPE_SZ, p->size) < 0) {
> +		pr_perror("Can't restore pipe size");
> +		return -1;
> +	}
> +
> +	return 0;
> +}
> +
>  int restore_pipe_data(int img_type, int pfd, u32 id, struct pipe_data_rst **hash)
>  {
>  	int ret;
> @@ -201,13 +221,11 @@ int restore_pipe_data(int img_type, int pfd, u32 id, struct pipe_data_rst **hash
>  out:
>  	ret = 0;
>  	if (pd->pde->has_size) {
> -		pr_info("Restoring size %#x for %#x\n",
> -				pd->pde->size, pd->pde->pipe_id);
> -		ret = fcntl(pfd, F_SETPIPE_SZ, pd->pde->size);
> -		if (ret < 0)
> -			pr_perror("Can't restore pipe size");
> -		else
> -			ret = 0;
> +		pipe_set_size_arg_t args = {
> +			.pipe_id	= pd->pde->pipe_id,
> +			.size		= (size_t)pd->pde->size,
> +		};
> +		ret = userns_call(pipe_set_size, UNS_ASYNC, &args, sizeof(args), pfd);

UNS_ASYNC is used to improve perfomance, isn't it? If it is, I would
suggest to try to set a pipe size here and make userns_call only if it is failed
with EPERM. In this case we can do this synchroniously, because the
number of these calls probably will be small. And you will be able to
apply Pavel's comment.

>  	}
>  err:
>  	return ret;
> -- 
> 2.7.4
> 
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