[lxc-devel] [PATCH 1/1] lxc_id_mapping: don't try to write mappings if there are none

[Dwight Engen]

Thanks for fixing this up Serge, sorry about the regression!

On Wed, 13 Mar 2013 10:33:00 -0500
Serge Hallyn <serge.hallyn at ubuntu.com> wrote:

> Otherwise containers fail to start even if they aren't trying to map
> ids.
> 
> Also don't allocate buf unless we need to.
> 
> Reported-by: Alexander Vladimirov
> <alexander.idkfa.vladimirov at gmail.com> Signed-off-by: Serge Hallyn
> <serge.hallyn at ubuntu.com> ---
>  src/lxc/conf.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/src/lxc/conf.c b/src/lxc/conf.c
> index 85e1c61..af75690 100644
> --- a/src/lxc/conf.c
> +++ b/src/lxc/conf.c
> @@ -2479,17 +2479,20 @@ int lxc_map_ids(struct lxc_list *idmap, pid_t
> pid) struct lxc_list *iterator;
>  	struct id_map *map;
>  	int ret = 0;
> -	char *buf,*pos;
>  	enum idtype type;
> -
> -	/* The kernel only takes <= 4k for writes
> to /proc/<nr>/[ug]id_map */
> -	buf = pos = malloc(4096);
> -	if (!buf)
> -		return -ENOMEM;
> +	char *buf = NULL, *pos;
>  
>  	for(type = ID_TYPE_UID; type <= ID_TYPE_GID; type++) {
> -		int left,fill;
> +		int left, fill;
> +
> +		pos = buf;
>  		lxc_list_for_each(iterator, idmap) {
> +			/* The kernel only takes <= 4k for writes
> to /proc/<nr>/[ug]id_map */
> +			if (!buf)
> +				buf = pos = malloc(4096);
> +			if (!buf)
> +				return -ENOMEM;
> +
>  			map = iterator->elem;
>  			if (map->idtype == type) {
>  				left = 4096 - (pos - buf);
> @@ -2500,13 +2503,15 @@ int lxc_map_ids(struct lxc_list *idmap, pid_t
> pid) pos += fill;
>  			}
>  		}
> +		if (pos == buf) // no mappings were found
> +			continue;
>  		ret = write_id_mapping(type, pid, buf, pos-buf);
>  		if (ret)
>  			break;
> -		pos = buf;
>  	}
>  
> -	free(buf);
> +	if (buf)
> +		free(buf);
>  	return ret;
>  }
>