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SubjectRe: [PATCH v3 05/25] user_namespace: refactor map_write()
On Tue, Feb 18, 2020 at 03:33:51PM +0100, Christian Brauner wrote:
> Refactor map_write() to prepare for adding fsid mappings support. This mainly
> factors out various open-coded parts into helpers that can be reused in the
> follow up patch.
>
> Cc: Jann Horn <jannh@google.com>
> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Acked-by: Serge Hallyn <serge@hallyn.com>

> ---
> /* v2 */
> patch not present
>
> /* v3 */
> patch added
> - Jann Horn <jannh@google.com>:
> - Split changes to map_write() to implement fsid mappings into three separate
> patches: basic fsid helpers, preparatory changes to map_write(), actual
> fsid mapping support in map_write().
> ---
> kernel/user_namespace.c | 117 +++++++++++++++++++++++++---------------
> 1 file changed, 74 insertions(+), 43 deletions(-)
>
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 2cfd1e519cc4..e91141262bcc 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -1038,10 +1038,10 @@ static int cmp_extents_reverse(const void *a, const void *b)
> }
>
> /**
> - * sort_idmaps - Sorts an array of idmap entries.
> + * sort_map - Sorts an array of idmap entries.
> * Can only be called if number of mappings exceeds UID_GID_MAP_MAX_BASE_EXTENTS.
> */
> -static int sort_idmaps(struct uid_gid_map *map)
> +static int sort_map(struct uid_gid_map *map)
> {
> if (map->nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
> return 0;
> @@ -1064,6 +1064,71 @@ static int sort_idmaps(struct uid_gid_map *map)
> return 0;
> }
>
> +static int sort_idmaps(struct uid_gid_map *map)
> +{
> + return sort_map(map);
> +}
> +
> +static int map_from_parent(struct uid_gid_map *new_map,
> + struct uid_gid_map *parent_map)
> +{
> + unsigned idx;
> +
> + /* Map the lower ids from the parent user namespace to the
> + * kernel global id space.
> + */
> + for (idx = 0; idx < new_map->nr_extents; idx++) {
> + struct uid_gid_extent *e;
> + u32 lower_first;
> +
> + if (new_map->nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
> + e = &new_map->extent[idx];
> + else
> + e = &new_map->forward[idx];
> +
> + lower_first = map_id_range_down(parent_map, e->lower_first, e->count);
> +
> + /* Fail if we can not map the specified extent to
> + * the kernel global id space.
> + */
> + if (lower_first == (u32)-1)
> + return -EPERM;
> +
> + e->lower_first = lower_first;
> + }
> +
> + return 0;
> +}
> +
> +static int map_into_kids(struct uid_gid_map *id_map,
> + struct uid_gid_map *parent_id_map)
> +{
> + return map_from_parent(id_map, parent_id_map);
> +}
> +
> +static void install_idmaps(struct uid_gid_map *id_map,
> + struct uid_gid_map *new_id_map)
> +{
> + if (new_id_map->nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS) {
> + memcpy(id_map->extent, new_id_map->extent,
> + new_id_map->nr_extents * sizeof(new_id_map->extent[0]));
> + } else {
> + id_map->forward = new_id_map->forward;
> + id_map->reverse = new_id_map->reverse;
> + }
> +}
> +
> +static void free_idmaps(struct uid_gid_map *new_id_map)
> +{
> + if (new_id_map->nr_extents > UID_GID_MAP_MAX_BASE_EXTENTS) {
> + kfree(new_id_map->forward);
> + kfree(new_id_map->reverse);
> + new_id_map->forward = NULL;
> + new_id_map->reverse = NULL;
> + new_id_map->nr_extents = 0;
> + }
> +}
> +
> static ssize_t map_write(struct file *file, const char __user *buf,
> size_t count, loff_t *ppos,
> int cap_setid,
> @@ -1073,7 +1138,6 @@ static ssize_t map_write(struct file *file, const char __user *buf,
> struct seq_file *seq = file->private_data;
> struct user_namespace *ns = seq->private;
> struct uid_gid_map new_map;
> - unsigned idx;
> struct uid_gid_extent extent;
> char *kbuf = NULL, *pos, *next_line;
> ssize_t ret;
> @@ -1191,61 +1255,28 @@ static ssize_t map_write(struct file *file, const char __user *buf,
> if (!new_idmap_permitted(file, ns, cap_setid, &new_map))
> goto out;
>
> - ret = -EPERM;
> - /* Map the lower ids from the parent user namespace to the
> - * kernel global id space.
> - */
> - for (idx = 0; idx < new_map.nr_extents; idx++) {
> - struct uid_gid_extent *e;
> - u32 lower_first;
> -
> - if (new_map.nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
> - e = &new_map.extent[idx];
> - else
> - e = &new_map.forward[idx];
> -
> - lower_first = map_id_range_down(parent_map,
> - e->lower_first,
> - e->count);
> -
> - /* Fail if we can not map the specified extent to
> - * the kernel global id space.
> - */
> - if (lower_first == (u32) -1)
> - goto out;
> -
> - e->lower_first = lower_first;
> - }
> + ret = map_into_kids(&new_map, parent_map);
> + if (ret)
> + goto out;
>
> /*
> * If we want to use binary search for lookup, this clones the extent
> * array and sorts both copies.
> */
> ret = sort_idmaps(&new_map);
> - if (ret < 0)
> + if (ret)
> goto out;
>
> /* Install the map */
> - if (new_map.nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS) {
> - memcpy(map->extent, new_map.extent,
> - new_map.nr_extents * sizeof(new_map.extent[0]));
> - } else {
> - map->forward = new_map.forward;
> - map->reverse = new_map.reverse;
> - }
> + install_idmaps(map, &new_map);
> smp_wmb();
> map->nr_extents = new_map.nr_extents;
>
> *ppos = count;
> ret = count;
> out:
> - if (ret < 0 && new_map.nr_extents > UID_GID_MAP_MAX_BASE_EXTENTS) {
> - kfree(new_map.forward);
> - kfree(new_map.reverse);
> - map->forward = NULL;
> - map->reverse = NULL;
> - map->nr_extents = 0;
> - }
> + if (ret < 0)
> + free_idmaps(&new_map);
>
> mutex_unlock(&userns_state_mutex);
> kfree(kbuf);
> --
> 2.25.0

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