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Subject[PATCH v3 05/25] user_namespace: refactor map_write()
Date
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>
---
/* 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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