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uidmap: fix writing multiple ranges

The kernel requires a single atomic write for setting the /proc
idmap files. We were calling write(2) more than once when multiple
ranges were configured so instead build a buffer to pass in one write(2)
call.

Change id types to unsigned long to handle large id mappings gracefully.

Fix max id in example comment.

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
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commit 251d0d2a8b4ec7a12c22ba63b5d0e558289c2ef6 1 parent a84b993
Dwight Engen authored stgraber committed
Showing with 39 additions and 17 deletions.
  1. +28 −6 src/lxc/conf.c
  2. +8 −8 src/lxc/conf.h
  3. +3 −3 src/lxc/confile.c
View
34 src/lxc/conf.c
@@ -2447,7 +2447,8 @@ int lxc_assign_network(struct lxc_list *network, pid_t pid)
return 0;
}
-static int add_id_mapping(enum idtype idtype, pid_t pid, uid_t ns_start, uid_t host_start, int range)
+static int write_id_mapping(enum idtype idtype, pid_t pid, const char *buf,
+ size_t buf_size)
{
char path[PATH_MAX];
int ret, closeret;
@@ -2463,7 +2464,7 @@ static int add_id_mapping(enum idtype idtype, pid_t pid, uid_t ns_start, uid_t h
perror("open");
return -EINVAL;
}
- ret = fprintf(f, "%d %d %d", ns_start, host_start, range);
+ ret = fwrite(buf, buf_size, 1, f);
if (ret < 0)
SYSERROR("writing id mapping");
closeret = fclose(f);
@@ -2477,13 +2478,34 @@ int lxc_map_ids(struct lxc_list *idmap, pid_t pid)
struct lxc_list *iterator;
struct id_map *map;
int ret = 0;
-
- lxc_list_for_each(iterator, idmap) {
- map = iterator->elem;
- ret = add_id_mapping(map->idtype, pid, map->nsid, map->hostid, map->range);
+ 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;
+
+ for(type = ID_TYPE_UID; type <= ID_TYPE_GID; type++) {
+ int left,fill;
+ lxc_list_for_each(iterator, idmap) {
+ map = iterator->elem;
+ if (map->idtype == type) {
+ left = 4096 - (pos - buf);
+ fill = snprintf(pos, left, "%lu %lu %lu\n",
+ map->nsid, map->hostid, map->range);
+ if (fill <= 0 || fill >= left)
+ SYSERROR("snprintf failed, too many mappings");
+ pos += fill;
+ }
+ }
+ ret = write_id_mapping(type, pid, buf, pos-buf);
if (ret)
break;
+ pos = buf;
}
+
+ free(buf);
return ret;
}
View
16 src/lxc/conf.h
@@ -149,17 +149,17 @@ enum idtype {
/*
* id_map is an id map entry. Form in confile is:
- * lxc.id_map = U 9800 0 100
- * lxc.id_map = U 9900 1000 100
- * lxc.id_map = G 9800 0 100
- * lxc.id_map = G 9900 1000 100
- * meaning the container can use uids and gids 0-100 and 1000-1100,
- * with uid 0 mapping to uid 9800 on the host, and gid 1000 to
- * gid 9900 on the host.
+ * lxc.id_map = u 0 9800 100
+ * lxc.id_map = u 1000 9900 100
+ * lxc.id_map = g 0 9800 100
+ * lxc.id_map = g 1000 9900 100
+ * meaning the container can use uids and gids 0-99 and 1000-1099,
+ * with [ug]id 0 mapping to [ug]id 9800 on the host, and [ug]id 1000 to
+ * [ug]id 9900 on the host.
*/
struct id_map {
enum idtype idtype;
- int hostid, nsid, range;
+ unsigned long hostid, nsid, range;
};
/*
View
6 src/lxc/confile.c
@@ -1114,7 +1114,7 @@ static int config_idmap(const char *key, const char *value, struct lxc_conf *lxc
char *subkey;
struct lxc_list *idmaplist = NULL;
struct id_map *idmap = NULL;
- int hostid, nsid, range;
+ unsigned long hostid, nsid, range;
char type;
int ret;
@@ -1139,10 +1139,10 @@ static int config_idmap(const char *key, const char *value, struct lxc_conf *lxc
lxc_list_add_tail(&lxc_conf->id_map, idmaplist);
- ret = sscanf(value, "%c %d %d %d", &type, &nsid, &hostid, &range);
+ ret = sscanf(value, "%c %lu %lu %lu", &type, &nsid, &hostid, &range);
if (ret != 4)
goto out;
- INFO("read uid map: type %c nsid %d hostid %d range %d", type, nsid, hostid, range);
+ INFO("read uid map: type %c nsid %lu hostid %lu range %lu", type, nsid, hostid, range);
if (type == 'u')
idmap->idtype = ID_TYPE_UID;
else if (type == 'g')
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