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Fix to work lxc-start with unprivileged containers on recent kernel

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Change chown_mapped_root() to map in both the root uid and gid, not
just the uid, so as to work lxc-start with unprivileged containers on
recent kernel.

Signed-off-by: TAMUKI Shoichi <tamuki@linet.gr.jp>
Signed-off-by: KATOH Yasufumi <karma@jazz.email.ne.jp>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
This commit is contained in:
TAMUKI Shoichi 2014-06-27 17:29:01 +09:00 committed by Stéphane Graber
parent 3fdd0ca89e
commit 7b50c609e4
1 changed files with 72 additions and 21 deletions
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93
src/lxc/conf.c
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@ -3327,7 +3327,8 @@ int lxc_map_ids(struct lxc_list *idmap, pid_t pid)
}
/*
* return the host uid to which the container root is mapped in *val.
* return the host uid/gid to which the container root is mapped in
* *val.
* Return true if id was found, false otherwise.
*/
bool get_mapped_rootid(struct lxc_conf *conf, enum idtype idtype,
@ -3338,7 +3339,7 @@ bool get_mapped_rootid(struct lxc_conf *conf, enum idtype idtype,
lxc_list_for_each(it, &conf->id_map) {
map = it->elem;
if (map->idtype != ID_TYPE_UID)
if (map->idtype != idtype)
continue;
if (map->nsid != 0)
continue;
@ -3492,15 +3493,17 @@ void lxc_delete_tty(struct lxc_tty_info *tty_info)
}
/*
* chown_mapped_root: for an unprivileged user with uid X to chown a dir
* to subuid Y, he needs to run chown as root in a userns where
* nsid 0 is mapped to hostuid Y, and nsid Y is mapped to hostuid
* X. That way, the container root is privileged with respect to
* hostuid X, allowing him to do the chown.
* chown_mapped_root: for an unprivileged user with uid/gid X to
* chown a dir to subuid/subgid Y, he needs to run chown as root
* in a userns where nsid 0 is mapped to hostuid/hostgid Y, and
* nsid Y is mapped to hostuid/hostgid X. That way, the container
* root is privileged with respect to hostuid/hostgid X, allowing
* him to do the chown.
*/
int chown_mapped_root(char *path, struct lxc_conf *conf)
{
uid_t rootid;
uid_t rootuid;
gid_t rootgid;
pid_t pid;
unsigned long val;
char *chownpath = path;
@ -3509,7 +3512,12 @@ int chown_mapped_root(char *path, struct lxc_conf *conf)
ERROR("No mapping for container root");
return -1;
}
rootid = (uid_t) val;
rootuid = (uid_t) val;
if (!get_mapped_rootid(conf, ID_TYPE_GID, &val)) {
ERROR("No mapping for container root");
return -1;
}
rootgid = (gid_t) val;
/*
* In case of overlay, we want only the writeable layer
@ -3530,14 +3538,14 @@ int chown_mapped_root(char *path, struct lxc_conf *conf)
}
path = chownpath;
if (geteuid() == 0) {
if (chown(path, rootid, -1) < 0) {
if (chown(path, rootuid, rootgid) < 0) {
ERROR("Error chowning %s", path);
return -1;
}
return 0;
}
if (rootid == geteuid()) {
if (rootuid == geteuid()) {
// nothing to do
INFO("%s: container root is our uid; no need to chown" ,__func__);
return 0;
@ -3549,13 +3557,31 @@ int chown_mapped_root(char *path, struct lxc_conf *conf)
return -1;
}
if (!pid) {
int hostuid = geteuid(), ret;
char map1[100], map2[100], map3[100];
char *args[] = {"lxc-usernsexec", "-m", map1, "-m", map2, "-m",
map3, "--", "chown", "0", path, NULL};
int hostuid = geteuid(), hostgid = getegid(), ret;
struct stat sb;
char map1[100], map2[100], map3[100], map4[100], map5[100];
char ugid[100];
char *args1[] = { "lxc-usernsexec", "-m", map1, "-m", map2,
"-m", map3, "-m", map5,
"--", "chown", ugid, path, NULL };
char *args2[] = { "lxc-usernsexec", "-m", map1, "-m", map2,
"-m", map3, "-m", map4, "-m", map5,
"--", "chown", ugid, path, NULL };
// "u:0:rootid:1"
ret = snprintf(map1, 100, "u:0:%d:1", rootid);
// save the current gid of "path"
if (stat(path, &sb) < 0) {
ERROR("Error stat %s", path);
return -1;
}
// a trick for chgrp the file that is not owned by oneself
if (chown(path, -1, hostgid) < 0) {
ERROR("Error chgrp %s", path);
return -1;
}
// "u:0:rootuid:1"
ret = snprintf(map1, 100, "u:0:%d:1", rootuid);
if (ret < 0 || ret >= 100) {
ERROR("Error uid printing map string");
return -1;
@ -3568,14 +3594,39 @@ int chown_mapped_root(char *path, struct lxc_conf *conf)
return -1;
}
// "g:0:hostgid:1"
ret = snprintf(map3, 100, "g:0:%d:1", getgid());
// "g:0:rootgid:1"
ret = snprintf(map3, 100, "g:0:%d:1", rootgid);
if (ret < 0 || ret >= 100) {
ERROR("Error uid printing map string");
ERROR("Error gid printing map string");
return -1;
}
ret = execvp("lxc-usernsexec", args);
// "g:pathgid:rootgid+pathgid:1"
ret = snprintf(map4, 100, "g:%d:%d:1", sb.st_gid,
rootgid + sb.st_gid);
if (ret < 0 || ret >= 100) {
ERROR("Error gid printing map string");
return -1;
}
// "g:hostgid:hostgid:1"
ret = snprintf(map5, 100, "g:%d:%d:1", hostgid, hostgid);
if (ret < 0 || ret >= 100) {
ERROR("Error gid printing map string");
return -1;
}
// "0:pathgid" (chown)
ret = snprintf(ugid, 100, "0:%d", sb.st_gid);
if (ret < 0 || ret >= 100) {
ERROR("Error owner printing format string for chown");
return -1;
}
if (hostgid == sb.st_gid)
ret = execvp("lxc-usernsexec", args1);
else
ret = execvp("lxc-usernsexec", args2);
SYSERROR("Failed executing usernsexec");
exit(1);
}