app-emulation/lxc: handle kernels with CAP_SETFCAP

Closes: https://bugs.gentoo.org/789012
Signed-off-by: Joonas Niilola <juippis@gentoo.org>

2 files changed, 94 insertions, 0 deletions

diff --git a/app-emulation/lxc/files/lxc-4.0.9-handle-kernels-with-CAP_SETFCAP.patch b/app-emulation/lxc/files/lxc-4.0.9-handle-kernels-with-CAP_SETFCAP.patch
new file mode 100644
index 000000000000..6fba3c4154a4
--- /dev/null
+++ b/app-emulation/lxc/files/lxc-4.0.9-handle-kernels-with-CAP_SETFCAP.patch
@@ -0,0 +1,93 @@
+From 91ad9b94bcd964adfbaa8d84d8f39304d39835d0 Mon Sep 17 00:00:00 2001
+From: Christian Brauner <christian.brauner@ubuntu.com>
+Date: Thu, 6 May 2021 18:16:45 +0200
+Subject: [PATCH] conf: handle kernels with CAP_SETFCAP
+
+LXC is being very clever and sometimes maps the caller's uid into the
+child userns. This means that the caller can technically write fscaps
+that are valid in the ancestor userns (which can be a security issue in
+some scenarios) so newer kernels require CAP_SETFCAP to do this. Until
+newuidmap/newgidmap are updated to account for this simply write the
+mapping directly in this case.
+
+Cc: stable-4.0
+Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
+---
+ src/lxc/conf.c | 25 ++++++++++++++++++++-----
+ 1 file changed, 20 insertions(+), 5 deletions(-)
+
+diff --git a/src/lxc/conf.c b/src/lxc/conf.c
+index 72e21b5300..f388946970 100644
+--- a/src/lxc/conf.c
++++ b/src/lxc/conf.c
+@@ -2978,6 +2978,9 @@ static int lxc_map_ids_exec_wrapper(void *args)
+ 	return -1;
+ }
+ 
++static struct id_map *find_mapped_hostid_entry(const struct lxc_list *idmap,
++					       unsigned id, enum idtype idtype);
++
+ int lxc_map_ids(struct lxc_list *idmap, pid_t pid)
+ {
+ 	int fill, left;
+@@ -2991,12 +2994,22 @@ int lxc_map_ids(struct lxc_list *idmap, pid_t pid)
+ 	char mapbuf[STRLITERALLEN("new@idmap") + STRLITERALLEN(" ") +
+ 		    INTTYPE_TO_STRLEN(pid_t) + STRLITERALLEN(" ") +
+ 		    LXC_IDMAPLEN] = {0};
+-	bool had_entry = false, use_shadow = false;
++	bool had_entry = false, maps_host_root = false, use_shadow = false;
+ 	int hostuid, hostgid;
+ 
+ 	hostuid = geteuid();
+ 	hostgid = getegid();
+ 
++	/*
++	 * Check whether caller wants to map host root.
++	 * Due to a security fix newer kernels require CAP_SETFCAP when mapping
++	 * host root into the child userns as you would be able to write fscaps
++	 * that would be valid in the ancestor userns. Mapping host root should
++	 * rarely be the case but LXC is being clever in a bunch of cases.
++	 */
++	if (find_mapped_hostid_entry(idmap, 0, ID_TYPE_UID))
++		maps_host_root = true;
++
+ 	/* If new{g,u}idmap exists, that is, if shadow is handing out subuid
+ 	 * ranges, then insist that root also reserve ranges in subuid. This
+ 	 * will protected it by preventing another user from being handed the
+@@ -3014,7 +3027,9 @@ int lxc_map_ids(struct lxc_list *idmap, pid_t pid)
+ 	else if (!gidmap)
+ 		WARN("newgidmap is lacking necessary privileges");
+ 
+-	if (uidmap > 0 && gidmap > 0) {
++	if (maps_host_root) {
++		INFO("Caller maps host root. Writing mapping directly");
++	} else if (uidmap > 0 && gidmap > 0) {
+ 		DEBUG("Functional newuidmap and newgidmap binary found");
+ 		use_shadow = true;
+ 	} else {
+@@ -4229,14 +4244,14 @@ static struct id_map *mapped_nsid_add(const struct lxc_conf *conf, unsigned id,
+ 	return retmap;
+ }
+ 
+-static struct id_map *find_mapped_hostid_entry(const struct lxc_conf *conf,
++static struct id_map *find_mapped_hostid_entry(const struct lxc_list *idmap,
+ 					       unsigned id, enum idtype idtype)
+ {
+ 	struct id_map *map;
+ 	struct lxc_list *it;
+ 	struct id_map *retmap = NULL;
+ 
+-	lxc_list_for_each (it, &conf->id_map) {
++	lxc_list_for_each (it, idmap) {
+ 		map = it->elem;
+ 		if (map->idtype != idtype)
+ 			continue;
+@@ -4265,7 +4280,7 @@ static struct id_map *mapped_hostid_add(const struct lxc_conf *conf, uid_t id,
+ 		return NULL;
+ 
+ 	/* Reuse existing mapping. */
+-	tmp = find_mapped_hostid_entry(conf, id, type);
++	tmp = find_mapped_hostid_entry(&conf->id_map, id, type);
+ 	if (tmp) {
+ 		memcpy(entry, tmp, sizeof(*entry));
+ 	} else {
diff --git a/app-emulation/lxc/lxc-4.0.9.ebuild b/app-emulation/lxc/lxc-4.0.9-r1.ebuild
index 89a0b2e2b2df..8fbfeda5aca7 100644
--- a/app-emulation/lxc/lxc-4.0.9.ebuild
+++ b/app-emulation/lxc/lxc-4.0.9-r1.ebuild
@@ -72,6 +72,7 @@ pkg_setup() {
 }
 
 PATCHES=(
+	"${FILESDIR}"/lxc-4.0.9-handle-kernels-with-CAP_SETFCAP.patch # bug 789012
 	"${FILESDIR}"/${PN}-3.0.0-bash-completion.patch
 	"${FILESDIR}"/${PN}-2.0.5-omit-sysconfig.patch # bug 558854
 )