[PATCH review 04/16] userns: Allow setting a userns mapping to your current uid.

[Eric W. Biederman]

From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>

Acked-by: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
---
 kernel/user_namespace.c |   15 +++++++++++++++
 1 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 456a6b9..49096d5 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -709,6 +709,21 @@ ssize_t proc_projid_map_write(struct file *file, const char __user *buf, size_t
 static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
 				struct uid_gid_map *new_map)
 {
+	/* Allow mapping to your own filesystem ids */
+	if ((new_map->nr_extents == 1) && (new_map->extent[0].count == 1)) {
+		u32 id = new_map->extent[0].lower_first;
+		if (cap_setid == CAP_SETUID) {
+			kuid_t uid = make_kuid(ns->parent, id);
+			if (uid_eq(uid, current_fsuid()))
+				return true;
+		}
+		else if (cap_setid == CAP_SETGID) {
+			kgid_t gid = make_kgid(ns->parent, id);
+			if (gid_eq(gid, current_fsgid()))
+				return true;
+		}
+	}
+
 	/* Allow anyone to set a mapping that doesn't require privilege */
 	if (!cap_valid(cap_setid))
 		return true;
-- 
1.7.5.4

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