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authorEric W. Biederman <ebiederm@xmission.com>2012-12-14 08:50:54 -0800
committerEric W. Biederman <ebiederm@xmission.com>2012-12-14 18:36:26 -0800
commitaa6d054e5ce94720797ca260392a74dbced56412 (patch)
tree4e7093d4e288238f0514187e87b13738504a21df /kernel/cred.c
parent5e4a08476b50fa39210fca82e03325cc46b9c235 (diff)
downloadlinux-aa6d054e5ce94720797ca260392a74dbced56412.tar.gz
userns: Add a more complete capability subset test to commit_creds
When unsharing a user namespace we reduce our credentials to just what can be done in that user namespace. This is a subset of the credentials we previously had. Teach commit_creds to recognize this is a subset of the credentials we have had before and don't clear the dumpability flag. This allows an unprivileged program to do: unshare(CLONE_NEWUSER); fd = open("/proc/self/uid_map", O_RDWR); Where previously opening the uid_map writable would fail because the the task had been made non-dumpable. Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'kernel/cred.c')
-rw-r--r--kernel/cred.c27
1 files changed, 26 insertions, 1 deletions
diff --git a/kernel/cred.c b/kernel/cred.c
index 48cea3da6d0..709d521903f 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -455,6 +455,31 @@ error_put:
return ret;
}
+static bool cred_cap_issubset(const struct cred *set, const struct cred *subset)
+{
+ const struct user_namespace *set_ns = set->user_ns;
+ const struct user_namespace *subset_ns = subset->user_ns;
+
+ /* If the two credentials are in the same user namespace see if
+ * the capabilities of subset are a subset of set.
+ */
+ if (set_ns == subset_ns)
+ return cap_issubset(subset->cap_permitted, set->cap_permitted);
+
+ /* The credentials are in a different user namespaces
+ * therefore one is a subset of the other only if a set is an
+ * ancestor of subset and set->euid is owner of subset or one
+ * of subsets ancestors.
+ */
+ for (;subset_ns != &init_user_ns; subset_ns = subset_ns->parent) {
+ if ((set_ns == subset_ns->parent) &&
+ uid_eq(subset_ns->owner, set->euid))
+ return true;
+ }
+
+ return false;
+}
+
/**
* commit_creds - Install new credentials upon the current task
* @new: The credentials to be assigned
@@ -493,7 +518,7 @@ int commit_creds(struct cred *new)
!gid_eq(old->egid, new->egid) ||
!uid_eq(old->fsuid, new->fsuid) ||
!gid_eq(old->fsgid, new->fsgid) ||
- !cap_issubset(new->cap_permitted, old->cap_permitted)) {
+ !cred_cap_issubset(old, new)) {
if (task->mm)
set_dumpable(task->mm, suid_dumpable);
task->pdeath_signal = 0;