git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git
for-testing
commit a8c473e95079 ("fs: Limit file caps to the user namespace of the super
block")
Capability sets attached to files must be ignored except in the
user namespaces where the mounter is privileged, i.e. s_user_ns
and its descendants. Otherwise a vector exists for gaining
privileges in namespaces where a user is not already privileged.
Add a new helper function, in_user_ns(), to test whether a user
namespace is the same as or a descendant of another namespace.
Use this helper to determine whether a file's capability set
should be applied to the caps constructed during exec.
Acked-by: Serge Hallyn <[email protected]>
Signed-off-by: Seth Forshee <[email protected]>
Signed-off-by: Eric W. Biederman <[email protected]>
Signed-off-by: Pavel Tikhomirov <[email protected]>
---
include/linux/user_namespace.h | 8 ++++++++
kernel/user_namespace.c | 14 ++++++++++++++
security/commoncap.c | 2 ++
3 files changed, 24 insertions(+)
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 9b17627..4e4f56e 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -74,6 +74,8 @@ extern ssize_t proc_projid_map_write(struct file *, const
char __user *, size_t,
extern ssize_t proc_setgroups_write(struct file *, const char __user *,
size_t, loff_t *);
extern int proc_setgroups_show(struct seq_file *m, void *v);
extern bool userns_may_setgroups(const struct user_namespace *ns);
+extern bool in_userns(const struct user_namespace *ns,
+ const struct user_namespace *target_ns);
#else
static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
@@ -102,6 +104,12 @@ static inline bool userns_may_setgroups(const struct
user_namespace *ns)
{
return true;
}
+
+static inline bool in_userns(const struct user_namespace *ns,
+ const struct user_namespace *target_ns)
+{
+ return true;
+}
#endif
void update_mnt_policy(struct user_namespace *userns);
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index fe53b77..6733b5f 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -949,6 +949,20 @@ bool userns_may_setgroups(const struct user_namespace *ns)
return allowed;
}
+/*
+ * Returns true if @ns is the same namespace as or a descendant of
+ * @target_ns.
+ */
+bool in_userns(const struct user_namespace *ns,
+ const struct user_namespace *target_ns)
+{
+ for (; ns; ns = ns->parent) {
+ if (ns == target_ns)
+ return true;
+ }
+ return false;
+}
+
static void *userns_get(struct task_struct *task)
{
struct user_namespace *user_ns;
diff --git a/security/commoncap.c b/security/commoncap.c
index af80f74..c313a40 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -445,6 +445,8 @@ static int get_file_caps(struct linux_binprm *bprm, bool
*effective, bool *has_c
if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)
return 0;
+ if (!in_userns(current_user_ns(),
bprm->file->f_path.mnt->mnt_sb->s_user_ns))
+ return 0;
dentry = dget(bprm->file->f_dentry);
--
1.9.3
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