apparmor: fix unprivileged local user can do privileged policy management

commit 6601e13e82841879406bf9f369032656f441a425 upstream.

Backport for api changes introduced in
- 90c436a64a6e ("apparmor: pass cred through to audit info.")
- 92de220a7f33 ("apparmor: update policy capable checks to use a label")

An unprivileged local user can load, replace, and remove profiles by
opening the apparmorfs interfaces, via a confused deputy attack, by
passing the opened fd to a privileged process, and getting the
privileged process to write to the interface.

This does require a privileged target that can be manipulated to do
the write for the unprivileged process, but once such access is
achieved full policy management is possible and all the possible
implications that implies: removing confinement, DoS of system or
target applications by denying all execution, by-passing the
unprivileged user namespace restriction, to exploiting kernel bugs for
a local privilege escalation.

The policy management interface can not have its permissions simply
changed from 0666 to 0600 because non-root processes need to be able
to load policy to different policy namespaces.

Instead ensure the task writing the interface has privileges that
are a subset of the task that opened the interface. This is already
done via policy for confined processes, but unconfined can delegate
access to the opened fd, by-passing the usual policy check.

Fixes: b7fd2c0340eac ("apparmor: add per policy ns .load, .replace, .remove interface files")
Reported-by: Qualys Security Advisory <qsa@qualys.com>
Tested-by: Salvatore Bonaccorso <carnil@debian.org>
Reviewed-by: Georgia Garcia <georgia.garcia@canonical.com>
Reviewed-by: Cengiz Can <cengiz.can@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/security/apparmor/apparmorfs.c b/security/apparmor/apparmorfs.c
index bd822f13e325305945b396fc8458e5684ad711bc..c73f15c76df9e1663c40dcc3b1451a7b750acee3 100644 (file)
--- a/security/apparmor/apparmorfs.c
+++ b/security/apparmor/apparmorfs.c
@@ -409,7 +409,8 @@ static struct aa_loaddata *aa_simple_write_to_buffer(const char __user *userbuf,
 }
 
 static ssize_t policy_update(u32 mask, const char __user *buf, size_t size,
-                            loff_t *pos, struct aa_ns *ns)
+                            loff_t *pos, struct aa_ns *ns,
+                            const struct cred *ocred)
 {
        struct aa_loaddata *data;
        struct aa_label *label;
@@ -420,7 +421,7 @@ static ssize_t policy_update(u32 mask, const char __user *buf, size_t size,
        /* high level check about policy management - fine grained in
         * below after unpack
         */
-       error = aa_may_manage_policy(label, ns, mask);
+       error = aa_may_manage_policy(current_cred(), label, ns, ocred, mask);
        if (error)
                goto end_section;
 
@@ -441,7 +442,8 @@ static ssize_t profile_load(struct file *f, const char __user *buf, size_t size,
                            loff_t *pos)
 {
        struct aa_ns *ns = aa_get_ns(f->f_inode->i_private);
-       int error = policy_update(AA_MAY_LOAD_POLICY, buf, size, pos, ns);
+       int error = policy_update(AA_MAY_LOAD_POLICY, buf, size, pos, ns,
+                                 f->f_cred);
 
        aa_put_ns(ns);
 
@@ -459,7 +461,7 @@ static ssize_t profile_replace(struct file *f, const char __user *buf,
 {
        struct aa_ns *ns = aa_get_ns(f->f_inode->i_private);
        int error = policy_update(AA_MAY_LOAD_POLICY | AA_MAY_REPLACE_POLICY,
-                                 buf, size, pos, ns);
+                                 buf, size, pos, ns, f->f_cred);
        aa_put_ns(ns);
 
        return error;
@@ -483,7 +485,8 @@ static ssize_t profile_remove(struct file *f, const char __user *buf,
        /* high level check about policy management - fine grained in
         * below after unpack
         */
-       error = aa_may_manage_policy(label, ns, AA_MAY_REMOVE_POLICY);
+       error = aa_may_manage_policy(current_cred(), label, ns,
+                                    f->f_cred, AA_MAY_REMOVE_POLICY);
        if (error)
                goto out;
 
@@ -1797,7 +1800,8 @@ static int ns_mkdir_op(struct user_namespace *mnt_userns, struct inode *dir,
        int error;
 
        label = begin_current_label_crit_section();
-       error = aa_may_manage_policy(label, NULL, AA_MAY_LOAD_POLICY);
+       error = aa_may_manage_policy(current_cred(), label, NULL, NULL,
+                                    AA_MAY_LOAD_POLICY);
        end_current_label_crit_section(label);
        if (error)
                return error;
@@ -1846,7 +1850,8 @@ static int ns_rmdir_op(struct inode *dir, struct dentry *dentry)
        int error;
 
        label = begin_current_label_crit_section();
-       error = aa_may_manage_policy(label, NULL, AA_MAY_LOAD_POLICY);
+       error = aa_may_manage_policy(current_cred(), label, NULL, NULL,
+                                    AA_MAY_LOAD_POLICY);
        end_current_label_crit_section(label);
        if (error)
                return error;

diff --git a/security/apparmor/include/policy.h b/security/apparmor/include/policy.h
index b5aa4231af682a5412b4641c72ef21d49f769f6c..049405dad5a99dffdb07e029e516bea7e4a7b1e8 100644 (file)
--- a/security/apparmor/include/policy.h
+++ b/security/apparmor/include/policy.h
@@ -303,7 +303,8 @@ static inline int AUDIT_MODE(struct aa_profile *profile)
 
 bool policy_view_capable(struct aa_ns *ns);
 bool policy_admin_capable(struct aa_ns *ns);
-int aa_may_manage_policy(struct aa_label *label, struct aa_ns *ns,
-                        u32 mask);
+int aa_may_manage_policy(const struct cred *subj_cred,
+                        struct aa_label *label, struct aa_ns *ns,
+                        const struct cred *ocred, u32 mask);
 
 #endif /* __AA_POLICY_H */

diff --git a/security/apparmor/policy.c b/security/apparmor/policy.c
index 40a2fc50eea19d7abee73c6717c8ece2bbb8529d..760ec0d50f6e8ee70ef2c0613f6dcee2b780bb3e 100644 (file)
--- a/security/apparmor/policy.c
+++ b/security/apparmor/policy.c
@@ -695,14 +695,44 @@ bool policy_admin_capable(struct aa_ns *ns)
        return policy_view_capable(ns) && capable && !aa_g_lock_policy;
 }
 
+static bool is_subset_of_obj_privilege(const struct cred *cred,
+                                      struct aa_label *label,
+                                      const struct cred *ocred)
+{
+       if (cred == ocred)
+               return true;
+
+       if (!aa_label_is_subset(label, cred_label(ocred)))
+               return false;
+       /* don't allow crossing userns for now */
+       if (cred->user_ns != ocred->user_ns)
+               return false;
+       if (!cap_issubset(cred->cap_inheritable, ocred->cap_inheritable))
+               return false;
+       if (!cap_issubset(cred->cap_permitted, ocred->cap_permitted))
+               return false;
+       if (!cap_issubset(cred->cap_effective, ocred->cap_effective))
+               return false;
+       if (!cap_issubset(cred->cap_bset, ocred->cap_bset))
+               return false;
+       if (!cap_issubset(cred->cap_ambient, ocred->cap_ambient))
+               return false;
+       return true;
+}
+
+
 /**
  * aa_may_manage_policy - can the current task manage policy
+ * @subj_cred; subjects cred
  * @label: label to check if it can manage policy
- * @op: the policy manipulation operation being done
+ * @ns: namespace being managed by @label (may be NULL if @label's ns)
+ * @ocred: object cred if request is coming from an open object
+ * @mask: contains the policy manipulation operation being done
  *
  * Returns: 0 if the task is allowed to manipulate policy else error
  */
-int aa_may_manage_policy(struct aa_label *label, struct aa_ns *ns, u32 mask)
+int aa_may_manage_policy(const struct cred *subj_cred, struct aa_label *label,
+                        struct aa_ns *ns, const struct cred *ocred, u32 mask)
 {
        const char *op;
 
@@ -718,6 +748,11 @@ int aa_may_manage_policy(struct aa_label *label, struct aa_ns *ns, u32 mask)
                return audit_policy(label, op, NULL, NULL, "policy_locked",
                                    -EACCES);
 
+       if (ocred && !is_subset_of_obj_privilege(subj_cred, label, ocred))
+               return audit_policy(label, op, NULL, NULL,
+                                   "not privileged for target profile",
+                                   -EACCES);
+
        if (!policy_admin_capable(ns))
                return audit_policy(label, op, NULL, NULL, "not policy admin",
                                    -EACCES);