device_cgroup: Roll back to original exceptions after copy failure

commit e68bfbd3b3c3a0ec3cf8c230996ad8cabe90322f upstream.

When add the 'a *:* rwm' entry to devcgroup A's whitelist, at first A's
exceptions will be cleaned and A's behavior is changed to
DEVCG_DEFAULT_ALLOW. Then parent's exceptions will be copyed to A's
whitelist. If copy failure occurs, just return leaving A to grant
permissions to all devices. And A may grant more permissions than
parent.

Backup A's whitelist and recover original exceptions after copy
failure.

Cc: stable@vger.kernel.org
Fixes: 4cef7299b478 ("device_cgroup: add proper checking when changing default behavior")
Signed-off-by: Wang Weiyang <wangweiyang2@huawei.com>
Reviewed-by: Aristeu Rozanski <aris@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index a9f8c63..bef2b92 100644 (file)
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -82,6 +82,17 @@ free_and_exit:
        return -ENOMEM;
 }
 
+static void dev_exceptions_move(struct list_head *dest, struct list_head *orig)
+{
+       struct dev_exception_item *ex, *tmp;
+
+       lockdep_assert_held(&devcgroup_mutex);
+
+       list_for_each_entry_safe(ex, tmp, orig, list) {
+               list_move_tail(&ex->list, dest);
+       }
+}
+
 /*
  * called under devcgroup_mutex
  */
@@ -604,11 +615,13 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
        int count, rc = 0;
        struct dev_exception_item ex;
        struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);
+       struct dev_cgroup tmp_devcgrp;
 
        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;
 
        memset(&ex, 0, sizeof(ex));
+       memset(&tmp_devcgrp, 0, sizeof(tmp_devcgrp));
        b = buffer;
 
        switch (*b) {
@@ -620,15 +633,27 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
 
                        if (!may_allow_all(parent))
                                return -EPERM;
-                       dev_exception_clean(devcgroup);
-                       devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
-                       if (!parent)
+                       if (!parent) {
+                               devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
+                               dev_exception_clean(devcgroup);
                                break;
+                       }
 
+                       INIT_LIST_HEAD(&tmp_devcgrp.exceptions);
+                       rc = dev_exceptions_copy(&tmp_devcgrp.exceptions,
+                                                &devcgroup->exceptions);
+                       if (rc)
+                               return rc;
+                       dev_exception_clean(devcgroup);
                        rc = dev_exceptions_copy(&devcgroup->exceptions,
                                                 &parent->exceptions);
-                       if (rc)
+                       if (rc) {
+                               dev_exceptions_move(&devcgroup->exceptions,
+                                                   &tmp_devcgrp.exceptions);
                                return rc;
+                       }
+                       devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
+                       dev_exception_clean(&tmp_devcgrp);
                        break;
                case DEVCG_DENY:
                        if (css_has_online_children(&devcgroup->css))