security: keys: perform capable check only on privileged operations

If the current task fails the check for the queried capability via
`capable(CAP_SYS_ADMIN)` LSMs like SELinux generate a denial message.
Issuing such denial messages unnecessarily can lead to a policy author
granting more privileges to a subject than needed to silence them.

Reorder CAP_SYS_ADMIN checks after the check whether the operation is
actually privileged.

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index d54f73c558f721fc29dd0220e175a65208880188..19be69fa4d052a6a47e331e9100cc5eeecb4f384 100644 (file)
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -980,14 +980,19 @@ long keyctl_chown_key(key_serial_t id, uid_t user, gid_t group)
        ret = -EACCES;
        down_write(&key->sem);
 
-       if (!capable(CAP_SYS_ADMIN)) {
+       {
+               bool is_privileged_op = false;
+
                /* only the sysadmin can chown a key to some other UID */
                if (user != (uid_t) -1 && !uid_eq(key->uid, uid))
-                       goto error_put;
+                       is_privileged_op = true;
 
                /* only the sysadmin can set the key's GID to a group other
                 * than one of those that the current process subscribes to */
                if (group != (gid_t) -1 && !gid_eq(gid, key->gid) && !in_group_p(gid))
+                       is_privileged_op = true;
+
+               if (is_privileged_op && !capable(CAP_SYS_ADMIN))
                        goto error_put;
        }
 
@@ -1088,7 +1093,7 @@ long keyctl_setperm_key(key_serial_t id, key_perm_t perm)
        down_write(&key->sem);
 
        /* if we're not the sysadmin, we can only change a key that we own */
-       if (capable(CAP_SYS_ADMIN) || uid_eq(key->uid, current_fsuid())) {
+       if (uid_eq(key->uid, current_fsuid()) || capable(CAP_SYS_ADMIN)) {
                key->perm = perm;
                notify_key(key, NOTIFY_KEY_SETATTR, 0);
                ret = 0;