userns: prevent speculative execution

CVE-2017-5753
CVE-2017-5715

Real commit text tbd

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
(cherry picked from commit bf5352bb462ac0acf4ebca109e964666f845bd54)
Signed-off-by: Andy Whitcroft <apw@canonical.com>

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 23b4d6ec05d77af77be77ea5efc9097325f8d4ea..7bbbfa31156fe9db23fd7749608645dedd757f40 100644 (file)
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -502,8 +502,10 @@ static void *m_start(struct seq_file *seq, loff_t *ppos,
        struct uid_gid_extent *extent = NULL;
        loff_t pos = *ppos;
 
-       if (pos < map->nr_extents)
+       if (pos < map->nr_extents) {
+               gmb();
                extent = &map->extent[pos];
+       }
 
        return extent;
 }