mac80211_hwsim: Fix possible Spectre-v1 for hwsim_world_regdom_custom

User controls @idx which to be used as index of hwsim_world_regdom_custom.
So, It can be exploited via Spectre-like attack. (speculative execution)

This kind of attack leaks address of hwsim_world_regdom_custom,
It leads an attacker to bypass security mechanism such as KASLR.

So sanitize @idx before using it to prevent attack.

I leveraged strategy [1] to find and exploit this gadget.

[1] https://github.com/jinb-park/linux-exploit/tree/master/exploit-remaining-spectre-gadget/

Signed-off-by: Jinbum Park <jinb.park7@gmail.com>
[johannes: unwrap URL]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/drivers/net/wireless/mac80211_hwsim.c b/drivers/net/wireless/mac80211_hwsim.c
index 7d0b460868f91024c7faac67ae00301cbf2ca01e..80e2c8595c7c8d63da25cd245357d15acce4635b 100644 (file)
--- a/drivers/net/wireless/mac80211_hwsim.c
+++ b/drivers/net/wireless/mac80211_hwsim.c
@@ -33,6 +33,7 @@
 #include <net/net_namespace.h>
 #include <net/netns/generic.h>
 #include <linux/rhashtable.h>
+#include <linux/nospec.h>
 #include "mac80211_hwsim.h"
 
 #define WARN_QUEUE 100
@@ -3229,6 +3230,9 @@ static int hwsim_new_radio_nl(struct sk_buff *msg, struct genl_info *info)
                        kfree(hwname);
                        return -EINVAL;
                }
+
+               idx = array_index_nospec(idx,
+                                        ARRAY_SIZE(hwsim_world_regdom_custom));
                param.regd = hwsim_world_regdom_custom[idx];
        }