[PATCH] can: af_can: Fix Spectre v1 vulnerability

[PATCH] can: af_can: Fix Spectre v1 vulnerability

[Gustavo A. R. Silva]

protocol is indirectly controlled by user-space, hence leading to
a potential exploitation of the Spectre variant 1 vulnerability.

This issue was detected with the help of Smatch:

net/can/af_can.c:115 can_get_proto() warn: potential spectre issue 'proto_tab' [w]

Fix this by sanitizing protocol before using it to index proto_tab.

Notice that given that speculation windows are large, the policy is
to kill the speculation on the first load and not worry if it can be
completed with a dependent load/store [1].

[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 net/can/af_can.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/can/af_can.c b/net/can/af_can.c
index 1684ba5b51eb..cade7250c6d4 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -59,6 +59,7 @@
 #include <linux/can/core.h>
 #include <linux/can/skb.h>
 #include <linux/ratelimit.h>
+#include <linux/nospec.h>
 #include <net/net_namespace.h>
 #include <net/sock.h>
 
@@ -136,6 +137,7 @@ static int can_create(struct net *net, struct socket *sock, int protocol,
 
 	if (protocol < 0 || protocol >= CAN_NPROTO)
 		return -EINVAL;
+	protocol = array_index_nospec(protocol, CAN_NPROTO);
 
 	cp = can_get_proto(protocol);
 
-- 
2.20.1

Re: [PATCH] can: af_can: Fix Spectre v1 vulnerability

[Oliver Hartkopp]

After *trying* to follow the discussion on ...

https://marc.info/?l=linux-kernel&m=154554485324143&w=2
[PATCH] net: core: Fix Spectre v1 vulnerability

... I'm still not sure whether af_can.c needs this enhancement or not.

Just waiting for the end of the discussion :-)

Thanks to the experts!

Oliver

On 12/21/18 10:22 PM, Gustavo A. R. Silva wrote:
> protocol is indirectly controlled by user-space, hence leading to
> a potential exploitation of the Spectre variant 1 vulnerability.
> 
> This issue was detected with the help of Smatch:
> 
> net/can/af_can.c:115 can_get_proto() warn: potential spectre issue 'proto_tab' [w]
> 
> Fix this by sanitizing protocol before using it to index proto_tab.
> 
> Notice that given that speculation windows are large, the policy is
> to kill the speculation on the first load and not worry if it can be
> completed with a dependent load/store [1].
> 
> [1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> ---
>   net/can/af_can.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/net/can/af_can.c b/net/can/af_can.c
> index 1684ba5b51eb..cade7250c6d4 100644
> --- a/net/can/af_can.c
> +++ b/net/can/af_can.c
> @@ -59,6 +59,7 @@
>   #include <linux/can/core.h>
>   #include <linux/can/skb.h>
>   #include <linux/ratelimit.h>
> +#include <linux/nospec.h>
>   #include <net/net_namespace.h>
>   #include <net/sock.h>
>   
> @@ -136,6 +137,7 @@ static int can_create(struct net *net, struct socket *sock, int protocol,
>   
>   	if (protocol < 0 || protocol >= CAN_NPROTO)
>   		return -EINVAL;
> +	protocol = array_index_nospec(protocol, CAN_NPROTO);
>   
>   	cp = can_get_proto(protocol);
>   
>