[PATCH] net/tls: move version check after second userspace fetch

[PATCH] net/tls: move version check after second userspace fetch

[Meng Xu]

Even the userspace buffer optval passed the version check
(i.e., tmp_crypto_info.version == TLS_1_2_VERSION) after the first fetch,
it can still be changed before the second copy_from_user() and hence,
a version different than TLS_1_2_VERSION may be copied into crypto_info.
This patch moves the version check after the second userspace fetch.

Signed-off-by: Meng Xu <mengxu.gatech@gmail.com>
---
 net/tls/tls_main.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/net/tls/tls_main.c b/net/tls/tls_main.c
index 60aff60..d4a7bc6 100644
--- a/net/tls/tls_main.c
+++ b/net/tls/tls_main.c
@@ -354,12 +354,6 @@ static int do_tls_setsockopt_tx(struct sock *sk, char __user *optval,
 		goto out;
 	}
 
-	/* check version */
-	if (tmp_crypto_info.version != TLS_1_2_VERSION) {
-		rc = -ENOTSUPP;
-		goto out;
-	}
-
 	/* get user crypto info */
 	crypto_info = &ctx->crypto_send;
 
@@ -382,6 +376,12 @@ static int do_tls_setsockopt_tx(struct sock *sk, char __user *optval,
 			rc = -EFAULT;
 			goto err_crypto_info;
 		}
+
+		/* check version */
+		if (crypto_info->version != TLS_1_2_VERSION) {
+			rc = -ENOTSUPP;
+			goto err_crypto_info;
+		}
 		break;
 	}
 	default:
-- 
2.7.4

Re: [PATCH] net/tls: move version check after second userspace fetch

[David Miller]

From: Meng Xu <mengxu.gatech@gmail.com>
Date: Sun, 24 Sep 2017 11:14:55 -0400

> @@ -382,6 +376,12 @@ static int do_tls_setsockopt_tx(struct sock *sk, char __user *optval,
>  			rc = -EFAULT;
>  			goto err_crypto_info;
>  		}
> +
> +		/* check version */
> +		if (crypto_info->version != TLS_1_2_VERSION) {
> +			rc = -ENOTSUPP;
> +			goto err_crypto_info;
> +		}
>  		break;
>  	}
>  	default:
> -- 
> 2.7.4
> 

Please, again, deduce this into a single userspace copy.  Otherwise we're going to
add this check for every cipher we add new support for.

Copy the on-stack crypto info ("tmp_crypto_info") into 'crypto_info' and then
bring in from userspace any further bytes that need to be copied.

That guarantees that the version will not change, and the existing check can
stay where it is.