Subject: [PATCH 26/27] net/tls: don't copy negative amounts of data in reencrypt

From: Jakub Kicinski <[email-masked]>
Date: Thu, 25 Apr 2019 17:35:09 -0700

[ Upstream commit 97e1caa517e22d62a283b876fb8aa5f4672c83dd ]

There is no guarantee the record starts before the skb frags.
If we don't check for this condition copy amount will get
negative, leading to reads and writes to random memory locations.
Familiar hilarity ensues.

Fixes: 4799ac81e52a ("tls: Add rx inline crypto offload")
Signed-off-by: Jakub Kicinski <[email-masked]>
Reviewed-by: John Hurley <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/tls/tls_device.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/net/tls/tls_device.c b/net/tls/tls_device.c
index 5f1d937c4be9..4068101d43ea 100644
--- a/net/tls/tls_device.c
+++ b/net/tls/tls_device.c
@@ -610,14 +610,16 @@ static int tls_device_reencrypt(struct sock *sk, struct sk_buff *skb)
 	else
 		err = 0;
 
-	copy = min_t(int, skb_pagelen(skb) - offset,
-		     rxm->full_len - TLS_CIPHER_AES_GCM_128_TAG_SIZE);
+	if (skb_pagelen(skb) > offset) {
+		copy = min_t(int, skb_pagelen(skb) - offset,
+			     rxm->full_len - TLS_CIPHER_AES_GCM_128_TAG_SIZE);
 
-	if (skb->decrypted)
-		skb_store_bits(skb, offset, buf, copy);
+		if (skb->decrypted)
+			skb_store_bits(skb, offset, buf, copy);
 
-	offset += copy;
-	buf += copy;
+		offset += copy;
+		buf += copy;
+	}
 
 	skb_walk_frags(skb, skb_iter) {
 		copy = min_t(int, skb_iter->len,
-- 
2.20.1