[PATCH net 4/7] tls: rx: strp: fix determining record length in copy mode

[Jakub Kicinski <kuba@kernel.org>]

We call tls_rx_msg_size(skb) before doing skb->len += chunk.
So the tls_rx_msg_size() code will see old skb->len, most
likely leading to an over-read.

Worst case we will over read an entire record, next iteration
will try to trim the skb but may end up turning frag len negative
or discarding the subsequent record (since we already told TCP
we've read it during previous read but now we'll trim it out of
the skb).

Fixes: 84c61fe1a75b ("tls: rx: do not use the standard strparser")
Tested-by: Shai Amiram <samiram@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 net/tls/tls_strp.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/net/tls/tls_strp.c b/net/tls/tls_strp.c
index 2b6fa9855999..e2e48217e7ac 100644
--- a/net/tls/tls_strp.c
+++ b/net/tls/tls_strp.c
@@ -210,19 +210,28 @@ static int tls_strp_copyin(read_descriptor_t *desc, struct sk_buff *in_skb,
 					   skb_frag_size(frag),
 					   chunk));
 
-		sz = tls_rx_msg_size(strp, strp->anchor);
+		skb->len += chunk;
+		skb->data_len += chunk;
+		skb_frag_size_add(frag, chunk);
+
+		sz = tls_rx_msg_size(strp, skb);
 		if (sz < 0) {
 			desc->error = sz;
 			return 0;
 		}
 
 		/* We may have over-read, sz == 0 is guaranteed under-read */
-		if (sz > 0)
-			chunk =	min_t(size_t, chunk, sz - skb->len);
+		if (unlikely(sz && sz < skb->len)) {
+			int over = skb->len - sz;
+
+			WARN_ON_ONCE(over > chunk);
+			skb->len -= over;
+			skb->data_len -= over;
+			skb_frag_size_add(frag, -over);
+
+			chunk -= over;
+		}
 
-		skb->len += chunk;
-		skb->data_len += chunk;
-		skb_frag_size_add(frag, chunk);
 		frag++;
 		len -= chunk;
 		offset += chunk;
-- 
2.40.1