[PATCH net 4/4] tls: fix use-after-free on failed backlog decryption

[Sabrina Dubroca <sd@queasysnail.net>]

When the decrypt request goes to the backlog and crypto_aead_decrypt
returns -EBUSY, tls_do_decryption will wait until all async
decryptions have completed. If one of them fails, tls_do_decryption
will return -EBADMSG and tls_decrypt_sg jumps to the error path,
releasing all the pages. But the pages have been passed to the async
callback, and have already been released by tls_decrypt_done.

The only true async case is when crypto_aead_decrypt returns
 -EINPROGRESS. With -EBUSY, we already waited so we can tell
tls_sw_recvmsg that the data is available for immediate copy, but we
need to notify tls_decrypt_sg (via the new ->async_done flag) that the
memory has already been released.

Fixes: 859054147318 ("net: tls: handle backlogging of crypto requests")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
---
 net/tls/tls_sw.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index 1fd37fe13ffd..211f57164cb6 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -52,6 +52,7 @@ struct tls_decrypt_arg {
 	struct_group(inargs,
 	bool zc;
 	bool async;
+	bool async_done;
 	u8 tail;
 	);
 
@@ -286,15 +287,18 @@ static int tls_do_decryption(struct sock *sk,
 	}
 
 	ret = crypto_aead_decrypt(aead_req);
+	if (ret == -EINPROGRESS)
+		return 0;
+
 	if (ret == -EBUSY) {
 		ret = tls_decrypt_async_wait(ctx);
-		ret = ret ?: -EINPROGRESS;
-	}
-	if (ret == -EINPROGRESS) {
-		return 0;
-	} else if (darg->async) {
-		atomic_dec(&ctx->decrypt_pending);
+		darg->async_done = true;
+		/* all completions have run, we're not doing async anymore */
+		darg->async = false;
+		return ret;
 	}
+
+	atomic_dec(&ctx->decrypt_pending);
 	darg->async = false;
 
 	return ret;
@@ -1593,8 +1597,11 @@ static int tls_decrypt_sg(struct sock *sk, struct iov_iter *out_iov,
 	/* Prepare and submit AEAD request */
 	err = tls_do_decryption(sk, sgin, sgout, dctx->iv,
 				data_len + prot->tail_size, aead_req, darg);
-	if (err)
+	if (err) {
+		if (darg->async_done)
+			goto exit_free_skb;
 		goto exit_free_pages;
+	}
 
 	darg->skb = clear_skb ?: tls_strp_msg(ctx);
 	clear_skb = NULL;
@@ -1606,6 +1613,9 @@ static int tls_decrypt_sg(struct sock *sk, struct iov_iter *out_iov,
 		return err;
 	}
 
+	if (unlikely(darg->async_done))
+		return 0;
+
 	if (prot->tail_size)
 		darg->tail = dctx->tail;
 
-- 
2.43.0