[SRU][F][PATCH 3/3] tls: fix use-after-free on failed backlog decryption

[Juerg Haefliger]

From: Sabrina Dubroca <sd at 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 at queasysnail.net>
Link: https://lore.kernel.org/r/4755dd8d9bebdefaa19ce1439b833d6199d4364c.1709132643.git.sd@queasysnail.net
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
(backported from commit 13114dc5543069f7b97991e3b79937b6da05f5b0)
[juergh: Adjusted context and 'return err' instead of 'goto exit_free_skb'
 due to missing commits:
 fd31f3996af2 ("tls: rx: decrypt into a fresh skb")
 6bd116c8c654 ("tls: rx: return the decrypted skb via darg")]
CVE-2024-26800
Signed-off-by: Juerg Haefliger <juerg.haefliger at canonical.com>
---
 net/tls/tls_sw.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index c91a057b35a8..848df765bc17 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -47,6 +47,7 @@
 struct tls_decrypt_arg {
 	bool zc;
 	bool async;
+	bool async_done;
 };
 
 noinline void tls_err_abort(struct sock *sk, int err)
@@ -287,15 +288,18 @@ 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;
@@ -1551,9 +1555,17 @@ static int decrypt_internal(struct sock *sk, struct sk_buff *skb,
 	/* Prepare and submit AEAD request */
 	err = tls_do_decryption(sk, skb, sgin, sgout, iv,
 				data_len, aead_req, darg);
+	if (err) {
+		if (darg->async_done)
+			return err;
+	}
+
 	if (darg->async)
 		return 0;
 
+	if (unlikely(darg->async_done))
+		return 0;
+
 	/* Release the pages in case iov was mapped to pages */
 	for (; pages > 0; pages--)
 		put_page(sg_page(&sgout[pages]));
-- 
2.43.0