From: Sabrina Dubroca <sd@queasysnail.net>
To: Jakub Kicinski <kuba@kernel.org>,
Herbert Xu <herbert@gondor.apana.org.au>
Cc: netdev@vger.kernel.org, Dave Watson <davejwatson@fb.com>,
Vakul Garg <vakul.garg@nxp.com>,
Boris Pismenny <borisp@nvidia.com>,
John Fastabend <john.fastabend@gmail.com>
Subject: Re: [PATCH net 5/5] tls: don't decrypt the next record if it's of a different type
Date: Thu, 7 Sep 2023 14:21:59 +0200 [thread overview]
Message-ID: <ZPm__x5TcsmqagBH@hog> (raw)
In-Reply-To: <20230906204727.08a79e00@kernel.org>
2023-09-06, 20:47:27 -0700, Jakub Kicinski wrote:
> On Wed, 6 Sep 2023 19:08:35 +0200 Sabrina Dubroca wrote:
> > If the next record is of a different type, we won't copy it to
> > userspace in this round, tls_record_content_type will stop us just
> > after decryption. Skip decryption until the next recvmsg() call.
> >
> > This fixes a use-after-free when a data record is decrypted
> > asynchronously but doesn't fill the userspace buffer, and the next
> > record is non-data, for example in the bad_cmsg selftest.
>
> What's the UAF on?
It doesn't always happen unless I set cryptd_delay_ms from my debug
patch (10 is enough):
https://patchwork.kernel.org/project/linux-crypto/patch/9d664093b1bf7f47497b2c40b3a085b45f3274a2.1694021240.git.sd@queasysnail.net/
UAF is on the crypto_async_request (part of the aead_request,
allocated in the big kmalloc in tls_decrypt_sg), mostly caught when
cryptd_queue_worker calls crypto_request_complete, but sometimes a bit
earlier (in crypto_dequeue_request).
I'll admit this patch is papering over the issue a bit, but decrypting
a record we know we won't read within this recv() call seems a bit
pointless.
I wonder if the way we're using ctx->async_wait here is correct. I'm
observing crypto_wait_req return 0 even though the decryption hasn't
run yet (and it should return -EBADMSG, not 0). I guess
tls_decrypt_done calls the completion (since we only had one
decrypt_pending), and then crypto_wait_req thinks everything is
already done.
Adding a fresh crypto_wait in tls_do_decryption (DECLARE_CRYPTO_WAIT)
and using it in the !darg->async case also seems to fix the UAF (but
makes the bad_cmsg test case fail in the same way as what I wrote in
the cover letter for bad_in_large_read -- not decrypting the next
message at all makes the selftest pass).
Herbert, WDYT? We're calling tls_do_decryption twice from the same
tls_sw_recvmsg invocation, first with darg->async = true, then with
darg->async = false. Is it ok to use ctx->async_wait for both, or do
we need a fresh one as in this patch?
-------- 8< --------
diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index 86b835b15872..ad51960f2864 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -246,6 +246,7 @@ static int tls_do_decryption(struct sock *sk,
struct tls_context *tls_ctx = tls_get_ctx(sk);
struct tls_prot_info *prot = &tls_ctx->prot_info;
struct tls_sw_context_rx *ctx = tls_sw_ctx_rx(tls_ctx);
+ DECLARE_CRYPTO_WAIT(wait);
int ret;
aead_request_set_tfm(aead_req, ctx->aead_recv);
@@ -262,7 +263,7 @@ static int tls_do_decryption(struct sock *sk,
} else {
aead_request_set_callback(aead_req,
CRYPTO_TFM_REQ_MAY_BACKLOG,
- crypto_req_done, &ctx->async_wait);
+ crypto_req_done, &wait);
}
ret = crypto_aead_decrypt(aead_req);
@@ -270,7 +271,7 @@ static int tls_do_decryption(struct sock *sk,
if (darg->async)
return 0;
- ret = crypto_wait_req(ret, &ctx->async_wait);
+ ret = crypto_wait_req(ret, &wait);
}
darg->async = false;
--
Sabrina
next prev parent reply other threads:[~2023-09-07 15:40 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-06 17:08 [PATCH net 0/5] tls: fix some issues with async encryption Sabrina Dubroca
2023-09-06 17:08 ` [PATCH net 1/5] net: tls: handle -EBUSY on async encrypt/decrypt requests Sabrina Dubroca
2023-09-07 1:50 ` Jakub Kicinski
2023-09-07 15:11 ` Simon Horman
2023-09-08 6:10 ` Herbert Xu
2023-09-08 15:55 ` Sabrina Dubroca
2023-09-08 21:26 ` Jakub Kicinski
2023-09-09 0:53 ` Herbert Xu
2023-09-12 4:43 ` Herbert Xu
2023-09-12 15:37 ` Sabrina Dubroca
2023-09-14 9:00 ` Herbert Xu
2023-09-06 17:08 ` [PATCH net 2/5] tls: fix use-after-free with partial reads and async decrypt Sabrina Dubroca
2023-09-07 2:05 ` Jakub Kicinski
2023-09-07 13:56 ` Sabrina Dubroca
2023-09-06 17:08 ` [PATCH net 3/5] tls: fix returned read length with async !zc decrypt Sabrina Dubroca
2023-09-06 17:08 ` [PATCH net 4/5] tls: fix race condition in async decryption of corrupted records Sabrina Dubroca
2023-09-06 17:08 ` [PATCH net 5/5] tls: don't decrypt the next record if it's of a different type Sabrina Dubroca
2023-09-07 3:47 ` Jakub Kicinski
2023-09-07 12:21 ` Sabrina Dubroca [this message]
2023-09-07 17:08 ` Jakub Kicinski
2023-09-08 6:06 ` Herbert Xu
2023-09-08 15:38 ` Sabrina Dubroca
2023-09-12 4:38 ` Herbert Xu
2023-09-13 13:25 ` Sabrina Dubroca
2023-09-14 9:45 ` Herbert Xu
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