[PATCH net v2] tls: fix the open record check in the max payload size setsockopt

[Jiayuan Chen <jiayuan.chen@linux.dev>]

do_tls_setsockopt_tx_payload_len() refuses to resize records while one is
open, but the check is broken in two ways.

It reaches for the open record through tls_sw_ctx_tx(), an unchecked cast
of ctx->priv_ctx_tx.  Under device offload that pointer is a
tls_offload_context_tx, so the check reads a field of the wrong struct: it
returns EBUSY on whatever happens to be there, and never sees the record
that really is open.  Dispatch on tx_conf.

The socket lock alone is also not enough to tell no sender is in flight.
The device tx path drops it in sk_stream_wait_memory() after
tls_push_record() cleared open_record, so setsockopt can slip in
mid-sendmsg and shrink the limit.  tls_push_data() latches the limit once
per call, and a record left open by MSG_MORE can then be bigger than the
new limit, making the u32 subtraction in the copy clamp wrap around and
build an oversized record.  Take tx_lock like the sendmsg paths do so
setsockopt waits for in-flight senders.  Re-reading the limit inside the
tls_push_data() loop could close the wrap too, but a parked sender would
still finish with the old limit, so serializing on tx_lock is simpler.

Fixes: 82cb5be6ad64 ("net/tls: support setting the maximum payload size")
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
---
v1 -> v2:
  - also take tx_lock in setsockopt, the socket lock alone can't stop a
    device sender parked in sk_stream_wait_memory() (AI review on v1)
v1: https://lore.kernel.org/netdev/20260831025607.62927-1-jiayuan.chen@linux.dev/

base on my netdevsim + tls (in progress)
https://lore.kernel.org/netdev/20260728125658.390500-1-jiayuan.chen@linux.dev/

Previous finding:
b17cf742eaad ("tls: device: fix out-of-bounds write in tls_append_frag()")
---
 net/tls/tls_main.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/net/tls/tls_main.c b/net/tls/tls_main.c
index fbb274287aa5..114e5113bafd 100644
--- a/net/tls/tls_main.c
+++ b/net/tls/tls_main.c
@@ -833,15 +833,29 @@ static int do_tls_setsockopt_no_pad(struct sock *sk, sockptr_t optval,
 	return rc;
 }
 
+/* priv_ctx_tx holds a different structure on each TX path, so tx_conf has to
+ * say which open record to look at.
+ */
+static bool tls_tx_record_is_open(struct tls_context *ctx)
+{
+	switch (ctx->tx_conf) {
+	case TLS_SW:
+		return !!tls_sw_ctx_tx(ctx)->open_rec;
+	case TLS_HW:
+		return !!tls_offload_ctx_tx(ctx)->open_record;
+	default:
+		return false;
+	}
+}
+
 static int do_tls_setsockopt_tx_payload_len(struct sock *sk, sockptr_t optval,
 					    unsigned int optlen)
 {
 	struct tls_context *ctx = tls_get_ctx(sk);
-	struct tls_sw_context_tx *sw_ctx = tls_sw_ctx_tx(ctx);
 	u16 value;
 	bool tls_13 = ctx->prot_info.version == TLS_1_3_VERSION;
 
-	if (sw_ctx && sw_ctx->open_rec)
+	if (tls_tx_record_is_open(ctx))
 		return -EBUSY;
 
 	if (sockptr_is_null(optval) || optlen != sizeof(value))
@@ -862,6 +876,7 @@ static int do_tls_setsockopt_tx_payload_len(struct sock *sk, sockptr_t optval,
 static int do_tls_setsockopt(struct sock *sk, int optname, sockptr_t optval,
 			     unsigned int optlen)
 {
+	struct tls_context *ctx;
 	int rc = 0;
 
 	switch (optname) {
@@ -881,9 +896,17 @@ static int do_tls_setsockopt(struct sock *sk, int optname, sockptr_t optval,
 		rc = do_tls_setsockopt_no_pad(sk, optval, optlen);
 		break;
 	case TLS_TX_MAX_PAYLOAD_LEN:
+		/* Take tx_lock like the sendmsg paths do, the socket lock is
+		 * dropped while a sender waits for memory, with no record open.
+		 */
+		ctx = tls_get_ctx(sk);
+		rc = mutex_lock_interruptible(&ctx->tx_lock);
+		if (rc)
+			break;
 		lock_sock(sk);
 		rc = do_tls_setsockopt_tx_payload_len(sk, optval, optlen);
 		release_sock(sk);
+		mutex_unlock(&ctx->tx_lock);
 		break;
 	default:
 		rc = -ENOPROTOOPT;
-- 
2.43.0