FAILED: patch "[PATCH] crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 1b34cbbf4f011a121ef7b2d7d6e6920a036d5285
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025092107-crowbar-posting-c6ba@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 1b34cbbf4f011a121ef7b2d7d6e6920a036d5285 Mon Sep 17 00:00:00 2001
From: Herbert Xu <[email protected]>
Date: Tue, 16 Sep 2025 17:20:59 +0800
Subject: [PATCH] crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg

Issuing two writes to the same af_alg socket is bogus as the data will be interleaved in an unpredictable fashion. Furthermore, concurrent writes may create inconsistencies in the internal socket state.

Disallow this by adding a new ctx->write field that indiciates exclusive ownership for writing.

index 407f2c238f2c..ca6fdcc6c54a 100644
@@ -970,6 +970,12 @@ int af_alg_sendmsg(struct socket *sock, struct msghdr *msg, size_t size,
 	}
 
 	lock_sock(sk);
+	if (ctx->write) {
+		release_sock(sk);
+		return -EBUSY;
+	}
+	ctx->write = true;
+
 	if (ctx->init && !ctx->more) {
 		if (ctx->used) {
 			err = -EINVAL;

@@ -1105,6 +1111,7 @@ int af_alg_sendmsg(struct socket *sock, struct msghdr *msg, size_t size,
 
 unlock:
 	af_alg_data_wakeup(sk);
+	ctx->write = false;
 	release_sock(sk);
 
 	return copied ?: err;

index f7b3b93f3a49..0c70f3a55575 100644
@@ -135,6 +135,7 @@ struct af_alg_async_req {
  *			SG?
  * @enc:		Cryptographic operation to be performed when
  *			recvmsg is invoked.
+ * @write:		True if we are in the middle of a write.
  * @init:		True if metadata has been sent.
  * @len:		Length of memory allocated for this data structure.
  * @inflight:		Non-zero when AIO requests are in flight.

@@ -151,10 +152,11 @@ struct af_alg_ctx {
 	size_t used;
 	atomic_t rcvused;
 
-	bool more;
-	bool merge;
-	bool enc;
-	bool init;
+	u32		more:1,
+			merge:1,
+			enc:1,
+			write:1,
+			init:1;
 
 	unsigned int len;