[SRU][J/N/P][PATCH 1/2] crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg

[Ian Whitfield]

From: Herbert Xu <herbert at gondor.apana.org.au>

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.

Fixes: 8ff590903d5 ("crypto: algif_skcipher - User-space interface for skcipher operations")
Reported-by: Muhammad Alifa Ramdhan <ramdhan at starlabs.sg>
Reported-by: Bing-Jhong Billy Jheng <billy at starlabs.sg>
Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>
(cherry picked from commit 1b34cbbf4f011a121ef7b2d7d6e6920a036d5285)
CVE-2025-39964
Signed-off-by: Ian Whitfield <ian.whitfield at canonical.com>
---
 crypto/af_alg.c         |  7 +++++++
 include/crypto/if_alg.h | 10 ++++++----
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index 0da7c1ac778a..f02c5586a8ab 100644
--- a/crypto/af_alg.c
+++ b/crypto/af_alg.c
@@ -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;
@@ -1104,6 +1110,7 @@ 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;
diff --git a/include/crypto/if_alg.h b/include/crypto/if_alg.h
index f7b3b93f3a49..0c70f3a55575 100644
--- a/include/crypto/if_alg.h
+++ b/include/crypto/if_alg.h
@@ -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;
 
-- 
2.43.0