[PATCH 6.12 082/105] crypto: af_alg - Set merge to zero early in af_alg_sendmsg

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

6.12-stable review patch.  If anyone has any objections, please let me know.

------------------

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

[ Upstream commit 9574b2330dbd2b5459b74d3b5e9619d39299fc6f ]

If an error causes af_alg_sendmsg to abort, ctx->merge may contain
a garbage value from the previous loop.  This may then trigger a
crash on the next entry into af_alg_sendmsg when it attempts to do
a merge that can't be done.

Fix this by setting ctx->merge to zero near the start of the loop.

Fixes: 8ff590903d5 ("crypto: algif_skcipher - User-space interface for skcipher operations")
Reported-by: Muhammad Alifa Ramdhan <ramdhan@starlabs.sg>
Reported-by: Bing-Jhong Billy Jheng <billy@starlabs.sg>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 crypto/af_alg.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index f02c5586a8ab3..ca6fdcc6c54ac 100644
--- a/crypto/af_alg.c
+++ b/crypto/af_alg.c
@@ -1025,6 +1025,8 @@ int af_alg_sendmsg(struct socket *sock, struct msghdr *msg, size_t size,
 			continue;
 		}
 
+		ctx->merge = 0;
+
 		if (!af_alg_writable(sk)) {
 			err = af_alg_wait_for_wmem(sk, msg->msg_flags);
 			if (err)
@@ -1064,7 +1066,6 @@ int af_alg_sendmsg(struct socket *sock, struct msghdr *msg, size_t size,
 			ctx->used += plen;
 			copied += plen;
 			size -= plen;
-			ctx->merge = 0;
 		} else {
 			do {
 				struct page *pg;
-- 
2.51.0