From 11edb555966ed2c66c533d17c604f9d7e580a829 Mon Sep 17 00:00:00 2001
From: Stephan Mueller <smueller@chronox.de>
Date: Wed, 29 Nov 2017 12:02:23 +0100
Subject: [PATCH] crypto: af_alg - wait for data at beginning of recvmsg
Git-commit: 11edb555966ed2c66c533d17c604f9d7e580a829
Patch-mainline: v4.15-rc5
References: bsc#1154737

The wait for data is a non-atomic operation that can sleep and therefore
potentially release the socket lock. The release of the socket lock
allows another thread to modify the context data structure. The waiting
operation for new data therefore must be called at the beginning of
recvmsg. This prevents a race condition where checks of the members of
the context data structure are performed by recvmsg while there is a
potential for modification of these values.

Fixes: e870456d8e7c ("crypto: algif_skcipher - overhaul memory management")
Fixes: d887c52d6ae4 ("crypto: algif_aead - overhaul memory management")
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: <stable@vger.kernel.org> # v4.14+
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 crypto/af_alg.c         | 6 ------
 crypto/algif_aead.c     | 6 ++++++
 crypto/algif_skcipher.c | 6 ++++++
 3 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index 358749c38894..f1a2caf1b59b 100644
--- a/crypto/af_alg.c
+++ b/crypto/af_alg.c
@@ -1137,12 +1137,6 @@ int af_alg_get_rsgl(struct sock *sk, struct msghdr *msg, int flags,
 		if (!af_alg_readable(sk))
 			break;
 
-		if (!ctx->used) {
-			err = af_alg_wait_for_data(sk, flags);
-			if (err)
-				return err;
-		}
-
 		seglen = min_t(size_t, (maxsize - len),
 			       msg_data_left(msg));
 
diff --git a/crypto/algif_aead.c b/crypto/algif_aead.c
index 805f485ddf1b..c8a32bef208a 100644
--- a/crypto/algif_aead.c
+++ b/crypto/algif_aead.c
@@ -111,6 +111,12 @@ static int _aead_recvmsg(struct socket *sock, struct msghdr *msg,
 	size_t usedpages = 0;		/* [in]  RX bufs to be used from user */
 	size_t processed = 0;		/* [in]  TX bufs to be consumed */
 
+	if (!ctx->used) {
+		err = af_alg_wait_for_data(sk, flags);
+		if (err)
+			return err;
+	}
+
 	/*
 	 * Data length provided by caller via sendmsg/sendpage that has not
 	 * yet been processed.
diff --git a/crypto/algif_skcipher.c b/crypto/algif_skcipher.c
index 30cff827dd8f..6fb595cd63ac 100644
--- a/crypto/algif_skcipher.c
+++ b/crypto/algif_skcipher.c
@@ -72,6 +72,12 @@ static int _skcipher_recvmsg(struct socket *sock, struct msghdr *msg,
 	int err = 0;
 	size_t len = 0;
 
+	if (!ctx->used) {
+		err = af_alg_wait_for_data(sk, flags);
+		if (err)
+			return err;
+	}
+
 	/* Allocate cipher request for current operation. */
 	areq = af_alg_alloc_areq(sk, sizeof(struct af_alg_async_req) +
 				     crypto_skcipher_reqsize(tfm));
-- 
2.16.4