netdev - [PATCH] crypto: algif/hash: Fix race between MORE and non-MORE sends

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Date: Fri, 07 Jul 2023 10:12:38 +0100
From: David Howells <dhowells@...hat.com>
To: Herbert Xu <herbert@...dor.apana.org.au>
cc: dhowells@...hat.com,
    syzbot <syzbot+689ec3afb1ef07b766b2@...kaller.appspotmail.com>,
    Paolo Abeni <pabeni@...hat.com>,
    "David S. Miller" <davem@...emloft.net>,
    Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
    linux-crypto@...r.kernel.org, netdev@...r.kernel.org,
    linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] crypto: algif/hash: Fix race between MORE and non-MORE sends

The 'MSG_MORE' state of the previous sendmsg() is fetched without the
socket lock held, so two sendmsg calls can race.  This can be seen with a
large sendfile() as that now does a series of sendmsg() calls, and if a
write() comes in on the same socket at an inopportune time, it can flip the
state.

Fix this by moving the fetch of ctx->more inside the socket lock.

Fixes: c662b043cdca ("crypto: af_alg/hash: Support MSG_SPLICE_PAGES")
Reported-by: syzbot+689ec3afb1ef07b766b2@...kaller.appspotmail.com
Link: https://lore.kernel.org/r/000000000000554b8205ffdea64e@google.com/
Signed-off-by: David Howells <dhowells@...hat.com>
Tested-by: syzbot+689ec3afb1ef07b766b2@...kaller.appspotmail.com
cc: Herbert Xu <herbert@...dor.apana.org.au>
cc: Paolo Abeni <pabeni@...hat.com>
cc: "David S. Miller" <davem@...emloft.net>
cc: Eric Dumazet <edumazet@...gle.com>
cc: Jakub Kicinski <kuba@...nel.org>
cc: linux-crypto@...r.kernel.org
cc: netdev@...r.kernel.org
---
 crypto/algif_hash.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/crypto/algif_hash.c b/crypto/algif_hash.c
index 0ab43e149f0e..82c44d4899b9 100644
--- a/crypto/algif_hash.c
+++ b/crypto/algif_hash.c
@@ -68,13 +68,15 @@ static int hash_sendmsg(struct socket *sock, struct msghdr *msg,
 	struct hash_ctx *ctx = ask->private;
 	ssize_t copied = 0;
 	size_t len, max_pages, npages;
-	bool continuing = ctx->more, need_init = false;
+	bool continuing, need_init = false;
 	int err;
 
 	max_pages = min_t(size_t, ALG_MAX_PAGES,
 			  DIV_ROUND_UP(sk->sk_sndbuf, PAGE_SIZE));
 
 	lock_sock(sk);
+	continuing = ctx->more;
+
 	if (!continuing) {
 		/* Discard a previous request that wasn't marked MSG_MORE. */
 		hash_free_result(sk, ctx);