linux-kernel - [PATCH 3.16 169/202] KEYS: user: Align the payload buffer

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Message-ID: <lsq.1556377989.249665964@decadent.org.uk>
Date:   Sat, 27 Apr 2019 16:13:09 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "James Morris" <james.morris@...rosoft.com>,
        "Eric Biggers" <ebiggers@...gle.com>,
        "David Howells" <dhowells@...hat.com>,
        "Aaro Koskinen" <aaro.koskinen@....fi>
Subject: [PATCH 3.16 169/202] KEYS: user: Align the payload buffer

3.16.66-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Eric Biggers <ebiggers@...gle.com>

commit cc1780fc42c76c705dd07ea123f1143dc5057630 upstream.

Align the payload of "user" and "logon" keys so that users of the
keyrings service can access it as a struct that requires more than
2-byte alignment.  fscrypt currently does this which results in the read
of fscrypt_key::size being misaligned as it needs 4-byte alignment.

Align to __alignof__(u64) rather than __alignof__(long) since in the
future it's conceivable that people would use structs beginning with
u64, which on some platforms would require more than 'long' alignment.

Reported-by: Aaro Koskinen <aaro.koskinen@....fi>
Fixes: 2aa349f6e37c ("[PATCH] Keys: Export user-defined keyring operations")
Fixes: 88bd6ccdcdd6 ("ext4 crypto: add encryption key management facilities")
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
Tested-by: Aaro Koskinen <aaro.koskinen@....fi>
Signed-off-by: David Howells <dhowells@...hat.com>
Signed-off-by: James Morris <james.morris@...rosoft.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 include/keys/user-type.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/keys/user-type.h
+++ b/include/keys/user-type.h
@@ -29,7 +29,7 @@
 struct user_key_payload {
 	struct rcu_head	rcu;		/* RCU destructor */
 	unsigned short	datalen;	/* length of this data */
-	char		data[0];	/* actual data */
+	char		data[0] __aligned(__alignof__(u64)); /* actual data */
 };
 
 extern struct key_type key_type_user;