KEYS: user: Align the payload buffer [Linux 5.0]

KEYS: user: Align the payload buffer [Linux 5.0]

This Linux kernel change "KEYS: user: Align the payload buffer" is included in the Linux 5.0 release. This change is authored by Eric Biggers <ebiggers [at] google.com> on Wed Feb 20 13:32:11 2019 +0000. The commit for this change in Linux stable tree is cc1780f (patch).

KEYS: user: Align the payload buffer

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 <[email protected]>
Fixes: 2aa349f6e37c ("[PATCH] Keys: Export user-defined keyring operations")
Fixes: 88bd6ccdcdd6 ("ext4 crypto: add encryption key management facilities")
Cc: [email protected]
Signed-off-by: Eric Biggers <[email protected]>
Tested-by: Aaro Koskinen <[email protected]>
Signed-off-by: David Howells <[email protected]>
Signed-off-by: James Morris <[email protected]>

There are 2 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 include/keys/user-type.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/keys/user-type.h b/include/keys/user-type.h
index e098cbe..12babe9 100644
--- a/include/keys/user-type.h
+++ b/include/keys/user-type.h
@@ -31,7 +31,7 @@
 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;

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