fscrypt: don't load ->i_crypt_info before it's known to be valid

In fscrypt_set_bio_crypt_ctx(), ->i_crypt_info isn't known to be
non-NULL until we check fscrypt_inode_uses_inline_crypto().  So, load
->i_crypt_info after the check rather than before.  This makes no
difference currently, but it prevents people from introducing bugs where
the pointer is dereferenced when it may be NULL.
Suggested-by: Dave Chinner <david@fromorbit.com>
Cc: Satya Tangirala <satyat@google.com>
Link: https://lore.kernel.org/r/20200727174158.121456-1-ebiggers@kernel.orgSigned-off-by: Eric Biggers <ebiggers@google.com>

fs/crypto/inline_crypt.c

@@ -244,11 +244,12 @@ static void fscrypt_generate_dun(const struct fscrypt_info *ci, u64 lblk_num,
 void fscrypt_set_bio_crypt_ctx(struct bio *bio, const struct inode *inode,
 			       u64 first_lblk, gfp_t gfp_mask)
 {
-	const struct fscrypt_info *ci = inode->i_crypt_info;
+	const struct fscrypt_info *ci;
 	u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
 
 	if (!fscrypt_inode_uses_inline_crypto(inode))
 		return;
+	ci = inode->i_crypt_info;
 
 	fscrypt_generate_dun(ci, first_lblk, dun);
 	bio_crypt_set_ctx(bio, &ci->ci_enc_key.blk_key->base, dun, gfp_mask);