[PATCH] tpm: Move dereference after NULL check in tpm_buf_check_hmac_response

[Hao Ge]

From: Hao Ge <ge...@kylinos.cn>

We shouldn't dereference "auth" until after we have checked that it is
non-NULL.

Fixes: 7ca110f2679b ("tpm: Address !chip->auth in 
tpm_buf_append_hmac_session*()")
Signed-off-by: Hao Ge <ge...@kylinos.cn>
---
 drivers/char/tpm/tpm2-sessions.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
index 2281d55df545..d3521aadd43e 100644
--- a/drivers/char/tpm/tpm2-sessions.c
+++ b/drivers/char/tpm/tpm2-sessions.c
@@ -746,15 +746,16 @@ int tpm_buf_check_hmac_response(struct tpm_chip *chip, 
struct tpm_buf *buf,
        struct tpm2_auth *auth = chip->auth;
        off_t offset_s, offset_p;
        u8 rphash[SHA256_DIGEST_SIZE];
-       u32 attrs;
+       u32 attrs, cc;
        struct sha256_state sctx;
        u16 tag = be16_to_cpu(head->tag);
-       u32 cc = be32_to_cpu(auth->ordinal);
        int parm_len, len, i, handles;
 
        if (!auth)
                return rc;
 
+       cc = be32_to_cpu(auth->ordinal);
+
        if (auth->session >= TPM_HEADER_SIZE) {
                WARN(1, "tpm session not filled correctly\n");
                goto out;
-- 
2.25.1