linux-kernel - [PATCH v2] tpm: Move dereference after NULL check in tpm_buf_check_hmac

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Message-Id: <20240715072428.474760-1-hao.ge@linux.dev>
Date: Mon, 15 Jul 2024 15:24:28 +0800
From: Hao Ge <hao.ge@...ux.dev>
To: jarkko@...nel.org
Cc: gehao@...inos.cn,
	hao.ge@...ux.dev,
	jgg@...pe.ca,
	linux-integrity@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	peterhuewe@....de
Subject: [PATCH v2] tpm: Move dereference after NULL check in tpm_buf_check_hmac_response

From: Hao Ge <gehao@...inos.cn>

Smatch static checker reported below warning:

    drivers/char/tpm/tpm2-sessions.c:755 tpm_buf_check_hmac_response()
    warn: variable dereferenced before check 'auth' (see line 752)

Move dereference "auth" after we have checked that it is
non-NULL.

Fixes: 1085b8276bb4 ("tpm: Add the rest of the session HMAC API")
Signed-off-by: Hao Ge <gehao@...inos.cn>
---
v2:
- adjust title and Fixes commit
---
 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