[PATCH] tpm: tpm2_probe: propagate transport errors

[A. Sverdlin]

From: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>

tpm2_probe() reads the protocol version from the response tag and is
documented to return -errno on failure, but it always returns 0.  A
transport error (tpm_transmit_cmd() < 0) is thus swallowed together with
the intentionally ignored TPM response code, leaving TPM_CHIP_FLAG_TPM2
unset. A transient bus failure on the first command then misdetects a
TPM 2.0 as a 1.2 and the probe fails on the TPM 1.2 path:

  tpm_tis_i2c 0-002e: 1.2 TPM (device-id 0x1C, rev-id 22)
  tpm tpm0: A TPM error (-62) occurred attempting to determine the timeouts

Return the transport error instead; rc >= 0 still means a valid header was
received and the TPM's own response code is still ignored.

Fixes: 94e266ba1fa3 ("tpm: migrate tpm2_probe() to use struct tpm_buf")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
---
 drivers/char/tpm/tpm2-cmd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index a94f4395c198a..4b2bb2ddc321a 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -483,8 +483,9 @@ int tpm2_probe(struct tpm_chip *chip)
 		out = (struct tpm_header *)buf->data;
 		if (be16_to_cpu(out->tag) == TPM2_ST_NO_SESSIONS)
 			chip->flags |= TPM_CHIP_FLAG_TPM2;
+		return 0;
 	}
-	return 0;
+	return rc;
 }
 EXPORT_SYMBOL_GPL(tpm2_probe);
 
-- 
2.55.0