[PATCH 4.18 104/123] tpm: Return the actual size when receiving an unsupported command

[Greg Kroah-Hartman]

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ricardo Schwarzmeier <Ricardo.Schwarzmeier@xxxxxxxxxxxx>

commit 36a11029b07ee30bdc4553274d0efea645ed9d91 upstream.

The userpace expects to read the number of bytes stated in the header.
Returning the size of the buffer instead would be unexpected.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 095531f891e6 ("tpm: return a TPM_RC_COMMAND_CODE response if command is not implemented")
Signed-off-by: Ricardo Schwarzmeier <Ricardo.Schwarzmeier@xxxxxxxxxxxx>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/char/tpm/tpm-interface.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -423,7 +423,7 @@ static ssize_t tpm_try_transmit(struct t
 		header->tag = cpu_to_be16(TPM2_ST_NO_SESSIONS);
 		header->return_code = cpu_to_be32(TPM2_RC_COMMAND_CODE |
 						  TSS2_RESMGR_TPM_RC_LAYER);
-		return bufsiz;
+		return sizeof(*header);
 	}
 
 	if (bufsiz > TPM_BUFSIZE)