tpm: tpm2_bios_measurements_next should increase position index

commit f9bf8adb upstream.

If .next function does not change position index,
following .show function will repeat output related
to current position index.

For /sys/kernel/security/tpm0/binary_bios_measurements:
1) read after lseek beyound end of file generates whole last line.
2) read after lseek to middle of last line generates
expected end of last line and unexpected whole last line once again.

Cc: stable@vger.kernel.org # 4.19.x
Fixes: 1f4aace6 ("fs/seq_file.c: simplify seq_file iteration code ...")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206283Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/tpm/eventlog/tpm2.c

@@ -143,6 +143,7 @@ static void *tpm2_bios_measurements_next(struct seq_file *m, void *v,
 	size_t event_size;
 	void *marker;
 
+	(*pos)++;
 	event_header = log->bios_event_log;
 
 	if (v == SEQ_START_TOKEN) {
@@ -167,7 +168,6 @@ static void *tpm2_bios_measurements_next(struct seq_file *m, void *v,
 	if (((v + event_size) >= limit) || (event_size == 0))
 		return NULL;
 
-	(*pos)++;
 	return v;
 }