From dfccd0f580445d176acea174175b3e6518cc91f7 Mon Sep 17 00:00:00 2001 From: Samuel Ortiz Date: Wed, 3 Jul 2013 15:14:17 +0200 Subject: [PATCH] NFC: pn533: Add some polling entropy By not always starting the polling loop from the same modulation, we avoid entering infinite loops where devices exporting 2 targets (on 2 different modulations) get the same target activated over and over. If this target is not readable (e.g. a wallet emulating a tag), we will stay in an error loop for ever. Signed-off-by: Samuel Ortiz --- drivers/nfc/pn533.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/nfc/pn533.c b/drivers/nfc/pn533.c index 9f3868b0170b..5df730be88a3 100644 --- a/drivers/nfc/pn533.c +++ b/drivers/nfc/pn533.c @@ -1913,6 +1913,7 @@ static int pn533_start_poll(struct nfc_dev *nfc_dev, u32 im_protocols, u32 tm_protocols) { struct pn533 *dev = nfc_get_drvdata(nfc_dev); + u8 rand_mod; nfc_dev_dbg(&dev->interface->dev, "%s: im protocols 0x%x tm protocols 0x%x", @@ -1936,11 +1937,15 @@ static int pn533_start_poll(struct nfc_dev *nfc_dev, tm_protocols = 0; } - dev->poll_mod_curr = 0; pn533_poll_create_mod_list(dev, im_protocols, tm_protocols); dev->poll_protocols = im_protocols; dev->listen_protocols = tm_protocols; + /* Do not always start polling from the same modulation */ + get_random_bytes(&rand_mod, sizeof(rand_mod)); + rand_mod %= dev->poll_mod_count; + dev->poll_mod_curr = rand_mod; + return pn533_send_poll_frame(dev); }