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Commit dfccd0f5 authored by Samuel Ortiz's avatar Samuel Ortiz
Browse files

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: default avatarSamuel Ortiz <sameo@linux.intel.com>
parent 46f793b0

drivers/nfc/pn533.c

+6 −1
Original line number Diff line number Diff line
@@ -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);

}