[lvc-project] [PATCH v2] nfc: pn533: Add poll mod list filling check

[Aleksandr Mishin]

In case of im_protocols value is 1 and tm_protocols value is 0 this
combination successfully passes the check
'if (!im_protocols && !tm_protocols)' in the nfc_start_poll().
But then after pn533_poll_create_mod_list() call in pn533_start_poll()
poll mod list will remain empty and dev->poll_mod_count will remain 0
which lead to division by zero.

Normally no im protocol has value 1 in the mask, so this combination is
not expected by driver. But these protocol values actually come from
userspace via Netlink interface (NFC_CMD_START_POLL operation). So a
broken or malicious program may pass a message containing a "bad"
combination of protocol parameter values so that dev->poll_mod_count
is not incremented inside pn533_poll_create_mod_list(), thus leading
to division by zero.
Call trace looks like:
nfc_genl_start_poll()
  nfc_start_poll()
    ->start_poll()
    pn533_start_poll()

Add poll mod list filling check.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: dfccd0f58044 ("NFC: pn533: Add some polling entropy")
Signed-off-by: Aleksandr Mishin <amishin at t-argos.ru>
---
v2: Update comment message for a more detailed description of the problem

 drivers/nfc/pn533/pn533.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/nfc/pn533/pn533.c b/drivers/nfc/pn533/pn533.c
index b19c39dcfbd9..e2bc67300a91 100644
--- a/drivers/nfc/pn533/pn533.c
+++ b/drivers/nfc/pn533/pn533.c
@@ -1723,6 +1723,11 @@ static int pn533_start_poll(struct nfc_dev *nfc_dev,
 	}
 
 	pn533_poll_create_mod_list(dev, im_protocols, tm_protocols);
+	if (!dev->poll_mod_count) {
+		nfc_err(dev->dev,
+			"Poll mod list is empty\n");
+		return -EINVAL;
+	}
 
 	/* Do not always start polling from the same modulation */
 	get_random_bytes(&rand_mod, sizeof(rand_mod));
-- 
2.30.2