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NFC: digital: Clear poll_tech_count before activating target

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Currently, digital_target_found() has a race between
the events started by calling nfc_targets_found()
(which ultimately expect ddev->poll_tech_count to be
zero) and setting ddev->poll_tech_count to zero after
the call to nfc_targets_found().  When the race is
"lost" (i.e., ddev->poll_tech_count is found to not
be zero by the events started by nfc_targets_found()),
an error message is printed and the target is not found.
A similar race exists when digital_tg_recv_atr_req()
calls nfc_tm_activated().

Fix this by first saving the current value of
ddev->poll_tech_count and then clearing it before
calling nfc_targets_found()/nfc_tm_activated().
Clearing ddev->poll_tech_count before calling
nfc_targets_found()/nfc_tm_activated() eliminates
the race.  Saving the value is required so it can be
restored when nfc_targets_found()/nfc_tm_activated()
fails and polling needs to continue.

Acked-by: Thierry Escande <thierry.escande@linux.intel.com>
Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
This commit is contained in:
Mark A. Greer 2014-07-02 09:03:49 -07:00 committed by Samuel Ortiz
parent 4b4dbca5e4
commit 0529a7adf3
2 changed files with 16 additions and 6 deletions
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11
net/nfc/digital_core.c
View file

@ -299,6 +299,7 @@ int digital_target_found(struct nfc_digital_dev *ddev,
int rc;
u8 framing;
u8 rf_tech;
u8 poll_tech_count;
int (*check_crc)(struct sk_buff *skb);
void (*add_crc)(struct sk_buff *skb);
@ -375,12 +376,16 @@ int digital_target_found(struct nfc_digital_dev *ddev,
return rc;
target->supported_protocols = (1 << protocol);
rc = nfc_targets_found(ddev->nfc_dev, target, 1);
if (rc)
return rc;
poll_tech_count = ddev->poll_tech_count;
ddev->poll_tech_count = 0;
rc = nfc_targets_found(ddev->nfc_dev, target, 1);
if (rc) {
ddev->poll_tech_count = poll_tech_count;
return rc;
}
return 0;
}

11
net/nfc/digital_dep.c
View file

@ -673,6 +673,7 @@ void digital_tg_recv_atr_req(struct nfc_digital_dev *ddev, void *arg,
int rc;
struct digital_atr_req *atr_req;
size_t gb_len, min_size;
u8 poll_tech_count;
if (IS_ERR(resp)) {
rc = PTR_ERR(resp);
@ -730,12 +731,16 @@ void digital_tg_recv_atr_req(struct nfc_digital_dev *ddev, void *arg,
goto exit;
gb_len = resp->len - sizeof(struct digital_atr_req);
poll_tech_count = ddev->poll_tech_count;
ddev->poll_tech_count = 0;
rc = nfc_tm_activated(ddev->nfc_dev, NFC_PROTO_NFC_DEP_MASK,
NFC_COMM_PASSIVE, atr_req->gb, gb_len);
if (rc)
if (rc) {
ddev->poll_tech_count = poll_tech_count;
goto exit;
ddev->poll_tech_count = 0;
}
rc = 0;
exit: