Re: [PATCH 3/3] nfc: trf7970a: Prevent repeated polling from crashing the kernel

[Mark Greer]

On Tue, Dec 20, 2016 at 11:16:32AM -0500, Geoff Lansberry wrote:
> From: Jaret Cantu 
> 
> Repeated polling attempts cause a NULL dereference error to occur.
> This is because the state of the trf7970a is currently reading but
> another request has been made to send a command before it has finished.

How is this happening?  Was trf7970a_abort_cmd() called and it didn't
work right?  Was it not called at all and there is a bug in the digital
layer?  More details please.

> The solution is to properly kill the waiting reading (workqueue)
> before failing on the send.

If the bug is in the calling code, then that is what should get fixed.
This seems to be a hack to work-around a digital layer bug.

Mark
--

[PATCH 3/3] nfc: trf7970a: Prevent repeated polling from crashing the kernel

[Geoff Lansberry]

From: Jaret Cantu 

Repeated polling attempts cause a NULL dereference error to occur.
This is because the state of the trf7970a is currently reading but
another request has been made to send a command before it has finished.

The solution is to properly kill the waiting reading (workqueue)
before failing on the send.
---
 drivers/nfc/trf7970a.c | 4 
 1 file changed, 4 insertions(+)

diff --git a/drivers/nfc/trf7970a.c b/drivers/nfc/trf7970a.c
index 8a88195..5916737 100644
--- a/drivers/nfc/trf7970a.c
+++ b/drivers/nfc/trf7970a.c
@@ -1496,6 +1496,10 @@ static int trf7970a_send_cmd(struct nfc_digital_dev 
*ddev,
(trf->state != TRF7970A_ST_IDLE_RX_BLOCKED)) {
dev_err(trf->dev, "%s - Bogus state: %d\n", __func__,
trf->state);
+   if (trf->state == TRF7970A_ST_WAIT_FOR_RX_DATA ||
+   trf->state == TRF7970A_ST_WAIT_FOR_RX_DATA_CONT)
+   trf->ignore_timeout =
+   !cancel_delayed_work(>timeout_work);
ret = -EIO;
goto out_err;
}
-- 
Signed-off-by: Geoff Lansberry 

[PATCH 3/3] nfc: trf7970a: Prevent repeated polling from crashing the kernel

[Geoff Lansberry]

From: Jaret Cantu 

Repeated polling attempts cause a NULL dereference error to occur.
This is because the state of the trf7970a is currently reading but
another request has been made to send a command before it has finished.

The solution is to properly kill the waiting reading (workqueue)
before failing on the send.
---
 drivers/nfc/trf7970a.c | 4 
 1 file changed, 4 insertions(+)

diff --git a/drivers/nfc/trf7970a.c b/drivers/nfc/trf7970a.c
index 8a88195..5916737 100644
--- a/drivers/nfc/trf7970a.c
+++ b/drivers/nfc/trf7970a.c
@@ -1496,6 +1496,10 @@ static int trf7970a_send_cmd(struct nfc_digital_dev 
*ddev,
(trf->state != TRF7970A_ST_IDLE_RX_BLOCKED)) {
dev_err(trf->dev, "%s - Bogus state: %d\n", __func__,
trf->state);
+   if (trf->state == TRF7970A_ST_WAIT_FOR_RX_DATA ||
+   trf->state == TRF7970A_ST_WAIT_FOR_RX_DATA_CONT)
+   trf->ignore_timeout =
+   !cancel_delayed_work(>timeout_work);
ret = -EIO;
goto out_err;
}
-- 
Signed-off-by: Geoff Lansberry 

Re: [PATCH 3/3] nfc: trf7970a: Prevent repeated polling from crashing the kernel

[Mark Greer]

On Thu, Dec 15, 2016 at 05:30:44PM -0500, Geoff Lansberry wrote:
> From: Jaret Cantu 
> 
> Repeated polling attempts cause a NULL dereference error to occur.
> This is because the curent state of the trf7970a is reading but
> a request has been made to send a command.
> 
> The solution is to properly kill the waiting reading (workqueue)
> before failing on the send.

Maybe its just me but I find this description a little hard to grok.
Mind reworking it?

The patch itself looks fine.

Thanks,

Mark
--

[PATCH 3/3] nfc: trf7970a: Prevent repeated polling from crashing the kernel

[Geoff Lansberry]

From: Jaret Cantu 

Repeated polling attempts cause a NULL dereference error to occur.
This is because the curent state of the trf7970a is reading but
a request has been made to send a command.

The solution is to properly kill the waiting reading (workqueue)
before failing on the send.
---
 drivers/nfc/trf7970a.c | 4 
 1 file changed, 4 insertions(+)

diff --git a/drivers/nfc/trf7970a.c b/drivers/nfc/trf7970a.c
index b4c37ab..f96a321 100644
--- a/drivers/nfc/trf7970a.c
+++ b/drivers/nfc/trf7970a.c
@@ -1493,6 +1493,10 @@ static int trf7970a_send_cmd(struct nfc_digital_dev 
*ddev,
(trf->state != TRF7970A_ST_IDLE_RX_BLOCKED)) {
dev_err(trf->dev, "%s - Bogus state: %d\n", __func__,
trf->state);
+   if (trf->state == TRF7970A_ST_WAIT_FOR_RX_DATA ||
+   trf->state == TRF7970A_ST_WAIT_FOR_RX_DATA_CONT)
+   trf->ignore_timeout =
+   !cancel_delayed_work(>timeout_work);
ret = -EIO;
goto out_err;
}
-- 
Signed-off-by: Geoff Lansberry