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[PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data sanity check

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  [PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data sanity check Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 09:30 +0100
    Re: [PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data  sanity check Ben Hutchings <ben@decadent.org.uk> - 2017-02-24 14:40 +0100
      Re: [PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data  sanity check Johan Hovold <johan@kernel.org> - 2017-02-24 18:40 +0100
        Re: [PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data  sanity check Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-24 19:00 +0100
          Re: [PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data  sanity check Johan Hovold <johan@kernel.org> - 2017-02-24 19:20 +0100

#1587339 — [PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data sanity check

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Johan Hovold <johan@kernel.org>

commit 2d380889215fe20b8523345649dee0579821800c upstream.

Make sure to check for short transfers to avoid underflow in a loop
condition when parsing the receive buffer.

Also fix an off-by-one error in the incomplete sanity check which could
lead to invalid data being parsed.

Fixes: 8c209e6782ca ("USB: make actual_length in struct urb field u32")
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/usb/serial/digi_acceleport.c |   14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

--- a/drivers/usb/serial/digi_acceleport.c
+++ b/drivers/usb/serial/digi_acceleport.c
@@ -1483,16 +1483,20 @@ static int digi_read_oob_callback(struct
 	struct usb_serial *serial = port->serial;
 	struct tty_struct *tty;
 	struct digi_port *priv = usb_get_serial_port_data(port);
+	unsigned char *buf = urb->transfer_buffer;
 	int opcode, line, status, val;
 	int i;
 	unsigned int rts;
 
+	if (urb->actual_length < 4)
+		return -1;
+
 	/* handle each oob command */
-	for (i = 0; i < urb->actual_length - 3;) {
-		opcode = ((unsigned char *)urb->transfer_buffer)[i++];
-		line = ((unsigned char *)urb->transfer_buffer)[i++];
-		status = ((unsigned char *)urb->transfer_buffer)[i++];
-		val = ((unsigned char *)urb->transfer_buffer)[i++];
+	for (i = 0; i < urb->actual_length - 4; i += 4) {
+		opcode = buf[i];
+		line = buf[i + 1];
+		status = buf[i + 2];
+		val = buf[i + 3];
 
 		dev_dbg(&port->dev, "digi_read_oob_callback: opcode=%d, line=%d, status=%d, val=%d\n",
 			opcode, line, status, val);

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#1587673 — Re: [PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data sanity check

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On Fri, 2017-02-24 at 09:25 +0100, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Johan Hovold <johan@kernel.org>
> 
> commit 2d380889215fe20b8523345649dee0579821800c upstream.
> 
> Make sure to check for short transfers to avoid underflow in a loop
> condition when parsing the receive buffer.
> 
> Also fix an off-by-one error in the incomplete sanity check which could
> lead to invalid data being parsed.

This appears to *introduce* an off-by-one.  Which is not as serious as
the underflow, but is still a regression.

Suppose we have urb->actual_length == 4:

[...]
> -	for (i = 0; i < urb->actual_length - 3;) {

i < 1 is true, so we would run the loop once.

> -		opcode = ((unsigned char *)urb->transfer_buffer)[i++];
> -		line = ((unsigned char *)urb->transfer_buffer)[i++];
> -		status = ((unsigned char *)urb->transfer_buffer)[i++];
> -		val = ((unsigned char *)urb->transfer_buffer)[i++];
> +	for (i = 0; i < urb->actual_length - 4; i += 4) {

i < 0 is false, so we now skip the loop.

> +		opcode = buf[i];
> +		line = buf[i + 1];
> +		status = buf[i + 2];
> +		val = buf[i + 3];
[...]

Ben.

-- 
Ben Hutchings
All the simple programs have been written, and all the good names
taken.

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#1587825 — Re: [PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data sanity check

On Fri, Feb 24, 2017 at 01:38:25PM +0000, Ben Hutchings wrote: > On Fri, 2017-02-24 at 09:25 +0100, Greg Kroah-Hartman wrote:
> > 4.4-stable review patch.  If anyone has any objections, please let me know.
> > 
> > ------------------
> > 
> > From: Johan Hovold <johan@kernel.org>
> > 
> > commit 2d380889215fe20b8523345649dee0579821800c upstream.
> > 
> > Make sure to check for short transfers to avoid underflow in a loop
> > condition when parsing the receive buffer.
> > 
> > Also fix an off-by-one error in the incomplete sanity check which could
> > lead to invalid data being parsed.
> 
> This appears to *introduce* an off-by-one.  Which is not as serious as
> the underflow, but is still a regression.
> 
> Suppose we have urb->actual_length == 4:
> 
> [...]
> > -	for (i = 0; i < urb->actual_length - 3;) {
> 
> i < 1 is true, so we would run the loop once.
> 
> > -		opcode = ((unsigned char *)urb->transfer_buffer)[i++];
> > -		line = ((unsigned char *)urb->transfer_buffer)[i++];
> > -		status = ((unsigned char *)urb->transfer_buffer)[i++];
> > -		val = ((unsigned char *)urb->transfer_buffer)[i++];
> > +	for (i = 0; i < urb->actual_length - 4; i += 4) {
> 
> i < 0 is false, so we now skip the loop.

Good catch, thanks! The original loop condition was indeed correct
(modulo the missing underflow check), and I'll post a follow-up fix to
address this.

> > +		opcode = buf[i];
> > +		line = buf[i + 1];
> > +		status = buf[i + 2];
> > +		val = buf[i + 3];

You should probably not apply this one until after the follow-up is in
Linus' tree as this patch breaks TIOCMGET.

Thanks,
Johan

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#1587841 — Re: [PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data sanity check

On Fri, Feb 24, 2017 at 06:33:04PM +0100, Johan Hovold wrote:
> On Fri, Feb 24, 2017 at 01:38:25PM +0000, Ben Hutchings wrote: > On Fri, 2017-02-24 at 09:25 +0100, Greg Kroah-Hartman wrote:
> > > 4.4-stable review patch.  If anyone has any objections, please let me know.
> > > 
> > > ------------------
> > > 
> > > From: Johan Hovold <johan@kernel.org>
> > > 
> > > commit 2d380889215fe20b8523345649dee0579821800c upstream.
> > > 
> > > Make sure to check for short transfers to avoid underflow in a loop
> > > condition when parsing the receive buffer.
> > > 
> > > Also fix an off-by-one error in the incomplete sanity check which could
> > > lead to invalid data being parsed.
> > 
> > This appears to *introduce* an off-by-one.  Which is not as serious as
> > the underflow, but is still a regression.
> > 
> > Suppose we have urb->actual_length == 4:
> > 
> > [...]
> > > -	for (i = 0; i < urb->actual_length - 3;) {
> > 
> > i < 1 is true, so we would run the loop once.
> > 
> > > -		opcode = ((unsigned char *)urb->transfer_buffer)[i++];
> > > -		line = ((unsigned char *)urb->transfer_buffer)[i++];
> > > -		status = ((unsigned char *)urb->transfer_buffer)[i++];
> > > -		val = ((unsigned char *)urb->transfer_buffer)[i++];
> > > +	for (i = 0; i < urb->actual_length - 4; i += 4) {
> > 
> > i < 0 is false, so we now skip the loop.
> 
> Good catch, thanks! The original loop condition was indeed correct
> (modulo the missing underflow check), and I'll post a follow-up fix to
> address this.
> 
> > > +		opcode = buf[i];
> > > +		line = buf[i + 1];
> > > +		status = buf[i + 2];
> > > +		val = buf[i + 3];
> 
> You should probably not apply this one until after the follow-up is in
> Linus' tree as this patch breaks TIOCMGET.

Ok, I'll drop this one from the stable tree now.  Remind me to pick this
one up when the fixup hits Linus's tree.

thanks,

greg k-h

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#1587851 — Re: [PATCH 4.4 17/25] USB: serial: digi_acceleport: fix OOB data sanity check

On Fri, Feb 24, 2017 at 06:55:02PM +0100, Greg Kroah-Hartman wrote:
> On Fri, Feb 24, 2017 at 06:33:04PM +0100, Johan Hovold wrote:
> > On Fri, Feb 24, 2017 at 01:38:25PM +0000, Ben Hutchings wrote: > On Fri, 2017-02-24 at 09:25 +0100, Greg Kroah-Hartman wrote:
> > > > 4.4-stable review patch.  If anyone has any objections, please let me know.
> > > > 
> > > > ------------------
> > > > 
> > > > From: Johan Hovold <johan@kernel.org>
> > > > 
> > > > commit 2d380889215fe20b8523345649dee0579821800c upstream.
> > > > 
> > > > Make sure to check for short transfers to avoid underflow in a loop
> > > > condition when parsing the receive buffer.
> > > > 
> > > > Also fix an off-by-one error in the incomplete sanity check which could
> > > > lead to invalid data being parsed.
> > > 
> > > This appears to *introduce* an off-by-one.  Which is not as serious as
> > > the underflow, but is still a regression.

> > Good catch, thanks! The original loop condition was indeed correct
> > (modulo the missing underflow check), and I'll post a follow-up fix to
> > address this.

> > You should probably not apply this one until after the follow-up is in
> > Linus' tree as this patch breaks TIOCMGET.
> 
> Ok, I'll drop this one from the stable tree now.  Remind me to pick this
> one up when the fixup hits Linus's tree.

Thanks, will do.

Johan

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