Commit c6606290 authored by Marko Kohtala's avatar Marko Kohtala Committed by Linus Torvalds
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[PATCH] parport: buffer overflow fix 



Fix potential buffer overflow in case the device ID did not end in semicolon.
Also might fail to negotiate back to IEEE1284_MODE_COMPAT in case of failure.
parport_device_id did not return what Documentation/parport-lowlevel.txt said,
so I changed it to match it.

Determining device ID length is overly complicated, but Tim Waugh recalled on
linux-parport seeing some buggy device that might need it.

Signed-off-by: default avatarMarko Kohtala <marko.kohtala@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 39ee059a

drivers/parport/probe.c

+130 −63
Original line number Diff line number Diff line
@@ -128,8 +128,131 @@ static void parse_data(struct parport *port, int device, char *str) 
	kfree(txt);

}



/* Read up to count-1 bytes of device id. Terminate buffer with

 * '\0'. Buffer begins with two Device ID length bytes as given by

 * device. */

static ssize_t parport_read_device_id (struct parport *port, char *buffer,

				       size_t count)

{

	unsigned char length[2];

	unsigned lelen, belen;

	size_t idlens[4];

	unsigned numidlens;

	unsigned current_idlen;

	ssize_t retval;

	size_t len;



	/* First two bytes are MSB,LSB of inclusive length. */

	retval = parport_read (port, length, 2);



	if (retval < 0)

		return retval;

	if (retval != 2)

		return -EIO;



	if (count < 2)

		return 0;

	memcpy(buffer, length, 2);

	len = 2;



	/* Some devices wrongly send LE length, and some send it two

	 * bytes short. Construct a sorted array of lengths to try. */

	belen = (length[0] << 8) + length[1];

	lelen = (length[1] << 8) + length[0];

	idlens[0] = min(belen, lelen);

	idlens[1] = idlens[0]+2;

	if (belen != lelen) {

		int off = 2;

		/* Don't try lenghts of 0x100 and 0x200 as 1 and 2 */

		if (idlens[0] <= 2)

			off = 0;

		idlens[off] = max(belen, lelen);

		idlens[off+1] = idlens[off]+2;

		numidlens = off+2;

	}

	else {

		/* Some devices don't truly implement Device ID, but

		 * just return constant nibble forever. This catches

		 * also those cases. */

		if (idlens[0] == 0 || idlens[0] > 0xFFF) {

			printk (KERN_DEBUG "%s: reported broken Device ID"

				" length of %#zX bytes\n",

				port->name, idlens[0]);

			return -EIO;

		}

		numidlens = 2;

	}



	/* Try to respect the given ID length despite all the bugs in

	 * the ID length. Read according to shortest possible ID

	 * first. */

	for (current_idlen = 0; current_idlen < numidlens; ++current_idlen) {

		size_t idlen = idlens[current_idlen];

		if (idlen+1 >= count)

			break;



		retval = parport_read (port, buffer+len, idlen-len);



		if (retval < 0)

			return retval;

		len += retval;



		if (port->physport->ieee1284.phase != IEEE1284_PH_HBUSY_DAVAIL) {

			if (belen != len) {

				printk (KERN_DEBUG "%s: Device ID was %d bytes"

					" while device told it would be %d"

					" bytes\n",

					port->name, len, belen);

			}

			goto done;

		}



		/* This might end reading the Device ID too

		 * soon. Hopefully the needed fields were already in

		 * the first 256 bytes or so that we must have read so

		 * far. */

		if (buffer[len-1] == ';') {

 			printk (KERN_DEBUG "%s: Device ID reading stopped"

				" before device told data not available. "

				"Current idlen %d of %d, len bytes %02X %02X\n",

				port->name, current_idlen, numidlens,

				length[0], length[1]);

			goto done;

		}

	}

	if (current_idlen < numidlens) {

		/* Buffer not large enough, read to end of buffer. */

		size_t idlen, len2;

		if (len+1 < count) {

			retval = parport_read (port, buffer+len, count-len-1);

			if (retval < 0)

				return retval;

			len += retval;

		}

		/* Read the whole ID since some devices would not

		 * otherwise give back the Device ID from beginning

		 * next time when asked. */

		idlen = idlens[current_idlen];

		len2 = len;

		while(len2 < idlen && retval > 0) {

			char tmp[4];

			retval = parport_read (port, tmp,

					       min(sizeof tmp, idlen-len2));

			if (retval < 0)

				return retval;

			len2 += retval;

		}

	}

	/* In addition, there are broken devices out there that don't

	   even finish off with a semi-colon. We do not need to care

	   about those at this time. */

 done:

	buffer[len] = '\0';

	return len;

}



/* Get Std 1284 Device ID. */

ssize_t parport_device_id (int devnum, char *buffer, size_t len)

ssize_t parport_device_id (int devnum, char *buffer, size_t count)

{

	ssize_t retval = -ENXIO;

	struct pardevice *dev = parport_open (devnum, "Device ID probe",
@@ -139,76 +262,20 @@ ssize_t parport_device_id (int devnum, char *buffer, size_t len) 


	parport_claim_or_block (dev);



	/* Negotiate to compatibility mode, and then to device ID mode.

	 * (This is in case we are already in device ID mode.) */

	/* Negotiate to compatibility mode, and then to device ID

	 * mode. (This so that we start form beginning of device ID if

	 * already in device ID mode.) */

	parport_negotiate (dev->port, IEEE1284_MODE_COMPAT);

	retval = parport_negotiate (dev->port,

				    IEEE1284_MODE_NIBBLE | IEEE1284_DEVICEID);



	if (!retval) {

		int idlen;

		unsigned char length[2];



		/* First two bytes are MSB,LSB of inclusive length. */

		retval = parport_read (dev->port, length, 2);



		if (retval != 2) goto end_id;



		idlen = (length[0] << 8) + length[1] - 2;

		/*

		 * Check if the caller-allocated buffer is large enough

		 * otherwise bail out or there will be an at least off by one.

		 */

		if (idlen + 1 < len)

			len = idlen;

		else {

			retval = -EINVAL;

			goto out;

		}

		retval = parport_read (dev->port, buffer, len);



		if (retval != len)

			printk (KERN_DEBUG "%s: only read %Zd of %Zd ID bytes\n",

				dev->port->name, retval,

				len);



		/* Some printer manufacturers mistakenly believe that

                   the length field is supposed to be _exclusive_.

		   In addition, there are broken devices out there

                   that don't even finish off with a semi-colon. */

		if (buffer[len - 1] != ';') {

			ssize_t diff;

			diff = parport_read (dev->port, buffer + len, 2);

			retval += diff;



			if (diff)

				printk (KERN_DEBUG

					"%s: device reported incorrect "

					"length field (%d, should be %Zd)\n",

					dev->port->name, idlen, retval);

			else {

				/* One semi-colon short of a device ID. */

				buffer[len++] = ';';

				printk (KERN_DEBUG "%s: faking semi-colon\n",

					dev->port->name);



				/* If we get here, I don't think we

                                   need to worry about the possible

                                   standard violation of having read

                                   more than we were told to.  The

                                   device is non-compliant anyhow. */

			}

		}



	end_id:

		buffer[len] = '\0';

		retval = parport_read_device_id (dev->port, buffer, count);

		parport_negotiate (dev->port, IEEE1284_MODE_COMPAT);

	}



		if (retval > 2)

		parse_data (dev->port, dev->daisy, buffer);

			parse_data (dev->port, dev->daisy, buffer+2);

	}



out:

	parport_release (dev);

	parport_close (dev);

	return retval;

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