[PATCH] Subject: cdrom.c get_last_written fixup

There's something wrong in cdrom.c: cdrom_get_last_written() for instance
calls cdrom_get_disc_info() and cdrom_get_track_info() to get information
about tracks, but these functions don't ensure that all the
track_information or disc_information structure is filled:

	/* (buflen was first set to 8 to get track_information_length field) */

	if ((ret = cdo->generic_packet(cdi, &cgc)))
		return ret;

	cgc.buflen = be16_to_cpu(ti->track_information_length) +
		     sizeof(ti->track_information_length);

	if (cgc.buflen > sizeof(track_information))
		cgc.buflen = sizeof(track_information);

	cgc.cmd[8] = cgc.buflen;
	return cdo->generic_packet(cdi, &cgc);

The second test ensures that at least we won't overflow the structure, but
nothing ensures that all the structure will be filled.

And indeed, we have a drive here that won't fill it all: the returned
track_information_length field will be *less than*
sizeof(track_information) - sizeof(ti->track_information_length), so that
cdrom_get_last_written() reads values that weren't filled in!  As a result,
we are sometimes unable to read some parts of CDROMs, depending on the
uninitialized state of the structure...

Here is a patch that adds filling checks: cdrom_get_disc_info() and
cdrom_get_track_info() return the actual filled length, and it's up to the
caller to check that this is enough for him to get the values it wants.

Note: adding something like a
#define spanof(TYPE, MEMBER) ((size_t) ((&((TYPE *)0)->MEMBER)+1))
definition just near that of offsetof() in include/linux/stddef.h would
make it more pretty, but still it won't help for bitfields :/
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/cdrom/cdrom.c

@@ -607,7 +607,7 @@ static int cdrom_mrw_exit(struct cdrom_device_info *cdi)
 	disc_information di;
 	int ret = 0;
 
-	if (cdrom_get_disc_info(cdi, &di))
+	if (cdrom_get_disc_info(cdi, &di) < offsetof(typeof(di),disc_type))
 		return 1;
 
 	if (di.mrw_status == CDM_MRW_BGFORMAT_ACTIVE) {
@@ -716,7 +716,7 @@ static int cdrom_media_erasable(struct cdrom_device_info *cdi)
 {
 	disc_information di;
 
-	if (cdrom_get_disc_info(cdi, &di))
+	if (cdrom_get_disc_info(cdi, &di) < offsetof(typeof(di),n_first_track))
 		return -1;
 
 	return di.erasable;
@@ -752,7 +752,7 @@ static int cdrom_mrw_open_write(struct cdrom_device_info *cdi)
 		return 1;
 	}
 
-	if (cdrom_get_disc_info(cdi, &di))
+	if (cdrom_get_disc_info(cdi, &di) < offsetof(typeof(di),disc_type))
 		return 1;
 
 	if (!di.erasable)
@@ -2760,7 +2760,7 @@ static int cdrom_get_track_info(struct cdrom_device_info *cdi, __u16 track, __u8
 {
 	struct cdrom_device_ops *cdo = cdi->ops;
 	struct packet_command cgc;
-	int ret;
+	int ret, buflen;
 
 	init_cdrom_command(&cgc, ti, 8, CGC_DATA_READ);
 	cgc.cmd[0] = GPCMD_READ_TRACK_RZONE_INFO;
@@ -2773,14 +2773,18 @@ static int cdrom_get_track_info(struct cdrom_device_info *cdi, __u16 track, __u8
 	if ((ret = cdo->generic_packet(cdi, &cgc)))
 		return ret;
 	
-	cgc.buflen = be16_to_cpu(ti->track_information_length) +
+	buflen = be16_to_cpu(ti->track_information_length) +
 		     sizeof(ti->track_information_length);
 
-	if (cgc.buflen > sizeof(track_information))
-		cgc.buflen = sizeof(track_information);
+	if (buflen > sizeof(track_information))
+		buflen = sizeof(track_information);
 
-	cgc.cmd[8] = cgc.buflen;
-	return cdo->generic_packet(cdi, &cgc);
+	cgc.cmd[8] = cgc.buflen = buflen;
+	if ((ret = cdo->generic_packet(cdi, &cgc)))
+		return ret;
+
+	/* return actual fill size */
+	return buflen;
 }
 
 /* requires CD R/RW */
@@ -2788,7 +2792,7 @@ static int cdrom_get_disc_info(struct cdrom_device_info *cdi, disc_information *
 {
 	struct cdrom_device_ops *cdo = cdi->ops;
 	struct packet_command cgc;
-	int ret;
+	int ret, buflen;
 
 	/* set up command and get the disc info */
 	init_cdrom_command(&cgc, di, sizeof(*di), CGC_DATA_READ);
@@ -2802,14 +2806,18 @@ static int cdrom_get_disc_info(struct cdrom_device_info *cdi, disc_information *
 	/* not all drives have the same disc_info length, so requeue
 	 * packet with the length the drive tells us it can supply
 	 */
-	cgc.buflen = be16_to_cpu(di->disc_information_length) +
+	buflen = be16_to_cpu(di->disc_information_length) +
 		     sizeof(di->disc_information_length);
 
-	if (cgc.buflen > sizeof(disc_information))
-		cgc.buflen = sizeof(disc_information);
+	if (buflen > sizeof(disc_information))
+		buflen = sizeof(disc_information);
 
-	cgc.cmd[8] = cgc.buflen;
-	return cdo->generic_packet(cdi, &cgc);
+	cgc.cmd[8] = cgc.buflen = buflen;
+	if ((ret = cdo->generic_packet(cdi, &cgc)))
+		return ret;
+
+	/* return actual fill size */
+	return buflen;
 }
 
 /* return the last written block on the CD-R media. this is for the udf
@@ -2820,27 +2828,33 @@ int cdrom_get_last_written(struct cdrom_device_info *cdi, long *last_written)
 	disc_information di;
 	track_information ti;
 	__u32 last_track;
-	int ret = -1;
+	int ret = -1, ti_size;
 
 	if (!CDROM_CAN(CDC_GENERIC_PACKET))
 		goto use_toc;
 
-	if ((ret = cdrom_get_disc_info(cdi, &di)))
+	if ((ret = cdrom_get_disc_info(cdi, &di))
+			< offsetof(typeof(di), last_track_msb)
+			+ sizeof(di.last_track_msb))
 		goto use_toc;
 
 	last_track = (di.last_track_msb << 8) | di.last_track_lsb;
-	if ((ret = cdrom_get_track_info(cdi, last_track, 1, &ti)))
+	ti_size = cdrom_get_track_info(cdi, last_track, 1, &ti);
+	if (ti_size < offsetof(typeof(ti), track_start))
 		goto use_toc;
 
 	/* if this track is blank, try the previous. */
 	if (ti.blank) {
 		last_track--;
-		if ((ret = cdrom_get_track_info(cdi, last_track, 1, &ti)))
-			goto use_toc;
+		ti_size = cdrom_get_track_info(cdi, last_track, 1, &ti);
 	}
 
+	if (ti_size < offsetof(typeof(ti), track_size) + sizeof(ti.track_size))
+		goto use_toc;
+
 	/* if last recorded field is valid, return it. */
-	if (ti.lra_v) {
+	if (ti.lra_v && ti_size >= offsetof(typeof(ti), last_rec_address)
+				+ sizeof(ti.last_rec_address)) {
 		*last_written = be32_to_cpu(ti.last_rec_address);
 	} else {
 		/* make it up instead */
@@ -2853,11 +2867,12 @@ int cdrom_get_last_written(struct cdrom_device_info *cdi, long *last_written)
 
 	/* this is where we end up if the drive either can't do a
 	   GPCMD_READ_DISC_INFO or GPCMD_READ_TRACK_RZONE_INFO or if
-	   it fails. then we return the toc contents. */
+	   it doesn't give enough information or fails. then we return
+	   the toc contents. */
 use_toc:
 	toc.cdte_format = CDROM_MSF;
 	toc.cdte_track = CDROM_LEADOUT;
-	if (cdi->ops->audio_ioctl(cdi, CDROMREADTOCENTRY, &toc))
+	if ((ret = cdi->ops->audio_ioctl(cdi, CDROMREADTOCENTRY, &toc)))
 		return ret;
 	sanitize_format(&toc.cdte_addr, &toc.cdte_format, CDROM_LBA);
 	*last_written = toc.cdte_addr.lba;
@@ -2870,32 +2885,33 @@ static int cdrom_get_next_writable(struct cdrom_device_info *cdi, long *next_wri
 	disc_information di;
 	track_information ti;
 	__u16 last_track;
-	int ret = -1;
+	int ret = -1, ti_size;
 
 	if (!CDROM_CAN(CDC_GENERIC_PACKET))
 		goto use_last_written;
 
-	if ((ret = cdrom_get_disc_info(cdi, &di)))
+	if ((ret = cdrom_get_disc_info(cdi, &di))
+			< offsetof(typeof(di), last_track_msb)
+			+ sizeof(di.last_track_msb))
 		goto use_last_written;
 
 	last_track = (di.last_track_msb << 8) | di.last_track_lsb;
-	if ((ret = cdrom_get_track_info(cdi, last_track, 1, &ti)))
+	ti_size = cdrom_get_track_info(cdi, last_track, 1, &ti);
+	if (ti_size < offsetof(typeof(ti), track_start))
 		goto use_last_written;
 
         /* if this track is blank, try the previous. */
 	if (ti.blank) {
 		last_track--;
-		if ((ret = cdrom_get_track_info(cdi, last_track, 1, &ti)))
-			goto use_last_written;
+		ti_size = cdrom_get_track_info(cdi, last_track, 1, &ti);
 	}
 
 	/* if next recordable address field is valid, use it. */
-	if (ti.nwa_v)
+	if (ti.nwa_v && ti_size >= offsetof(typeof(ti), next_writable)
+				+ sizeof(ti.next_writable)) {
 		*next_writable = be32_to_cpu(ti.next_writable);
-	else
-		goto use_last_written;
-
-	return 0;
+		return 0;
+	}
 
 use_last_written:
 	if ((ret = cdrom_get_last_written(cdi, next_writable))) {