[PATCH 1/2] sd: fix memory corruption by sd_read_cache_type

[Stefan Richter <stefanr@s5r6.in-berlin.de>]

sd: fix memory corruption by sd_read_cache_type

Let sd check more thoroughly before using mode_sense responses for data
length calculation. Fixes memory corruption ("slab error in
cache_free_debugcheck") or kernel panic when buggy disks are connected,
notably Initio SBP-2 bridges.
http://bugzilla.kernel.org/show_bug.cgi?id=6114
http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=182005

Taken from a patch by Al Viro <viro@ftp.linux.org.uk>.
http://marc.theaimsgroup.com/?l=linux-scsi&m=114055884611429

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
---
Patch is applicable to 2.6.14, 2.6.15, 2.6.16.

Index: linux-2.6.16-rc4/drivers/scsi/sd.c
===================================================================
--- linux-2.6.16-rc4.orig/drivers/scsi/sd.c	2006-02-22 22:27:42.000000000 +0100
+++ linux-2.6.16-rc4/drivers/scsi/sd.c	2006-02-22 22:29:10.000000000 +0100
@@ -1342,6 +1342,8 @@ sd_read_cache_type(struct scsi_disk *sdk
 
 	/* Take headers and block descriptors into account */
 	len += data.header_length + data.block_descriptor_length;
+	if (len > 512)
+		goto bad_sense;
 
 	/* Get the data */
 	res = sd_do_mode_sense(sdp, dbd, modepage, buffer, len, &data, &sshdr);
@@ -1354,6 +1356,12 @@ sd_read_cache_type(struct scsi_disk *sdk
 		int ct = 0;
 		int offset = data.header_length + data.block_descriptor_length;
 
+		if (offset >= 512 - 2) {
+			printk(KERN_ERR "%s: malformed MODE SENSE response",
+				diskname);
+			goto defaults;
+		}
+
 		if ((buffer[offset] & 0x3f) != modepage) {
 			printk(KERN_ERR "%s: got wrong page\n", diskname);
 			goto defaults;