[PATCH] sd: fix memory corruption with broken mode page headers

sd: fix memory corruption with broken mode page headers

There's a problem in sd where we blindly believe the length of the
headers and block descriptors.  Some devices return insane values for
these and cause our length to end up greater than the actual buffer
size, so check to make sure.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Also removed the buffer size magic number (512) and added DPOFUA of
zero to the defaults

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

rediff for 2.6.15.x without DPOFUA bit, taken from commit
48970800

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>