The bug in rock.c is that it's totally trusting of the contents of the
directories.  If the directory says there's a continuation 10000 bytes into
this 4k block then we cheerily poke around in memory we don't own and oops.

So change rock_continue() to apply various sanity checks, at least ensuring
that the offset+length remain within the bounds for the header part of a
struct rock_ridge directory entry.

Note that the kernel can still overindex the buffer due to the variable size
of the rock-ridge directory entries.  We cannot check that in rock_continue()
unless we go parse the directory entry's signature and work out its size.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>