ldm: corrupted partition table can cause kernel oops

The kernel automatically evaluates partition tables of storage devices.
The code for evaluating LDM partitions (in fs/partitions/ldm.c) contains
a bug that causes a kernel oops on certain corrupted LDM partitions.  A
kernel subsystem seems to crash, because, after the oops, the kernel no
longer recognizes newly connected storage devices.

The patch changes ldm_parse_vmdb() to Validate the value of vblk_size.

Signed-off-by: Timo Warns <warns@pre-sense.de>
Cc: Eugene Teo <eugeneteo@kernel.sg>
Acked-by: Richard Russon <ldm@flatcap.org>
Cc: Harvey Harrison <harvey.harrison@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/partitions/ldm.c

@@ -251,6 +251,11 @@ static bool ldm_parse_vmdb (const u8 *data, struct vmdb *vm)
 	}
 
 	vm->vblk_size     = get_unaligned_be32(data + 0x08);
+	if (vm->vblk_size == 0) {
+		ldm_error ("Illegal VBLK size");
+		return false;
+	}
+
 	vm->vblk_offset   = get_unaligned_be32(data + 0x0C);
 	vm->last_vblk_seq = get_unaligned_be32(data + 0x04);