Rework validation of chunk size.

The previous code did validate chunk size specified by userspace but did not
validate on-disk value. So if bad value were read from disk, it would cause
system crash.

I moved validation to a special function dm_snapshot_set_chunk_size. It is
called for both user's value and for value read from disk.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 drivers/md/dm-exception-store.c |    8 +++++---
 drivers/md/dm-snap.c            |   35 ++++++++++++++---------------------
 drivers/md/dm-snap.h            |    2 ++
 3 files changed, 21 insertions(+), 24 deletions(-)

Index: linux-2.6.28-rc5-devel/drivers/md/dm-snap.c
===================================================================
--- linux-2.6.28-rc5-devel.orig/drivers/md/dm-snap.c	2008-11-25 16:10:26.000000000 +0100
+++ linux-2.6.28-rc5-devel/drivers/md/dm-snap.c	2008-11-25 16:10:30.000000000 +0100
@@ -495,14 +495,20 @@ static int init_hash_tables(struct dm_sn
 	return 0;
 }
 
-/*
- * Round a number up to the nearest 'size' boundary.  size must
- * be a power of 2.
- */
-static ulong round_up(ulong n, ulong size)
+char *dm_snapshot_set_chunk_size(struct dm_snapshot *s, chunk_t chunk_size)
 {
-	size--;
-	return (n + size) & ~size;
+	if (!is_power_of_2(chunk_size)) {
+		return "Chunk size is not a power of 2";
+	}
+	if (chunk_size % (bdev_hardsect_size(s->cow->bdev) >> 9)) {
+		return "Chunk size is not a multiple of device blocksize";
+	}
+
+	s->chunk_size = chunk_size;
+	s->chunk_mask = chunk_size - 1;
+	s->chunk_shift = ffs(chunk_size) - 1;
+
+	return NULL;
 }
 
 static int set_chunk_size(struct dm_snapshot *s, const char *chunk_size_arg,
@@ -522,21 +528,8 @@ static int set_chunk_size(struct dm_snap
 		return 0;
 	}
 
-	/* Check chunk_size is a power of 2 */
-	if (!is_power_of_2(chunk_size)) {
-		*error = "Chunk size is not a power of 2";
-		return -EINVAL;
-	}
-
-	/* Validate the chunk size against the device block size */
-	if (chunk_size % (bdev_hardsect_size(s->cow->bdev) >> 9)) {
-		*error = "Chunk size is not a multiple of device blocksize";
+	if ((*error = dm_snapshot_set_chunk_size(s, chunk_size)))
 		return -EINVAL;
-	}
-
-	s->chunk_size = chunk_size;
-	s->chunk_mask = chunk_size - 1;
-	s->chunk_shift = ffs(chunk_size) - 1;
 
 	return 0;
 }
Index: linux-2.6.28-rc5-devel/drivers/md/dm-snap.h
===================================================================
--- linux-2.6.28-rc5-devel.orig/drivers/md/dm-snap.h	2008-11-25 16:10:10.000000000 +0100
+++ linux-2.6.28-rc5-devel/drivers/md/dm-snap.h	2008-11-25 16:10:30.000000000 +0100
@@ -208,6 +208,8 @@ static inline sector_t chunk_to_sector(s
 	return chunk << s->chunk_shift;
 }
 
+char *dm_snapshot_set_chunk_size(struct dm_snapshot *s, chunk_t chunk_size);
+
 static inline int bdev_equal(struct block_device *lhs, struct block_device *rhs)
 {
 	/*
Index: linux-2.6.28-rc5-devel/drivers/md/dm-exception-store.c
===================================================================
--- linux-2.6.28-rc5-devel.orig/drivers/md/dm-exception-store.c	2008-11-25 16:10:25.000000000 +0100
+++ linux-2.6.28-rc5-devel/drivers/md/dm-exception-store.c	2008-11-25 16:10:30.000000000 +0100
@@ -273,6 +273,7 @@ static int zero_disk_area(struct pstore 
 static int read_header(struct pstore *ps, int *new_snapshot)
 {
 	int r;
+	char *e;
 	struct disk_header *dh;
 	chunk_t chunk_size;
 	int chunk_size_supplied = 1;
@@ -331,9 +332,10 @@ static int read_header(struct pstore *ps
 	/* We had a bogus chunk_size. Fix stuff up. */
 	free_area(ps);
 
-	ps->snap->chunk_size = chunk_size;
-	ps->snap->chunk_mask = chunk_size - 1;
-	ps->snap->chunk_shift = ffs(chunk_size) - 1;
+	if ((e = dm_snapshot_set_chunk_size(ps->snap, chunk_size))) {
+		DMWARN("%s", e);
+		return -EINVAL;
+	}
 
 	r = dm_io_client_resize(sectors_to_pages(ps->snap->chunk_size),
 				ps->io_client);