dm: fix truncated status strings
commit fd7c092e711ebab55b2688d3859d95dfd0301f73 upstream.
Avoid returning a truncated table or status string instead of setting
the DM_BUFFER_FULL_FLAG when the last target of a table fills the
buffer.
When processing a table or status request, the function retrieve_status
calls ti->type->status. If ti->type->status returns non-zero,
retrieve_status assumes that the buffer overflowed and sets
DM_BUFFER_FULL_FLAG.
However, targets don't return non-zero values from their status method
on overflow. Most targets returns always zero.
If a buffer overflow happens in a target that is not the last in the
table, it gets noticed during the next iteration of the loop in
retrieve_status; but if a buffer overflow happens in the last target, it
goes unnoticed and erroneously truncated data is returned.
In the current code, the targets behave in the following way:
* dm-crypt returns -ENOMEM if there is not enough space to store the
key, but it returns 0 on all other overflows.
* dm-thin returns errors from the status method if a disk error happened.
This is incorrect because retrieve_status doesn't check the error
code, it assumes that all non-zero values mean buffer overflow.
* all the other targets always return 0.
This patch changes the ti->type->status function to return void (because
most targets don't use the return code). Overflow is detected in
retrieve_status: if the status method fills up the remaining space
completely, it is assumed that buffer overflow happened.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 448050c..db77ac6 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1845,8 +1845,8 @@
start_merge(s);
}
-static int snapshot_status(struct dm_target *ti, status_type_t type,
- char *result, unsigned int maxlen)
+static void snapshot_status(struct dm_target *ti, status_type_t type,
+ char *result, unsigned int maxlen)
{
unsigned sz = 0;
struct dm_snapshot *snap = ti->private;
@@ -1892,8 +1892,6 @@
maxlen - sz);
break;
}
-
- return 0;
}
static int snapshot_iterate_devices(struct dm_target *ti,
@@ -2148,8 +2146,8 @@
ti->split_io = get_origin_minimum_chunksize(dev->bdev);
}
-static int origin_status(struct dm_target *ti, status_type_t type, char *result,
- unsigned int maxlen)
+static void origin_status(struct dm_target *ti, status_type_t type, char *result,
+ unsigned int maxlen)
{
struct dm_dev *dev = ti->private;
@@ -2162,8 +2160,6 @@
snprintf(result, maxlen, "%s", dev->name);
break;
}
-
- return 0;
}
static int origin_merge(struct dm_target *ti, struct bvec_merge_data *bvm,