dm: fix truncated status strings

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.

Cc: stable@vger.kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 3 insertions, 5 deletions

diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index 9e58dbd8d8cb..5a578d89da2d 100644
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -1201,8 +1201,8 @@ static int raid_map(struct dm_target *ti, struct bio *bio)
         return DM_MAPIO_SUBMITTED;
 }
 
-static int raid_status(struct dm_target *ti, status_type_t type,
-                       unsigned status_flags, char *result, unsigned maxlen)
+static void raid_status(struct dm_target *ti, status_type_t type,
+                        unsigned status_flags, char *result, unsigned maxlen)
 {
         struct raid_set *rs = ti->private;
         unsigned raid_param_cnt = 1; /* at least 1 for chunksize */
@@ -1344,8 +1344,6 @@ static int raid_status(struct dm_target *ti, status_type_t type,
                                 DMEMIT(" -");
                 }
         }
-
-        return 0;
 }
 
 static int raid_iterate_devices(struct dm_target *ti, iterate_devices_callout_fn fn, void *data)
@@ -1405,7 +1403,7 @@ static void raid_resume(struct dm_target *ti)
 
 static struct target_type raid_target = {
         .name = "raid",
-        .version = {1, 4, 1},
+        .version = {1, 4, 2},
         .module = THIS_MODULE,
         .ctr = raid_ctr,
         .dtr = raid_dtr,