[Devel] [PATCH hci-8.1] dm: don't inherit bio-based table type for targets without ->map

[Alexander Ivanov <alexander.ivanov@virtuozzo.com>]

A table whose single target has no devices inherits the live table's
type in dm_table_determine_type(). dm-qcow2 and dm-ploop open their
images by fd and never call dm_get_device(), so loading them over a
bio-based live table makes the table bio-based although these targets
have no ->map. The first bio then calls a NULL ->map from __map_bio():

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  RIP: 0010:0x0
   __map_bio+0x197/0x1c0 [dm_mod]
   dm_split_and_process_bio+0x1ad/0x740 [dm_mod]

Inherit the live table's type only if the target has ->map, so it can
run bio-based. Otherwise keep the request-based type, so table_load()
rejects the mismatch with "can't change device type".

https://virtuozzo.atlassian.net/browse/VSTOR-150573
Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
---
 drivers/md/dm-table.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 954bbc338bce..a12b1cbe4336 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -987,8 +987,8 @@ static int dm_table_determine_type(struct dm_table *t)
 		int srcu_idx;
 		struct dm_table *live_table = dm_get_live_table(t->md, &srcu_idx);
 
-		/* inherit live table's type */
-		if (live_table)
+		/* only a bio-capable target inherits live table's type */
+		if (live_table && dm_target_bio_based(dm_table_get_target(t, 0)))
 			t->type = live_table->type;
 		dm_put_live_table(t->md, srcu_idx);
 		return 0;
-- 
2.53.0

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