From 9912bbf6440ba0555e91d3306520da01872c7c1d Mon Sep 17 00:00:00 2001
From: Qu Wenruo <wqu@suse.com>
Patch-mainline: v4.19-rc1
Git-commit: 9912bbf6440ba0555e91d3306520da01872c7c1d
References: bsc#1107947
Date: Wed, 20 Jun 2018 15:38:58 +0800
Subject: [PATCH] btrfs: check-integrity: Fix NULL pointer dereference for
 degraded mount

Commit f8f84b2dfda5 ("btrfs: index check-integrity state hash by a dev_t")
changed how btrfsic indexes device state.

Now we need to access device->bdev->bd_dev, while for degraded mount
it's completely possible to have device->bdev as NULL, thus it will
trigger a NULL pointer dereference at mount time.

Fix it by checking if the device is degraded before accessing
device->bdev->bd_dev.

There are a lot of other places accessing device->bdev->bd_dev, however
the other call sites have either checked device->bdev, or the
device->bdev is passed from btrfsic_map_block(), so it won't cause harm.

Fixes: f8f84b2dfda5 ("btrfs: index check-integrity state hash by a dev_t")
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/check-integrity.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/fs/btrfs/check-integrity.c
+++ b/fs/btrfs/check-integrity.c
@@ -1552,7 +1552,11 @@ static int btrfsic_map_block(struct btrf
 	}
 
 	device = multi->stripes[0].dev;
-	block_ctx_out->dev = btrfsic_dev_state_lookup(device->bdev->bd_dev);
+	if (device->missing || !device->bdev || !device->name)
+		block_ctx_out->dev = NULL;
+	else
+		block_ctx_out->dev = btrfsic_dev_state_lookup(
+							device->bdev->bd_dev);
 	block_ctx_out->dev_bytenr = multi->stripes[0].physical;
 	block_ctx_out->start = bytenr;
 	block_ctx_out->len = len;