[OSS-Tools] [PATCH] libdt: fix of_get_devicepath looking up sibling if device unavailable

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

of_get_devicepath code flow is split into two:

  A) Either the device tree node in question has a direct udev_device
     associated with it

  B) Or we assume it's a partition and lookup udev_device for the parent
     first, before finding a child udev_device or setting a partition
     offset within the parent udev_device.

Since v2017.03.0, we have had a fallthrough from case A into case B:
If we have a udev_device, but it's neither a EEPROMs, MTDs or block
device, we just consider it a partition. This is problematic, because
this may result in us pointing at a very different device:

  - backend points at a SD-Card host. Host is enabled, but SD-Card
    is not inserted, so no block device

  - case A fails, so it's assumed it's a partition and case B
    uses parent SoC bus to lookup appropriate device

  - We fall through into the second device_find_block_device, which
    will take the first matching block device across the SoC. So
    we could end up with the eMMC: a completely different device
    than what was pointed at.

Fixes: 929ed64cb42f ("of_get_devicepath: make partition finding more robust")
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 src/libdt.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/libdt.c b/src/libdt.c
index e54d7fb5649d..7b99efe5b2de 100644
--- a/src/libdt.c
+++ b/src/libdt.c
@@ -2492,9 +2492,11 @@ int of_get_devicepath(struct device_node *partition_node, char **devpath, off_t
 		}
 
 		/*
-		 * If we found a device but couldn't classify it above, we fall
-		 * through.
+		 * If we find a udev_device but couldn't classify it above,
+		 * it's an error. Falling through would mean to handle it as a
+		 * partition and could lead us to return an arbitrary sibling device
 		 */
+		return -ENODEV;
 	}
 
 	/*
-- 
2.39.2