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

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

[Ahmad Fatoum]

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

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

[Uwe Kleine-König]

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Hello Ahmad,

On Wed, Jun 07, 2023 at 10:08:18AM +0200, Ahmad Fatoum wrote:
> 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.

So another surprise is that device_find_block_device() recurses to find
a device when starting on /soc, isn't it? Is this worth addressing?

> 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;

I don't remember the details of 929ed64cb42f any more, but probably I
didn't have a specific case that were fixed by that commit. Your
rationale makes sense.

Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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

[Ahmad Fatoum]

Hello Uwe,

On 07.06.23 10:55, Uwe Kleine-König wrote:
> Hello Ahmad,
> 
> On Wed, Jun 07, 2023 at 10:08:18AM +0200, Ahmad Fatoum wrote:
>> 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.
> 
> So another surprise is that device_find_block_device() recurses to find
> a device when starting on /soc, isn't it? Is this worth addressing?

I don't know what I'd break if I limit iteration depth and I don't know
what else I could do to curtail this..

> 
>> 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;
> 
> I don't remember the details of 929ed64cb42f any more, but probably I
> didn't have a specific case that were fixed by that commit. Your
> rationale makes sense.
> 
> Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

Thanks,
Ahmad

> 
> Best regards
> Uwe
> 

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

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

[Ahmad Fatoum]

On 07.06.23 10:08, Ahmad Fatoum wrote:
> 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>

Patch applied to next.

> ---
>  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;
>  	}
>  
>  	/*

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |