[PATCH v3] mkimage: Default to 8-byte alignment for DTBs added via -b argument

[Sean Anderson]

On 1/27/26 13:52, Marek Vasut wrote:
> On 1/27/26 5:38 PM, Tom Rini wrote:
>
>>> No, the check in fdt_getprop is only for the name, not the value (which
>>> could be arbitrary binary data including many nul bytes).
>>>
>>> I think the assumption in most of U-Boot is that the provided FDT is
>>> trusted (or at least not maliciously ill-formed).  functions like
>>> image_get_checksum_algo read up to 6 bytes beyond full_name if full_name
>>> == "". It's possible to read off the end of the DTB if this is the very
>>> last string in the strings block and there is no trailing padding. If
>>> we're really concerned about this (e.g. to avoid false-positives with
>>> ASAN), then we should just add (say) 16 bytes to the end of every DTB
>>> when we malloc it.
>>
>> Yes, we rely on the sanity checking in libfdt, which I think the kernel
>> also does.
>>
>> And no, I'm not sure if we care enough about all of these corner cases,
>> but if we do then I'm not sure this right here and now is where to
>> start. It should start with upstream libfdt to see whatever cases aren't
>> handled, and then what cases fall on the callers to deal with wrt
>> security implications.
>>
>> Because I really, really, really, do not want to block fixing booting on
>> some large number of boards because now we're going to depend first on a
>> security audit here.
> So back to my and Sean suggestion:
>
> fdt_string_eq_() does effectively memcmp():
>
> return p && (slen == len) && (memcmp(p, s, len) == 0);
>
> So do this and be done with it ?
>
> type = fdt_getprop(fdt, node, FIT_TYPE_PROP, &len);
> if (type && len == strlen(FIT_TYPE_PROP) && !memcmp(type, "flat_dt", len))

this is wrong it needs to be

type && len == sizeof("flat_dt") && !memcmp(type, "flat_dt", len)

and it's exactly the sort of error I was complaining about earlier :)

--Sean

>   align_size = 8;


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