Re: [PATCH 3/3] libfdt: Check fdt_offset_ptr() return value unconditionally

[Marek Vasut <marek.vasut@mailbox.org>]

On 11/13/25 8:33 PM, Simon Glass wrote:

Hello Simon,

>> The fdt_offset_ptr() may return NULL pointer, check the return
>> value from fdt_offset_ptr() for NULL unconditionally to prevent
>> sandbox crashes.
>>
>> Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
>> ---
>> Cc: Adriano Cordova <adrianox@gmail.com>
>> Cc: Andrew Goodbody <andrew.goodbody@linaro.org>
>> Cc: Christian Marangi <ansuelsmth@gmail.com>
>> Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
>> Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
>> Cc: Patrice Chotard <patrice.chotard@foss.st.com>
>> Cc: Sam Edwards <cfsworks@gmail.com>
>> Cc: Simon Glass <sjg@chromium.org>
>> Cc: Tom Rini <trini@konsulko.com>
>> Cc: u-boot@lists.denx.de
>> ---
>>   scripts/dtc/libfdt/fdt.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/scripts/dtc/libfdt/fdt.c b/scripts/dtc/libfdt/fdt.c
>> index 95f644c31f9..d16cc3d4730 100644
>> --- a/scripts/dtc/libfdt/fdt.c
>> +++ b/scripts/dtc/libfdt/fdt.c
>> @@ -168,7 +168,7 @@ uint32_t fdt_next_tag(const void *fdt, int startoffset, int *nextoffset)
>>
>>          *nextoffset = -FDT_ERR_TRUNCATED;
>>          tagp = fdt_offset_ptr(fdt, offset, FDT_TAGSIZE);
>> -       if (!can_assume(VALID_DTB) && !tagp)
>> +       if (!tagp)
>>                  return FDT_END; /* premature end */
>>          tag = fdt32_to_cpu(*tagp);
>>          offset += FDT_TAGSIZE;
>> @@ -186,7 +186,7 @@ uint32_t fdt_next_tag(const void *fdt, int startoffset, int *nextoffset)
>>
>>          case FDT_PROP:
>>                  lenp = fdt_offset_ptr(fdt, offset, sizeof(*lenp));
>> -               if (!can_assume(VALID_DTB) && !lenp)
>> +               if (!lenp)
>>                          return FDT_END; /* premature end */
>>
>>                  len = fdt32_to_cpu(*lenp);
>> --
>> 2.51.0
>>
> 
> The can_assume() is there to be respected and helps to reduce code
> size. What problem are you actually seeing?
fdt_offset_ptr() can return NULL, and it does in test_spl on sandbox if 
I recall it right, because the U-Boot code passes in offsets which can 
not be resolved properly and that makes fdt_offset_ptr() return NULL and 
trigger SIGSEGV when it is dereferenced here.