Re: [PATCH] arm64: Don't call NULL in do_compat_alignment_fixup

["Angelos Oikonomopoulos" <angelos@igalia.com>]

On Tue Apr 1, 2025 at 9:47 AM CEST, Anshuman Khandual wrote:
>
>
> On 4/1/25 12:28, Angelos Oikonomopoulos wrote:
>> On Tue Apr 1, 2025 at 8:05 AM CEST, Anshuman Khandual wrote:
>>> On 3/31/25 14:24, Angelos Oikonomopoulos wrote:
[...]
>>>>  arch/arm64/kernel/compat_alignment.c | 2 ++
>>>>  1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/arch/arm64/kernel/compat_alignment.c b/arch/arm64/kernel/compat_alignment.c
>>>> index deff21bfa680..b68e1d328d4c 100644
>>>> --- a/arch/arm64/kernel/compat_alignment.c
>>>> +++ b/arch/arm64/kernel/compat_alignment.c
>>>> @@ -368,6 +368,8 @@ int do_compat_alignment_fixup(unsigned long addr, struct pt_regs *regs)
>>>>  		return 1;
>>>>  	}
>>>>  
>>>> +	if (!handler)
>>>> +		return 1;
>>>
>>> do_alignment_t32_to_handler() could return NULL, returning 1 seems to be
>>> the right thing to do here and consistent. Otherwise does this cause a
>>> kernel crash during subsequent call into handler() ?
>> 
>> Yes. We call a NULL pointer so we Oops.
>
> Then the commit message should have the kernel Oops splash dump and also
> might need to have Fixes: and CC: stable tags etc ?

Sure, I can add those. Thanks for the suggestions!

> Also wondering if handler return value should be checked inside the switch
> block just after do_alignment_t32_to_handler() assignment.
>
> 	handler = do_alignment_t32_to_handler()
> 	if (!handler)
> 		return 1

I can see the appeal of that, but I think placing the check right before
the single dereference is a more future-proof fix, in that it reduce the
chances that a later patch will re-introduce a potential NULL pointer
dereference.

Angelos