Re: [PATCH v2] KEYS: prevent NULL pointer dereference in find_asymmetric_key()

Sergey Shtylyov
2024-09-10T17:38:36Z

On 9/10/24 4:38 PM, Jarkko Sakkinen wrote:
[...]

>> In find_asymmetric_key(), if all NULLs are passed in id_{0,1,2} parameters
>> the kernel will first emit WARN and then have an oops because id_2 gets
>> dereferenced anyway.
>>
>> Found by Linux Verification Center (linuxtesting.org) with Svace static
>> analysis tool.
>
> Weird, I recall that I've either sent a patch to address the same site
> OR have commented a patch with similar reasoning. Well, it does not
> matter, I think it this makes sense to me.
>
> You could further add to the motivation that given the panic_on_warn
> kernel command-line parameter, it is for the best limit the scope and
> use of the WARN-macro.

I don't understand what you mean -- this version of the patch keeps
the WARN_ON() call, it just moves that call, so that the duplicate id_{0,1,2}
checks are avoided...

>> Fixes: 7d30198ee24f ("keys: X.509 public key issuer lookup without AKID")
>
> I would still call this an improvement. It overuses warn but I don't
> think this a bug.

I think warning about passing all NULL ptrs but then causing a NULL ptr
deref anyway wasn't really intended -- seems like a bug to me...

>> Suggested-by: Sergey Shtylyov <s.shtylyov@omp.ru>
>> Signed-off-by: Roman Smirnov <r.smirnov@omp.ru>
>> Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
>> ---

I forgot to tell Roman to place the changelog here when doing an internal
review. Anyway, here is some from me:

Changed in v2:
- kept the WARN_ON() call, just moved it to avoid extra prr checks, updated
the patch description accordingly;
- reworded the patch description according to feedback.

[...]

>> diff --git a/crypto/asymmetric_keys/asymmetric_type.c b/crypto/asymmetric_keys/asymmetric_type.c
>> index a5da8ccd353e..43af5fa510c0 100644
>> --- a/crypto/asymmetric_keys/asymmetric_type.c
>> +++ b/crypto/asymmetric_keys/asymmetric_type.c
>> @@ -60,17 +60,18 @@ struct key *find_asymmetric_key(struct key *keyring,
>> char *req, *p;
>> int len;
>>
>> - WARN_ON(!id_0 && !id_1 && !id_2);
>> -
>> if (id_0) {
>> lookup = id_0->data;
>> len = id_0->len;
>> } else if (id_1) {
>> lookup = id_1->data;
>> len = id_1->len;
>> - } else {
>> + } else if (id_2) {
>> lookup = id_2->data;
>> len = id_2->len;
>> + } else {
>> + WARN_ON(1);
>
> This is totally fine. It is an improvement to the current situation.

That update also fixes a kernel oops...

>> + return ERR_PTR(-EINVAL);
>> }
>>
>> /* Construct an identifier "id:<keyid>". */
>
> Can be applied as an improvement and with the added bits about
> panic_on_warn to the commit message.

We no longer care about panic_on_warn...

> BR, Jarkko

MBR, Sergey