CVE-2022-50731

In the Linux kernel, the following vulnerability has been resolved:

crypto: akcipher - default implementation for setting a private key

Changes from v1: * removed the default implementation from setpubkey: it is assumed that an implementation must always have this callback defined as there are no use case for an algorithm, which doesn't need a public key

Many akcipher implementations (like ECDSA) support only signature verifications, so they don't have all callbacks defined.

Commit 78a0324f4a53 ("crypto: akcipher - default implementations for request callbacks") introduced default callbacks for sign/verify operations, which just return an error code.

However, these are not enough, because before calling sign the caller would likely call setprivkey first on the instantiated transform (as the in-kernel testmgr does). This function does not have a default stub, so the kernel crashes, when trying to set a private key on an akcipher, which doesn't support signature generation.

I've noticed this, when trying to add a KAT vector for ECDSA signature to the testmgr.

With this patch the testmgr returns an error in dmesg (as it should) instead of crashing the kernel NULL ptr dereference.