Re: [PATCH] crypto: public_key: check that pkey_algo is non-NULL before passing it to strcmp()

I'm intending to use Tianjia's patch.  Would you like to add a Reviewed-by?

David
---
commit 11078a592e6dcea6b9f30e822d3d30e3defc99ca
Author: Tianjia Zhang [off-list ref]
Date:   Thu Jan 7 17:28:55 2021 +0800

    X.509: Fix crash caused by NULL pointer
    
    On the following call path, `sig->pkey_algo` is not assigned
    in asymmetric_key_verify_signature(), which causes runtime
    crash in public_key_verify_signature().
    
      keyctl_pkey_verify
        asymmetric_key_verify_signature
          verify_signature
            public_key_verify_signature
    
    This patch simply check this situation and fixes the crash
    caused by NULL pointer.
    
    Fixes: 215525639631 ("X.509: support OSCCA SM2-with-SM3 certificate verification")
    Cc: stable@vger.kernel.org # v5.10+
    Reported-by: Tobias Markus [off-list ref]
    Signed-off-by: Tianjia Zhang [off-list ref]
    Signed-off-by: David Howells [off-list ref]

diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c
index 8892908ad58c..788a4ba1e2e7 100644
--- a/crypto/asymmetric_keys/public_key.c
+++ b/crypto/asymmetric_keys/public_key.c

@@ -356,7 +356,8 @@ int public_key_verify_signature(const struct public_key *pkey,
 	if (ret)
 		goto error_free_key;
 
-	if (strcmp(sig->pkey_algo, "sm2") == 0 && sig->data_size) {
+	if (sig->pkey_algo && strcmp(sig->pkey_algo, "sm2") == 0 &&
+	    sig->data_size) {
 		ret = cert_sig_digest_update(sig, tfm);
 		if (ret)
 			goto error_free_key;