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

When public_key_verify_signature() is called from
asymmetric_key_verify_signature(), the pkey_algo field of struct
public_key_signature will be NULL, which causes a NULL pointer dereference
in the strcmp() check. Fix this by adding a NULL check.

One visible manifestation of this is that userspace programs (such as the
'iwd' WiFi daemon) will be killed when trying to verify a TLS key using the
keyctl(2) interface.

Cc: stable@vger.kernel.org
Fixes: 215525639631 ("X.509: support OSCCA SM2-with-SM3 certificate verification")
Signed-off-by: Toke Høiland-Jørgensen <redacted>
---
 crypto/asymmetric_keys/public_key.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c
index 8892908ad58c..35b09e95a870 100644
--- a/crypto/asymmetric_keys/public_key.c
+++ b/crypto/asymmetric_keys/public_key.c

@@ -356,7 +356,7 @@ 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;

-- 
2.30.0