[PATCH] X.509: Fix validation of ASN.1 certificate header

x509_load_certificate_list() seeks to enforce that a certificate starts
with 0x30 0x82 (ASN.1 SEQUENCE tag followed by a length of more than 256
and less than 65535 bytes).

But it only enforces that *either* of those two byte values are present,
instead of checking for the *conjunction* of the two values.  Fix it.

Fixes: 631cc66eb9ea ("MODSIGN: Provide module signing public keys to the kernel")
Reported-by: Sashiko <[email protected]>
Closes: https://lore.kernel.org/r/[email protected]/
Signed-off-by: Lukas Wunner <[email protected]>
Cc: [email protected] # v3.7+
---
 crypto/asymmetric_keys/x509_loader.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crypto/asymmetric_keys/x509_loader.c b/crypto/asymmetric_keys/x509_loader.c
index a417413..0d516c7 100644
--- a/crypto/asymmetric_keys/x509_loader.c
+++ b/crypto/asymmetric_keys/x509_loader.c
@@ -20,7 +20,7 @@ int x509_load_certificate_list(const u8 cert_list[],
 		 */
 		if (end - p < 4)
 			goto dodgy_cert;
-		if (p[0] != 0x30 &&
+		if (p[0] != 0x30 ||
 		    p[1] != 0x82)
 			goto dodgy_cert;
 		plen = (p[2] << 8) | p[3];
-- 
2.51.0