linux-kernel - Re: [PATCH v2 5/7] efi: Import certificates from UEFI Secure Boot

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Date:   Wed, 12 Dec 2018 23:01:15 +0530
From:   Nayna Jain <nayna@...ux.ibm.com>
To:     James Morris <jmorris@...ei.org>
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, zohar@...ux.ibm.com,
        dhowells@...hat.com, jforbes@...hat.com,
        seth.forshee@...onical.com, kexec@...ts.infradead.org,
        keyrings@...r.kernel.org, vgoyal@...hat.com, ebiederm@...ssion.com,
        mpe@...erman.id.au, Josh Boyer <jwboyer@...oraproject.org>
Subject: Re: [PATCH v2 5/7] efi: Import certificates from UEFI Secure Boot



On 12/12/2018 12:17 AM, James Morris wrote:
> On Sun, 9 Dec 2018, Nayna Jain wrote:
>
>> +/*
>> + * Blacklist an X509 TBS hash.
>> + */
>> +static __init void uefi_blacklist_x509_tbs(const char *source,
>> +					   const void *data, size_t len)
>> +{
>> +	char *hash, *p;
>> +
>> +	hash = kmalloc(4 + len * 2 + 1, GFP_KERNEL);
>> +	if (!hash)
>> +		return;
>> +	p = memcpy(hash, "tbs:", 4);
>> +	p += 4;
>> +	bin2hex(p, data, len);
>> +	p += len * 2;
>> +	*p = 0;
>> +
>> +	mark_hash_blacklisted(hash);
>> +	kfree(hash);
>> +}
>> +
>> +/*
>> + * Blacklist the hash of an executable.
>> + */
>> +static __init void uefi_blacklist_binary(const char *source,
>> +					 const void *data, size_t len)
>> +{
>> +	char *hash, *p;
>> +
>> +	hash = kmalloc(4 + len * 2 + 1, GFP_KERNEL);
>> +	if (!hash)
>> +		return;
>> +	p = memcpy(hash, "bin:", 4);
>> +	p += 4;
>> +	bin2hex(p, data, len);
>> +	p += len * 2;
>> +	*p = 0;
>> +
>> +	mark_hash_blacklisted(hash);
>> +	kfree(hash);
>> +}
>>
> These could be refactored into one function.
>
>

Thanks James for reviewing.

Yes, the code should be refactored.  However, I think making it a single 
function would require adding a new field to the function callback 
definitions as well. Probably, a simpler approach would be to define a 
common function uefi_blacklist_hash(...)  which can then be used by the 
two functions uefi_blacklist_x509_tbs(...) and 
uefi_blacklist_binary(...). These two functions now act as wrapper 
functions. Below is the example code:

+/*
+ * Blacklist a hash.
+ */
+static __init void uefi_blacklist_hash(const char *source, const void 
*data,
+                                 size_t len, char *type, size_t type_len)
+{
+       char *hash, *p;
+
+       hash = kmalloc(type_len + len * 2 + 1, GFP_KERNEL);
+       if (!hash)
+               return;
+       p = memcpy(hash, type, type_len);
+       p += type_len;
+       bin2hex(p, data, len);
+       p += len * 2;
+       *p = 0;
+
+       mark_hash_blacklisted(hash);
+       kfree(hash);
+}
+
+/*
+ * Blacklist an X509 TBS hash.
+ */
+static __init void uefi_blacklist_x509_tbs(const char *source,
+                                          const void *data, size_t len)
+{
+       uefi_blacklist_hash(source, data, len, "tbs:" , 4);
+}
+
+/*
+ * Blacklist the hash of an executable.
+ */
+static __init void uefi_blacklist_binary(const char *source,
+                                        const void *data, size_t len)
+{
+       uefi_blacklist_hash(source, data, len, "bin:" , 4);
+}


Thanks & Regards,
    - Nayna