Re: [PATCH v9 1/4] KEYS: trusted: Add generic trusted keys framework

[James Bottomley <jejb@linux.ibm.com>]

On Mon, 2021-03-01 at 18:41 +0530, Sumit Garg wrote:
> Current trusted keys framework is tightly coupled to use TPM device
> as an underlying implementation which makes it difficult for
> implementations like Trusted Execution Environment (TEE) etc. to
> provide trusted keys support in case platform doesn't posses a TPM
> device.
> 
> Add a generic trusted keys framework where underlying implementations
> can be easily plugged in. Create struct trusted_key_ops to achieve
> this, which contains necessary functions of a backend.
> 
> Also, define a module parameter in order to select a particular trust
> source in case a platform support multiple trust sources. In case its
> not specified then implementation itetrates through trust sources
> list starting with TPM and assign the first trust source as a backend
> which has initiazed successfully during iteration.
> 
> Note that current implementation only supports a single trust source
> at runtime which is either selectable at compile time or during boot
> via aforementioned module parameter.

You never actually tested this, did you?  I'm now getting EINVAL from
all the trusted TPM key operations because of this patch.

The reason is quite simple:  this function:

> index 000000000000..0db86b44605d
> --- /dev/null
> +++ b/security/keys/trusted-keys/trusted_core.c
[...]
> +static int datablob_parse(char *datablob, struct trusted_key_payload
> *p)
> +{
> +	substring_t args[MAX_OPT_ARGS];
> +	long keylen;
> +	int ret = -EINVAL;
> +	int key_cmd;
> +	char *c;
> +
> +	/* main command */
> +	c = strsep(&datablob, " \t");

Modifies its argument to consume tokens and separates them with NULL.

so the arguments for

keyctl add trusted kmk "new 34 keyhandle=0x81000001"

Go into this function as

datablob="new 34 keyhandle=0x81000001"

After we leave it, it looks like

datablob="new\034\0keyhandle=0x81000001"

However here:

> +static int trusted_instantiate(struct key *key,
> +			       struct key_preparsed_payload *prep)
> +{
> +	struct trusted_key_payload *payload = NULL;
> +	size_t datalen = prep->datalen;
> +	char *datablob;
> +	int ret = 0;
> +	int key_cmd;
> +	size_t key_len;
> +
> +	if (datalen <= 0 || datalen > 32767 || !prep->data)
> +		return -EINVAL;
> +
> +	datablob = kmalloc(datalen + 1, GFP_KERNEL);
> +	if (!datablob)
> +		return -ENOMEM;
> +	memcpy(datablob, prep->data, datalen);
> +	datablob[datalen] = '\0';
> +
> +	payload = trusted_payload_alloc(key);
> +	if (!payload) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +
> +	key_cmd = datablob_parse(datablob, payload);
> +	if (key_cmd < 0) {
> +		ret = key_cmd;
> +		goto out;
> +	}
> +
> +	dump_payload(payload);
> +
> +	switch (key_cmd) {
> +	case Opt_load:
> +		ret = static_call(trusted_key_unseal)(payload,
> datablob);

We're passing the unmodified

datablob="new\034\0keyhandle=0x81000001"

Into the tpm trusted_key_unseal function.  However, it only sees "new"
and promply gives EINVAL because you've removed the ability to process
the new option from it.  What should have happened is you should have
moved data blob up to passed the consumed tokens, so it actually reads

datablob="keyhandle=0x81000001"

However, to do that you'd have to have the updated pointer passed out
of your datablob_parse() above.

There's also a lost !tpm2 in the check for options->keyhandle, but I
suspect Jarkko lost that merging the two patches.  I think what's below
fixes all of this, so if you can test it for trusted_tee, I'll package
it up as two separate patches fixing all of this.

James

---

diff --git a/security/keys/trusted-keys/trusted_core.c b/security/keys/trusted-keys/trusted_core.c
index ec3a066a4b42..7c636212429b 100644
--- a/security/keys/trusted-keys/trusted_core.c
+++ b/security/keys/trusted-keys/trusted_core.c
@@ -62,7 +62,7 @@ static const match_table_t key_tokens = {
  *
  * On success returns 0, otherwise -EINVAL.
  */
-static int datablob_parse(char *datablob, struct trusted_key_payload *p)
+static int datablob_parse(char **datablob, struct trusted_key_payload *p)
 {
 	substring_t args[MAX_OPT_ARGS];
 	long keylen;
@@ -71,14 +71,14 @@ static int datablob_parse(char *datablob, struct trusted_key_payload *p)
 	char *c;
 
 	/* main command */
-	c = strsep(&datablob, " \t");
+	c = strsep(datablob, " \t");
 	if (!c)
 		return -EINVAL;
 	key_cmd = match_token(c, key_tokens, args);
 	switch (key_cmd) {
 	case Opt_new:
 		/* first argument is key size */
-		c = strsep(&datablob, " \t");
+		c = strsep(datablob, " \t");
 		if (!c)
 			return -EINVAL;
 		ret = kstrtol(c, 10, &keylen);
@@ -89,7 +89,7 @@ static int datablob_parse(char *datablob, struct trusted_key_payload *p)
 		break;
 	case Opt_load:
 		/* first argument is sealed blob */
-		c = strsep(&datablob, " \t");
+		c = strsep(datablob, " \t");
 		if (!c)
 			return -EINVAL;
 		p->blob_len = strlen(c) / 2;
@@ -138,7 +138,7 @@ static int trusted_instantiate(struct key *key,
 {
 	struct trusted_key_payload *payload = NULL;
 	size_t datalen = prep->datalen;
-	char *datablob;
+	char *datablob, *orig_datablob;
 	int ret = 0;
 	int key_cmd;
 	size_t key_len;
@@ -146,7 +146,7 @@ static int trusted_instantiate(struct key *key,
 	if (datalen <= 0 || datalen > 32767 || !prep->data)
 		return -EINVAL;
 
-	datablob = kmalloc(datalen + 1, GFP_KERNEL);
+	orig_datablob = datablob = kmalloc(datalen + 1, GFP_KERNEL);
 	if (!datablob)
 		return -ENOMEM;
 	memcpy(datablob, prep->data, datalen);
@@ -158,7 +158,7 @@ static int trusted_instantiate(struct key *key,
 		goto out;
 	}
 
-	key_cmd = datablob_parse(datablob, payload);
+	key_cmd = datablob_parse(&datablob, payload);
 	if (key_cmd < 0) {
 		ret = key_cmd;
 		goto out;
@@ -194,7 +194,7 @@ static int trusted_instantiate(struct key *key,
 		ret = -EINVAL;
 	}
 out:
-	kfree_sensitive(datablob);
+	kfree_sensitive(orig_datablob);
 	if (!ret)
 		rcu_assign_keypointer(key, payload);
 	else
@@ -218,7 +218,7 @@ static int trusted_update(struct key *key, struct key_preparsed_payload *prep)
 	struct trusted_key_payload *p;
 	struct trusted_key_payload *new_p;
 	size_t datalen = prep->datalen;
-	char *datablob;
+	char *datablob, *orig_datablob;
 	int ret = 0;
 
 	if (key_is_negative(key))
@@ -229,7 +229,7 @@ static int trusted_update(struct key *key, struct key_preparsed_payload *prep)
 	if (datalen <= 0 || datalen > 32767 || !prep->data)
 		return -EINVAL;
 
-	datablob = kmalloc(datalen + 1, GFP_KERNEL);
+	orig_datablob = datablob = kmalloc(datalen + 1, GFP_KERNEL);
 	if (!datablob)
 		return -ENOMEM;
 
@@ -241,7 +241,7 @@ static int trusted_update(struct key *key, struct key_preparsed_payload *prep)
 
 	memcpy(datablob, prep->data, datalen);
 	datablob[datalen] = '\0';
-	ret = datablob_parse(datablob, new_p);
+	ret = datablob_parse(&datablob, new_p);
 	if (ret != Opt_update) {
 		ret = -EINVAL;
 		kfree_sensitive(new_p);
@@ -265,7 +265,7 @@ static int trusted_update(struct key *key, struct key_preparsed_payload *prep)
 	rcu_assign_keypointer(key, new_p);
 	call_rcu(&p->rcu, trusted_rcu_free);
 out:
-	kfree_sensitive(datablob);
+	kfree_sensitive(orig_datablob);
 	return ret;
 }
 
diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c
index 4e5c50138f92..bc702ba0a596 100644
--- a/security/keys/trusted-keys/trusted_tpm1.c
+++ b/security/keys/trusted-keys/trusted_tpm1.c
@@ -747,6 +747,9 @@ static int getoptions(char *c, struct trusted_key_payload *pay,
 
 	opt->hash = tpm2 ? HASH_ALGO_SHA256 : HASH_ALGO_SHA1;
 
+	if (!c)
+		return 0;
+
 	while ((p = strsep(&c, " \t"))) {
 		if (*p == '\0' || *p == ' ' || *p == '\t')
 			continue;
@@ -944,7 +947,7 @@ static int trusted_tpm_unseal(struct trusted_key_payload *p, char *datablob)
 		goto out;
 	dump_options(options);
 
-	if (!options->keyhandle) {
+	if (!options->keyhandle && !tpm2) {
 		ret = -EINVAL;
 		goto out;
 	}