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KEYS: fixes for asym_tpm keys

PATCH In review Eric Biggers 3 participants 14 messages Jan 13, 2022 – Feb 8, 2022

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Stable branch Crypto API Keys/keyrings Asymmetric keys
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Eric Biggers

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#0 lore raw

cover KEYS: fixes for asym_tpm keys

This series fixes some bugs in asym_tpm.c.

Eric Biggers (3):
KEYS: asym_tpm: fix buffer overreads in extract_key_parameters()
KEYS: asym_tpm: fix incorrect comment
KEYS: asym_tpm: rename derive_pub_key()

 crypto/asymmetric_keys/asym_tpm.c | 44 +++++++++++++++++++------------
 1 file changed, 27 insertions(+), 17 deletions(-)

base-commit: feb7a43de5ef625ad74097d8fd3481d5dbc06a59

Signature · 1 line
2.34.1
author
#1 lore raw

PATCH 1/3 KEYS: asym_tpm: fix buffer overreads in extract_key_parameters()

From: Eric Biggers <[email protected]>

extract_key_parameters() can read past the end of the input buffer due to buggy and missing bounds checks. Fix it as follows:

- Before reading each key length field, verify that there are at least 4 bytes remaining.

- Avoid integer overflows when validating size fields; 'sz + 12' and '4 + sz' overflowed if 'sz' is near U32_MAX.

- Before saving the pointer to the public key, check that it doesn't run past the end of the buffer.

Fixes f8c54e1ac4b8 ("KEYS: asym_tpm: extract key size & public key [ver #2]")
Cc <[email protected]> # v4.20+
Signed-off-by Eric Biggers <[email protected]>
---
 crypto/asymmetric_keys/asym_tpm.c | 30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)
crypto/asymmetric_keys/asym_tpm.c +18 -12
index 0959613560b9..60d20d44c885 100644
@@ -814,7 +814,6 @@ static int extract_key_parameters(struct tpm_key *tk)
 {
 	const void *cur = tk->blob;
 	uint32_t len = tk->blob_len;
-	const void *pub_key;
 	uint32_t sz;
 	uint32_t key_len;
 

@@ -845,14 +844,14 @@ static int extract_key_parameters(struct tpm_key *tk)
 		return -EBADMSG;
 
 	sz = get_unaligned_be32(cur + 8);
-	if (len < sz + 12)
-		return -EBADMSG;
 
 	/* Move to TPM_RSA_KEY_PARMS */
-	len -= 12;
 	cur += 12;
+	len -= 12;
 
 	/* Grab the RSA key length */
+	if (len < 4)
+		return -EBADMSG;
 	key_len = get_unaligned_be32(cur);
 
 	switch (key_len) {

@@ -866,29 +865,36 @@ static int extract_key_parameters(struct tpm_key *tk)
 	}
 
 	/* Move just past TPM_KEY_PARMS */
+	if (len < sz)
+		return -EBADMSG;
 	cur += sz;
 	len -= sz;
 
 	if (len < 4)
 		return -EBADMSG;
-
 	sz = get_unaligned_be32(cur);
-	if (len < 4 + sz)
-		return -EBADMSG;
+	cur += 4;
+	len -= 4;
 
 	/* Move to TPM_STORE_PUBKEY */
-	cur += 4 + sz;
-	len -= 4 + sz;
+	if (len < sz)
+		return -EBADMSG;
+	cur += sz;
+	len -= sz;
 
 	/* Grab the size of the public key, it should jive with the key size */
+	if (len < 4)
+		return -EBADMSG;
 	sz = get_unaligned_be32(cur);
+	cur += 4;
+	len -= 4;
 	if (sz > 256)
 		return -EINVAL;
-
-	pub_key = cur + 4;
+	if (len < sz)
+		return -EBADMSG;
 
 	tk->key_len = key_len;
-	tk->pub_key = pub_key;
+	tk->pub_key = cur;
 	tk->pub_key_len = sz;
 
 	return 0;
Signature · 1 line
2.34.1
maintainer
#2 lore raw

Re: [PATCH 1/3] KEYS: asym_tpm: fix buffer overreads in extract_key_parameters()

Quoted 7 lines · Eric Biggers

From: Eric Biggers <[email protected]>

extract_key_parameters() can read past the end of the input buffer due to buggy and missing bounds checks. Fix it as follows:

- Before reading each key length field, verify that there are at least 4 bytes remaining.

Maybe start with a "Key length is described as an unsigned 32-bit integer in the TPM header". Just for clarity.

Quoted 3 lines

- Avoid integer overflows when validating size fields; 'sz + 12' and '4 + sz' overflowed if 'sz' is near U32_MAX.

So we have a struct tpm_header in include/linux/tpm.h. It would be way more informative to use sizeof(struct tpm_header) than number 12, even if the patch does not otherwise use the struct. It tells what it is, 12 does not.

Quoted 6 lines

- Before saving the pointer to the public key, check that it doesn't run past the end of the buffer.

Fixes f8c54e1ac4b8 ("KEYS: asym_tpm: extract key size & public key [ver #2]")
Cc <[email protected]> # v4.20+
Signed-off-by Eric Biggers <[email protected]>

BR, Jarkko

author
#3 lore raw

Re: [PATCH 1/3] KEYS: asym_tpm: fix buffer overreads in extract_key_parameters()

Quoted 8 lines · Jarkko Sakkinen
Quoted 3 lines

- Avoid integer overflows when validating size fields; 'sz + 12' and '4 + sz' overflowed if 'sz' is near U32_MAX.

So we have a struct tpm_header in include/linux/tpm.h. It would be way more informative to use sizeof(struct tpm_header) than number 12, even if the patch does not otherwise use the struct. It tells what it is, 12 does not.

I don't think that would be an improvement, given that the code is using hard-coded offsets. If it's reading 4 bytes from cur + 8, it's much easier to understand that it needs 12 bytes than 'sizeof(struct tpm_header)' bytes.

I'd certainly encourage whoever is maintaining this code to change it to use structs instead, but that's not what this patch is meant to do.

- Eric

maintainer
#4 lore raw

Re: [PATCH 1/3] KEYS: asym_tpm: fix buffer overreads in extract_key_parameters()

Quoted 10 lines · Eric Biggers
Quoted 8 lines · Jarkko Sakkinen
Quoted 3 lines

- Avoid integer overflows when validating size fields; 'sz + 12' and '4 + sz' overflowed if 'sz' is near U32_MAX.

So we have a struct tpm_header in include/linux/tpm.h. It would be way more informative to use sizeof(struct tpm_header) than number 12, even if the patch does not otherwise use the struct. It tells what it is, 12 does not.

Quoted 6 lines

I don't think that would be an improvement, given that the code is using hard-coded offsets. If it's reading 4 bytes from cur + 8, it's much easier to understand that it needs 12 bytes than 'sizeof(struct tpm_header)' bytes.

I'd certainly encourage whoever is maintaining this code to change it to use structs instead, but that's not what this patch is meant to do.

I would consider dropping asym_tpm as it has no practical use cases existing.

/Jarkko

maintainer
#5 lore raw

Re: [PATCH 1/3] KEYS: asym_tpm: fix buffer overreads in extract_key_parameters()

Quoted 15 lines · Jarkko Sakkinen
Quoted 14 lines · Eric Biggers
Quoted 8 lines · Jarkko Sakkinen
Quoted 3 lines

- Avoid integer overflows when validating size fields; 'sz + 12' and '4 + sz' overflowed if 'sz' is near U32_MAX.

So we have a struct tpm_header in include/linux/tpm.h. It would be way more informative to use sizeof(struct tpm_header) than number 12, even if the patch does not otherwise use the struct. It tells what it is, 12 does not.

I don't think that would be an improvement, given that the code is using hard-coded offsets. If it's reading 4 bytes from cur + 8, it's much easier to understand that it needs 12 bytes than 'sizeof(struct tpm_header)' bytes.

Quoted 5 lines
Quoted 2 lines

I'd certainly encourage whoever is maintaining this code to change it to use structs instead, but that's not what this patch is meant to do.

I would consider dropping asym_tpm as it has no practical use cases existing.

At least I have zero motivation to maintain it as it does not meet any quality standards and is based on insecure crypto algorithms. I neither have participated to its review process.

/Jarkko

author
#6 lore raw

Re: [PATCH 1/3] KEYS: asym_tpm: fix buffer overreads in extract_key_parameters()

Quoted 19 lines · Jarkko Sakkinen
Quoted 18 lines · Jarkko Sakkinen
Quoted 16 lines · Eric Biggers
Quoted 8 lines · Jarkko Sakkinen
Quoted 3 lines

- Avoid integer overflows when validating size fields; 'sz + 12' and '4 + sz' overflowed if 'sz' is near U32_MAX.

So we have a struct tpm_header in include/linux/tpm.h. It would be way more informative to use sizeof(struct tpm_header) than number 12, even if the patch does not otherwise use the struct. It tells what it is, 12 does not.

I don't think that would be an improvement, given that the code is using hard-coded offsets. If it's reading 4 bytes from cur + 8, it's much easier to understand that it needs 12 bytes than 'sizeof(struct tpm_header)' bytes.

I'd certainly encourage whoever is maintaining this code to change it to use structs instead, but that's not what this patch is meant to do.

Quoted 6 lines
Quoted 2 lines

I would consider dropping asym_tpm as it has no practical use cases existing.

At least I have zero motivation to maintain it as it does not meet any quality standards and is based on insecure crypto algorithms. I neither have participated to its review process.

Fair enough, I'll send a patch to remove it then.

- Eric

maintainer
#7 lore raw

Re: [PATCH 1/3] KEYS: asym_tpm: fix buffer overreads in extract_key_parameters()

Quoted 20 lines · Eric Biggers
Quoted 19 lines · Jarkko Sakkinen
Quoted 18 lines · Jarkko Sakkinen
Quoted 16 lines · Eric Biggers
Quoted 8 lines · Jarkko Sakkinen
Quoted 3 lines

- Avoid integer overflows when validating size fields; 'sz + 12' and '4 + sz' overflowed if 'sz' is near U32_MAX.

So we have a struct tpm_header in include/linux/tpm.h. It would be way more informative to use sizeof(struct tpm_header) than number 12, even if the patch does not otherwise use the struct. It tells what it is, 12 does not.

I don't think that would be an improvement, given that the code is using hard-coded offsets. If it's reading 4 bytes from cur + 8, it's much easier to understand that it needs 12 bytes than 'sizeof(struct tpm_header)' bytes.

I'd certainly encourage whoever is maintaining this code to change it to use structs instead, but that's not what this patch is meant to do.

Quoted 8 lines
Quoted 6 lines
Quoted 2 lines

I would consider dropping asym_tpm as it has no practical use cases existing.

At least I have zero motivation to maintain it as it does not meet any quality standards and is based on insecure crypto algorithms. I neither have participated to its review process.

Fair enough, I'll send a patch to remove it then.

It is IMHO. I mean having this advertising insecure ways to to do crypto.

Thank you.

PS. My latency is because I've been moving to a new job. It is temporary.

/Jarkko

author
#8 lore raw

PATCH 2/3 KEYS: asym_tpm: fix incorrect comment

In reply to Eric Biggers

From: Eric Biggers <[email protected]>

tpm_key_create() doesn't actually load the key into the TPM. Fix the comment to describe what the function does.

Signed-off-by Eric Biggers <[email protected]>
---
 crypto/asymmetric_keys/asym_tpm.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
crypto/asymmetric_keys/asym_tpm.c +5 -1
index 60d20d44c885..2e365a221fbe 100644
@@ -900,7 +900,11 @@ static int extract_key_parameters(struct tpm_key *tk)
 	return 0;
 }
 
-/* Given the blob, parse it and load it into the TPM */
+/*
+ * Verify that a supported TPM is present, then parse the key blob.  We don't
+ * actually load the key into the TPM here; that happens only for the actual
+ * sign and decrypt operations.
+ */
 struct tpm_key *tpm_key_create(const void *blob, uint32_t blob_len)
 {
 	int r;
Signature · 1 line
2.34.1
maintainer Acked-by on v1 2/3
#9 lore raw

Re: [PATCH 2/3] KEYS: asym_tpm: fix incorrect comment

Quoted 6 lines · Eric Biggers

From: Eric Biggers <[email protected]>

tpm_key_create() doesn't actually load the key into the TPM. Fix the comment to describe what the function does.

Signed-off-by Eric Biggers <[email protected]>
Acked-by Jarkko Sakkinen <[email protected]>

This asym_tpm has not been properly reviewed as far as I can tell.

For starters, I do not get who needed new TPM 1.x features in 2018... It's long after SHA1 was declared as insecure and world was mostly settled with TPM2.

BR, Jarkko

author
#10 lore raw

PATCH 3/3 KEYS: asym_tpm: rename derive_pub_key()

In reply to Eric Biggers

From: Eric Biggers <[email protected]>

derive_pub_key() doesn't actually derive a key; it just formats one. Rename it accordingly.

Signed-off-by Eric Biggers <[email protected]>
---
 crypto/asymmetric_keys/asym_tpm.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
crypto/asymmetric_keys/asym_tpm.c +4 -4
index 2e365a221fbe..d2e0036d34a5 100644
@@ -336,7 +336,7 @@ static inline uint8_t *encode_tag_length(uint8_t *buf, uint8_t tag,
 	return buf + 3;
 }
 
-static uint32_t derive_pub_key(const void *pub_key, uint32_t len, uint8_t *buf)
+static uint32_t format_pub_key(const void *pub_key, uint32_t len, uint8_t *buf)
 {
 	uint8_t *cur = buf;
 	uint32_t n_len = definite_length(len) + 1 + len + 1;

@@ -409,7 +409,7 @@ static int tpm_key_query(const struct kernel_pkey_params *params,
 	if (IS_ERR(tfm))
 		return PTR_ERR(tfm);
 
-	der_pub_key_len = derive_pub_key(tk->pub_key, tk->pub_key_len,
+	der_pub_key_len = format_pub_key(tk->pub_key, tk->pub_key_len,
 					 der_pub_key);
 
 	ret = crypto_akcipher_set_pub_key(tfm, der_pub_key, der_pub_key_len);

@@ -463,7 +463,7 @@ static int tpm_key_encrypt(struct tpm_key *tk,
 	if (IS_ERR(tfm))
 		return PTR_ERR(tfm);
 
-	der_pub_key_len = derive_pub_key(tk->pub_key, tk->pub_key_len,
+	der_pub_key_len = format_pub_key(tk->pub_key, tk->pub_key_len,
 					 der_pub_key);
 
 	ret = crypto_akcipher_set_pub_key(tfm, der_pub_key, der_pub_key_len);

@@ -758,7 +758,7 @@ static int tpm_key_verify_signature(const struct key *key,
 	if (IS_ERR(tfm))
 		return PTR_ERR(tfm);
 
-	der_pub_key_len = derive_pub_key(tk->pub_key, tk->pub_key_len,
+	der_pub_key_len = format_pub_key(tk->pub_key, tk->pub_key_len,
 					 der_pub_key);
 
 	ret = crypto_akcipher_set_pub_key(tfm, der_pub_key, der_pub_key_len);
Signature · 1 line
2.34.1
Reviewed-by on the v1 series
#12 lore raw
In reply to Eric Biggers

Hi Eric,

Quoted 7 lines · Eric Biggers

This series fixes some bugs in asym_tpm.c.

Eric Biggers (3):
KEYS: asym_tpm: fix buffer overreads in extract_key_parameters()
KEYS: asym_tpm: fix incorrect comment
KEYS: asym_tpm: rename derive_pub_key()

Quoted 6 lines
  crypto/asymmetric_keys/asym_tpm.c | 44 +++++++++++++++++++------------
  1 file changed, 27 insertions(+), 17 deletions(-)

base-commit: feb7a43de5ef625ad74097d8fd3481d5dbc06a59

For the series:

Reviewed-by Denis Kenzior <[email protected]>

Regards,
-Denis

maintainer
#13 lore raw
In reply to Eric Biggers
Quoted 7 lines · Eric Biggers

This series fixes some bugs in asym_tpm.c.

Eric Biggers (3):
KEYS: asym_tpm: fix buffer overreads in extract_key_parameters()
KEYS: asym_tpm: fix incorrect comment
KEYS: asym_tpm: rename derive_pub_key()

Quoted 8 lines
 crypto/asymmetric_keys/asym_tpm.c | 44 +++++++++++++++++++------------
 1 file changed, 27 insertions(+), 17 deletions(-)

base-commit: feb7a43de5ef625ad74097d8fd3481d5dbc06a59

Signature · 1 line
2.34.1

I really appreciate your effort to go and fix this key type. Thank you.

BR, Jarkko