Fix bugs in public_key_verify_signature()
Subsystems (5)
v2 cover Fix bugs in public_key_verify_signature()
This patchset fixes some bugs in public_key_verify_signature() where it could be tricked into using the wrong algorithm, as was discussed at
https://lore.kernel.org/linux-integrity/[email protected]/T/#t
I'd appreciate it if the people who care about each of the supported public key algorithms (RSA, ECDSA, ECRDSA, and SM2) would test this patchset to make sure it still works for their use case(s). I've tested that X.509 and PKCS#7 with RSA still work.
Note, I have *not* included a fix for SM2 being implemented incorrectly. That is another bug that I pointed out in the above thread. I think that bug is for the people who actually care about SM2.
This applies to v5.17-rc3.
Changed v1 => v2:
- Changed patch 1 to continue allowing a NULL sig->pkey_algo.
Eric Biggers (2):
KEYS: asymmetric: enforce that sig algo matches key algo
KEYS: asymmetric: properly validate hash_algo and encoding
crypto/asymmetric_keys/pkcs7_verify.c | 6 -- crypto/asymmetric_keys/public_key.c | 126 ++++++++++++++++------- crypto/asymmetric_keys/x509_public_key.c | 6 -- 3 files changed, 91 insertions(+), 47 deletions(-)
base-commit: dfd42facf1e4ada021b939b4e19c935dcdd55566
Signature · 1 line
2.35.1
PATCH v2 1/2 KEYS: asymmetric: enforce that sig algo matches key algo
From: Eric Biggers <[email protected]>
Most callers of public_key_verify_signature(), including most indirect callers via verify_signature() as well as pkcs7_verify_sig_chain(), don't check that public_key_signature::pkey_algo matches public_key::pkey_algo. These should always match. However, a malicious signature could intentionally declare an unintended algorithm. It is essential that such signatures be rejected outright, or that the algorithm of the *key* be used -- not the algorithm of the signature as that would allow attackers to choose the algorithm used.
Currently, public_key_verify_signature() correctly uses the key's algorithm when deciding which akcipher to allocate. That's good. However, it uses the signature's algorithm when deciding whether to do the first step of SM2, which is incorrect. Also, v4.19 and older kernels used the signature's algorithm for the entire process.
Prevent such errors by making public_key_verify_signature() enforce that the signature's algorithm (if given) matches the key's algorithm.
Also remove two checks of this done by callers, which are now redundant.
--- crypto/asymmetric_keys/pkcs7_verify.c | 6 ------ crypto/asymmetric_keys/public_key.c | 15 +++++++++++++++ crypto/asymmetric_keys/x509_public_key.c | 6 ------ 3 files changed, 15 insertions(+), 12 deletions(-)
crypto/asymmetric_keys/pkcs7_verify.c +0 -6
@@ -174,12 +174,6 @@ static int pkcs7_find_key(struct pkcs7_message *pkcs7,pr_devel ("Sig %u: Found cert serial match X.509[%u]\n" , sinfo->index, certix); -if (strcmp (x509->pub->pkey_algo, sinfo->sig->pkey_algo) !=0 ) { -pr_warn ("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n" , - sinfo->index); -continue ; - } - sinfo->signer = x509;return 0 ; }
crypto/asymmetric_keys/public_key.c +15 -0
@@ -325,6 +325,21 @@ int public_key_verify_signature(const struct public_key *pkey,BUG_ON (!sig);BUG_ON (!sig->s); +/* +* If the signature specifies a public key algorithm, it *must* match +* the key's actual public key algorithm. +* +* Small exception: ECDSA signatures don't specify the curve, but ECDSA +* keys do. So the strings can mismatch slightly in that case: +* "ecdsa-nist-*" for the key, but "ecdsa" for the signature. +*/ +if (sig->pkey_algo) { +if (strcmp (pkey->pkey_algo, sig->pkey_algo) !=0 && + (strncmp (pkey->pkey_algo,"ecdsa-" ,6 ) !=0 || +strcmp (sig->pkey_algo,"ecdsa" ) !=0 )) +return -EKEYREJECTED ; + } + ret =software_key_determine_akcipher (sig->encoding, sig->hash_algo, pkey, alg_name);
crypto/asymmetric_keys/x509_public_key.c +0 -6
@@ -128,12 +128,6 @@ int x509_check_for_self_signed(struct x509_certificate *cert) goto out; } - ret = -EKEYREJECTED ; -if (strcmp (cert->pub->pkey_algo, cert->sig->pkey_algo) !=0 && - (strncmp (cert->pub->pkey_algo,"ecdsa-" ,6 ) !=0 || -strcmp (cert->sig->pkey_algo,"ecdsa" ) !=0 )) - goto out; - ret =public_key_verify_signature (cert->pub, cert->sig);if (ret <0 ) {if (ret == -ENOPKG ) {
Signature · 1 line
2.35.1
Re: [PATCH v2 1/2] KEYS: asymmetric: enforce that sig algo matches key algo
Quoted 20 lines · Eric Biggers
From: Eric Biggers <[email protected]>
Most callers of
public_key_verify_signature(), including most indirect callers viaverify_signature()as well aspkcs7_verify_sig_chain(), don't check thatpublic_key_signature::pkey_algomatchespublic_key::pkey_algo. These should always match. However, a malicious signature could intentionally declare an unintended algorithm. It is essential that such signatures be rejected outright, or that the algorithm of the *key* be used -- not the algorithm of the signature as that would allow attackers to choose the algorithm used.Currently,
public_key_verify_signature()correctly uses the key's algorithm when deciding which akcipher to allocate. That's good. However, it uses the signature's algorithm when deciding whether to do the first step of SM2, which is incorrect. Also, v4.19 and older kernels used the signature's algorithm for the entire process.Prevent such errors by making
public_key_verify_signature()enforce that the signature's algorithm (if given) matches the key's algorithm.
Quoted 6 lines
Also remove two checks of this done by callers, which are now redundant.
Tested-by Stefan Berger <[email protected]>Tested-by Tianjia Zhang <[email protected]>Signed-off-by Eric Biggers <[email protected]>
Thanks,
Quoted 68 lines
--- crypto/asymmetric_keys/pkcs7_verify.c | 6 ------ crypto/asymmetric_keys/public_key.c | 15 +++++++++++++++ crypto/asymmetric_keys/x509_public_key.c | 6 ------ 3 files changed, 15 insertions(+), 12 deletions(-)crypto/asymmetric_keys/pkcs7_verify.c +0
-6@@ -174,12 +174,6 @@ static int pkcs7_find_key(struct pkcs7_message *pkcs7,pr_devel ("Sig %u: Found cert serial match X.509[%u]\n" , sinfo->index, certix); -if (strcmp (x509->pub->pkey_algo, sinfo->sig->pkey_algo) !=0 ) { -pr_warn ("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n" , - sinfo->index); -continue ; - } - sinfo->signer = x509;return 0 ; }crypto/asymmetric_keys/public_key.c +15
-0@@ -325,6 +325,21 @@ int public_key_verify_signature(const struct public_key *pkey,BUG_ON (!sig);BUG_ON (!sig->s); +/* +* If the signature specifies a public key algorithm, it *must* match +* the key's actual public key algorithm. +* +* Small exception: ECDSA signatures don't specify the curve, but ECDSA +* keys do. So the strings can mismatch slightly in that case: +* "ecdsa-nist-*" for the key, but "ecdsa" for the signature. +*/ +if (sig->pkey_algo) { +if (strcmp (pkey->pkey_algo, sig->pkey_algo) !=0 && + (strncmp (pkey->pkey_algo,"ecdsa-" ,6 ) !=0 || +strcmp (sig->pkey_algo,"ecdsa" ) !=0 )) +return -EKEYREJECTED ; + } + ret =software_key_determine_akcipher (sig->encoding, sig->hash_algo, pkey, alg_name);crypto/asymmetric_keys/x509_public_key.c +0
-6@@ -128,12 +128,6 @@ int x509_check_for_self_signed(struct x509_certificate *cert) goto out; } - ret = -EKEYREJECTED ; -if (strcmp (cert->pub->pkey_algo, cert->sig->pkey_algo) !=0 && - (strncmp (cert->pub->pkey_algo,"ecdsa-" ,6 ) !=0 || -strcmp (cert->sig->pkey_algo,"ecdsa" ) !=0 )) - goto out; - ret =public_key_verify_signature (cert->pub, cert->sig);if (ret <0 ) {if (ret == -ENOPKG ) {Signature · 1 line
2.35.1
PATCH v2 2/2 KEYS: asymmetric: properly validate hash_algo and encoding
In reply to Eric BiggersFrom: Eric Biggers <[email protected]>
It is insecure to allow arbitrary hash algorithms and signature encodings to be used with arbitrary signature algorithms. Notably, ECDSA, ECRDSA, and SM2 all sign/verify raw hash values and don't disambiguate between different hash algorithms like RSA PKCS#1 v1.5 padding does. Therefore, they need to be restricted to certain sets of hash algorithms (ideally just one, but in practice small sets are used). Additionally, the encoding is an integral part of modern signature algorithms, and is not supposed to vary.
Therefore, tighten the checks of hash_algo and encoding done by software_key_determine_akcipher().
Also rearrange the parameters to software_key_determine_akcipher() to put the public_key first, as this is the most important parameter and it often determines everything else.
--- crypto/asymmetric_keys/public_key.c | 111 +++++++++++++++++++--------- 1 file changed, 76 insertions(+), 35 deletions(-)
crypto/asymmetric_keys/public_key.c +76 -35
@@ -60,39 +60,83 @@ static void public_key_destroy(void *payload0, void *payload3) }/* -* Determine the crypto algorithm name. +* Given a public_key, and an encoding and hash_algo to be used for signing +* and/or verification with that key, determine the name of the corresponding +* akcipher algorithm. Also check that encoding and hash_algo are allowed. */ -static -int software_key_determine_akcipher (const char *encoding, -const char *hash_algo, -const struct public_key *pkey, -char alg_name[CRYPTO_MAX_ALG_NAME ]) +static int +software_key_determine_akcipher (const struct public_key *pkey, +const char *encoding,const char *hash_algo, +char alg_name[CRYPTO_MAX_ALG_NAME ]) {int n; -if (strcmp (encoding,"pkcs1" ) ==0 ) { -/* The data wangled by the RSA algorithm is typically padded -* and encoded in some manner, such as EMSA-PKCS1-1_5 [RFC3447 -* sec 8.2]. +if (!encoding) +return -EINVAL ; + +if (strcmp (pkey->pkey_algo,"rsa" ) ==0 ) { +/* +* RSA signatures usually use EMSA-PKCS1-1_5 [RFC3447 sec 8.2]. +*/ +if (strcmp (encoding,"pkcs1" ) ==0 ) { +if (!hash_algo) + n =snprintf (alg_name,CRYPTO_MAX_ALG_NAME , +"pkcs1pad(%s)" , + pkey->pkey_algo); +else + n =snprintf (alg_name,CRYPTO_MAX_ALG_NAME , +"pkcs1pad(%s,%s)" , + pkey->pkey_algo, hash_algo); +return n >=CRYPTO_MAX_ALG_NAME ? -EINVAL :0 ; + } +if (strcmp (encoding,"raw" ) !=0 ) +return -EINVAL ; +/* +* Raw RSA cannot differentiate between different hash +* algorithms. +*/ +if (hash_algo) +return -EINVAL ; + }else if (strncmp (pkey->pkey_algo,"ecdsa" ,5 ) ==0 ) { +if (strcmp (encoding,"x962" ) !=0 ) +return -EINVAL ; +/* +* ECDSA signatures are taken over a raw hash, so they don't +* differentiate between different hash algorithms. That means +* that the verifier should hard-code a specific hash algorithm. +* Unfortunately, in practice ECDSA is used with multiple SHAs, +* so we have to allow all of them and not just one. */ if (!hash_algo) - n =snprintf (alg_name,CRYPTO_MAX_ALG_NAME , -"pkcs1pad(%s)" , - pkey->pkey_algo); -else - n =snprintf (alg_name,CRYPTO_MAX_ALG_NAME , -"pkcs1pad(%s,%s)" , - pkey->pkey_algo, hash_algo); -return n >=CRYPTO_MAX_ALG_NAME ? -EINVAL :0 ; - } - -if (strcmp (encoding,"raw" ) ==0 || -strcmp (encoding,"x962" ) ==0 ) { -strcpy (alg_name, pkey->pkey_algo); -return 0 ; +return -EINVAL ; +if (strcmp (hash_algo,"sha1" ) !=0 && +strcmp (hash_algo,"sha224" ) !=0 && +strcmp (hash_algo,"sha256" ) !=0 && +strcmp (hash_algo,"sha384" ) !=0 && +strcmp (hash_algo,"sha512" ) !=0 ) +return -EINVAL ; + }else if (strcmp (pkey->pkey_algo,"sm2" ) ==0 ) { +if (strcmp (encoding,"raw" ) !=0 ) +return -EINVAL ; +if (!hash_algo) +return -EINVAL ; +if (strcmp (hash_algo,"sm3" ) !=0 ) +return -EINVAL ; + }else if (strcmp (pkey->pkey_algo,"ecrdsa" ) ==0 ) { +if (strcmp (encoding,"raw" ) !=0 ) +return -EINVAL ; +if (!hash_algo) +return -EINVAL ; +if (strcmp (hash_algo,"streebog256" ) !=0 && +strcmp (hash_algo,"streebog512" ) !=0 ) +return -EINVAL ; + }else { +/* Unknown public key algorithm */ +return -ENOPKG ; } - -return -ENOPKG ; +if (strscpy (alg_name, pkey->pkey_algo,CRYPTO_MAX_ALG_NAME ) <0 ) +return -EINVAL ; +return 0 ; }static u8 *pkey_pack_u32 (u8 *dst,u32 val)
@@ -113,9 +157,8 @@ static int software_key_query(const struct kernel_pkey_params *params,u8 *key, *ptr;int ret, len; - ret =software_key_determine_akcipher (params->encoding, - params->hash_algo, - pkey, alg_name); + ret =software_key_determine_akcipher (pkey, params->encoding, + params->hash_algo, alg_name);if (ret <0 )return ret;
@@ -179,9 +222,8 @@ static int software_key_eds_op(struct kernel_pkey_params *params,pr_devel ("==>%s()\n" , __func__); - ret =software_key_determine_akcipher (params->encoding, - params->hash_algo, - pkey, alg_name); + ret =software_key_determine_akcipher (pkey, params->encoding, + params->hash_algo, alg_name);if (ret <0 )return ret;
@@ -340,9 +382,8 @@ int public_key_verify_signature(const struct public_key *pkey,return -EKEYREJECTED ; } - ret =software_key_determine_akcipher (sig->encoding, - sig->hash_algo, - pkey, alg_name); + ret =software_key_determine_akcipher (pkey, sig->encoding, + sig->hash_algo, alg_name);if (ret <0 )return ret;
Signature · 1 line
2.35.1
Re: [PATCH v2 2/2] KEYS: asymmetric: properly validate hash_algo and encoding
Quoted 18 lines · Eric Biggers
From: Eric Biggers <[email protected]>
It is insecure to allow arbitrary hash algorithms and signature encodings to be used with arbitrary signature algorithms. Notably, ECDSA, ECRDSA, and SM2 all sign/verify raw hash values and don't disambiguate between different hash algorithms like RSA PKCS#1 v1.5 padding does. Therefore, they need to be restricted to certain sets of hash algorithms (ideally just one, but in practice small sets are used). Additionally, the encoding is an integral part of modern signature algorithms, and is not supposed to vary.
Therefore, tighten the checks of
hash_algoand encoding done bysoftware_key_determine_akcipher().Also rearrange the parameters to
software_key_determine_akcipher()to put thepublic_keyfirst, as this is the most important parameter and it often determines everything else.
Quoted 7 lines
Fixes 299f561a6693 ("x509: Add support for parsing x509 certs with ECDSA keys")Fixes 215525639631 ("X.509: support OSCCA SM2-with-SM3 certificate verification")Fixes 0d7a78643f69 ("crypto: ecrdsa - add EC-RDSA (GOST 34.10) algorithm")Tested-by Stefan Berger <[email protected]>Tested-by Tianjia Zhang <[email protected]>Signed-off-by Eric Biggers <[email protected]>
Small question below.
Quoted 43 lines
--- crypto/asymmetric_keys/public_key.c | 111 +++++++++++++++++++--------- 1 file changed, 76 insertions(+), 35 deletions(-)crypto/asymmetric_keys/public_key.c +17
-10@@ -60,39 +60,83 @@ static void public_key_destroy(void *payload0, void *payload3) }/* -* Determine the crypto algorithm name. +* Given a public_key, and an encoding and hash_algo to be used for signing +* and/or verification with that key, determine the name of the corresponding +* akcipher algorithm. Also check that encoding and hash_algo are allowed. */ -static -int software_key_determine_akcipher (const char *encoding, -const char *hash_algo, -const struct public_key *pkey, -char alg_name[CRYPTO_MAX_ALG_NAME ]) +static int +software_key_determine_akcipher (const struct public_key *pkey, +const char *encoding,const char *hash_algo, +char alg_name[CRYPTO_MAX_ALG_NAME ]) {int n; -if (strcmp (encoding,"pkcs1" ) ==0 ) { -/* The data wangled by the RSA algorithm is typically padded -* and encoded in some manner, such as EMSA-PKCS1-1_5 [RFC3447 -* sec 8.2]. +if (!encoding) +return -EINVAL ; + +if (strcmp (pkey->pkey_algo,"rsa" ) ==0 ) { +/* +* RSA signatures usually use EMSA-PKCS1-1_5 [RFC3447 sec 8.2]. +*/ +if (strcmp (encoding,"pkcs1" ) ==0 ) { +if (!hash_algo) + n = snprintf(alg_name, CRYPTO_MAX_ALG_NAME,
crypto/asymmetric_keys/public_key.c static void public_key_destroy(void *payload0, void *payload3) · line 93
Quoted 10 lines
crypto/asymmetric_keys/public_key.c +10
-0+"pkcs1pad(%s)" , + pkey->pkey_algo); + else + n =snprintf (alg_name,CRYPTO_MAX_ALG_NAME , +"pkcs1pad(%s,%s)" , + pkey->pkey_algo, hash_algo); +return n >=CRYPTO_MAX_ALG_NAME ? -EINVAL :0 ; + } +if (strcmp (encoding,"raw" ) !=0 ) +return -EINVAL ;
Should raw RSA be allowed at all? I understand it was there before, but I wonder what is the use case.
Thanks,
Quoted 103 lines
crypto/asymmetric_keys/public_key.c +49
-25+/* +* Raw RSA cannot differentiate between different hash +* algorithms. +*/ +if (hash_algo) +return -EINVAL ; + }else if (strncmp (pkey->pkey_algo,"ecdsa" ,5 ) ==0 ) { +if (strcmp (encoding,"x962" ) !=0 ) +return -EINVAL ; +/* +* ECDSA signatures are taken over a raw hash, so they don't +* differentiate between different hash algorithms. That means +* that the verifier should hard-code a specific hash algorithm. +* Unfortunately, in practice ECDSA is used with multiple SHAs, +* so we have to allow all of them and not just one. */ if (!hash_algo) - n =snprintf (alg_name,CRYPTO_MAX_ALG_NAME , -"pkcs1pad(%s)" , - pkey->pkey_algo); -else - n =snprintf (alg_name,CRYPTO_MAX_ALG_NAME , -"pkcs1pad(%s,%s)" , - pkey->pkey_algo, hash_algo); -return n >=CRYPTO_MAX_ALG_NAME ? -EINVAL :0 ; - } - -if (strcmp (encoding,"raw" ) ==0 || -strcmp (encoding,"x962" ) ==0 ) { -strcpy (alg_name, pkey->pkey_algo); -return 0 ; +return -EINVAL ; +if (strcmp (hash_algo,"sha1" ) !=0 && +strcmp (hash_algo,"sha224" ) !=0 && +strcmp (hash_algo,"sha256" ) !=0 && +strcmp (hash_algo,"sha384" ) !=0 && +strcmp (hash_algo,"sha512" ) !=0 ) +return -EINVAL ; + }else if (strcmp (pkey->pkey_algo,"sm2" ) ==0 ) { +if (strcmp (encoding,"raw" ) !=0 ) +return -EINVAL ; +if (!hash_algo) +return -EINVAL ; +if (strcmp (hash_algo,"sm3" ) !=0 ) +return -EINVAL ; + }else if (strcmp (pkey->pkey_algo,"ecrdsa" ) ==0 ) { +if (strcmp (encoding,"raw" ) !=0 ) +return -EINVAL ; +if (!hash_algo) +return -EINVAL ; +if (strcmp (hash_algo,"streebog256" ) !=0 && +strcmp (hash_algo,"streebog512" ) !=0 ) +return -EINVAL ; + }else { +/* Unknown public key algorithm */ +return -ENOPKG ; } - -return -ENOPKG ; +if (strscpy (alg_name, pkey->pkey_algo,CRYPTO_MAX_ALG_NAME ) <0 ) +return -EINVAL ; +return 0 ; }static u8 *pkey_pack_u32 (u8 *dst,u32 val)@@ -113,9 +157,8 @@ static int software_key_query(const struct kernel_pkey_params *params,u8 *key, *ptr;int ret, len; - ret =software_key_determine_akcipher (params->encoding, - params->hash_algo, - pkey, alg_name); + ret =software_key_determine_akcipher (pkey, params->encoding, + params->hash_algo, alg_name);if (ret <0 )return ret;@@ -179,9 +222,8 @@ static int software_key_eds_op(struct kernel_pkey_params *params,pr_devel ("==>%s()\n" , __func__); - ret =software_key_determine_akcipher (params->encoding, - params->hash_algo, - pkey, alg_name); + ret =software_key_determine_akcipher (pkey, params->encoding, + params->hash_algo, alg_name);if (ret <0 )return ret;@@ -340,9 +382,8 @@ int public_key_verify_signature(const struct public_key *pkey,return -EKEYREJECTED ; } - ret =software_key_determine_akcipher (sig->encoding, - sig->hash_algo, - pkey, alg_name); + ret =software_key_determine_akcipher (pkey, sig->encoding, + sig->hash_algo, alg_name);if (ret <0 )return ret;Signature · 1 line
2.35.1
PATCH v2 1/1 KEYS: asymmetric: enforce SM2 signature use pkey algo
In reply to Eric BiggersThe signature verification of SM2 needs to add the Za value and recalculate sig->digest, which requires the detection of the pkey_algo in public_key_verify_signature(). As Eric Biggers said, the pkey_algo field in sig is attacker-controlled and should be use pkey->pkey_algo instead of sig->pkey_algo, and secondly, if sig->pkey_algo is NULL, it will also cause signature verification failure.
The software_key_determine_akcipher() already forces the algorithms are matched, so the SM3 algorithm is enforced in the SM2 signature, although this has been checked, we still avoid using any algorithm information in the signature as input.
---
v2:
- add Fixes tag to commit message
crypto/asymmetric_keys/public_key.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
crypto/asymmetric_keys/public_key.c +3 -3
@@ -309,7 +309,8 @@ static int cert_sig_digest_update(const struct public_key_signature *sig,if (ret)return ret; - tfm =crypto_alloc_shash (sig->hash_algo,0 ,0 ); +/* SM2 signatures always use the SM3 hash algorithm */ + tfm =crypto_alloc_shash ("sm3" ,0 ,0 );if (IS_ERR (tfm))return PTR_ERR (tfm);
@@ -414,8 +415,7 @@ int public_key_verify_signature(const struct public_key *pkey,if (ret) goto error_free_key; -if (sig->pkey_algo &&strcmp (sig->pkey_algo,"sm2" ) ==0 && - sig->data_size) { +if (strcmp (pkey->pkey_algo,"sm2" ) ==0 && sig->data_size) { ret =cert_sig_digest_update (sig, tfm);if (ret) goto error_free_key;
Signature · 1 line
2.34.1