[PATCH v2 1/5] crypto: rsa-pkcs1pad - only allow with rsa

[PATCH v2 1/5] crypto: rsa-pkcs1pad - only allow with rsa

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

The pkcs1pad template can be instantiated with an arbitrary akcipher
algorithm, which doesn't make sense; it is specifically an RSA padding
scheme.  Make it check that the underlying algorithm really is RSA.

Fixes: 3d5b1ecdea6f ("crypto: rsa - RSA padding algorithm")
Cc: <stable@vger.kernel.org> # v4.5+
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 crypto/rsa-pkcs1pad.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/crypto/rsa-pkcs1pad.c b/crypto/rsa-pkcs1pad.c
index 8ac3e73e8ea65..1b35457814258 100644
--- a/crypto/rsa-pkcs1pad.c
+++ b/crypto/rsa-pkcs1pad.c
@@ -621,6 +621,11 @@ static int pkcs1pad_create(struct crypto_template *tmpl, struct rtattr **tb)
 
 	rsa_alg = crypto_spawn_akcipher_alg(&ctx->spawn);
 
+	if (strcmp(rsa_alg->base.cra_name, "rsa") != 0) {
+		err = -EINVAL;
+		goto err_free_inst;
+	}
+
 	err = -ENAMETOOLONG;
 	hash_name = crypto_attr_alg_name(tb[2]);
 	if (IS_ERR(hash_name)) {
-- 
2.34.1

[PATCH v2 2/5] crypto: rsa-pkcs1pad - correctly get hash from source scatterlist

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

Commit c7381b012872 ("crypto: akcipher - new verify API for public key
algorithms") changed akcipher_alg::verify to take in both the signature
and the actual hash and do the signature verification, rather than just
return the hash expected by the signature as was the case before.  To do
this, it implemented a hack where the signature and hash are
concatenated with each other in one scatterlist.

Obviously, for this to work correctly, akcipher_alg::verify needs to
correctly extract the two items from the scatterlist it is given.
Unfortunately, it doesn't correctly extract the hash in the case where
the signature is longer than the RSA key size, as it assumes that the
signature's length is equal to the RSA key size.  This causes a prefix
of the hash, or even the entire hash, to be taken from the *signature*.

(Note, the case of a signature longer than the RSA key size should not
be allowed in the first place; a separate patch will fix that.)

It is unclear whether the resulting scheme has any useful security
properties.

Fix this by correctly extracting the hash from the scatterlist.

Fixes: c7381b012872 ("crypto: akcipher - new verify API for public key algorithms")
Cc: <stable@vger.kernel.org> # v5.2+
Reviewed-by: Vitaly Chikunov <vt@altlinux.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 crypto/rsa-pkcs1pad.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crypto/rsa-pkcs1pad.c b/crypto/rsa-pkcs1pad.c
index 1b35457814258..7b223adebabf6 100644
--- a/crypto/rsa-pkcs1pad.c
+++ b/crypto/rsa-pkcs1pad.c
@@ -495,7 +495,7 @@ static int pkcs1pad_verify_complete(struct akcipher_request *req, int err)
 			   sg_nents_for_len(req->src,
 					    req->src_len + req->dst_len),
 			   req_ctx->out_buf + ctx->key_size,
-			   req->dst_len, ctx->key_size);
+			   req->dst_len, req->src_len);
 	/* Do the actual verification step. */
 	if (memcmp(req_ctx->out_buf + ctx->key_size, out_buf + pos,
 		   req->dst_len) != 0)
-- 
2.34.1

[PATCH v2 3/5] crypto: rsa-pkcs1pad - restore signature length check

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

RSA PKCS#1 v1.5 signatures are required to be the same length as the RSA
key size.  RFC8017 specifically requires the verifier to check this
(https://datatracker.ietf.org/doc/html/rfc8017#section-8.2.2).

Commit a49de377e051 ("crypto: Add hash param to pkcs1pad") changed the
kernel to allow longer signatures, but didn't explain this part of the
change; it seems to be unrelated to the rest of the commit.

Revert this change, since it doesn't appear to be correct.

We can be pretty sure that no one is relying on overly-long signatures
(which would have to be front-padded with zeroes) being supported, given
that they would have been broken since commit c7381b012872
("crypto: akcipher - new verify API for public key algorithms").

Fixes: a49de377e051 ("crypto: Add hash param to pkcs1pad")
Cc: <stable@vger.kernel.org> # v4.6+
Cc: Tadeusz Struk <tadeusz.struk@linaro.org>
Suggested-by: Vitaly Chikunov <vt@altlinux.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 crypto/rsa-pkcs1pad.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crypto/rsa-pkcs1pad.c b/crypto/rsa-pkcs1pad.c
index 7b223adebabf6..6b556ddeb3a00 100644
--- a/crypto/rsa-pkcs1pad.c
+++ b/crypto/rsa-pkcs1pad.c
@@ -538,7 +538,7 @@ static int pkcs1pad_verify(struct akcipher_request *req)
 
 	if (WARN_ON(req->dst) ||
 	    WARN_ON(!req->dst_len) ||
-	    !ctx->key_size || req->src_len < ctx->key_size)
+	    !ctx->key_size || req->src_len != ctx->key_size)
 		return -EINVAL;
 
 	req_ctx->out_buf = kmalloc(ctx->key_size + req->dst_len, GFP_KERNEL);
-- 
2.34.1

[PATCH v2 4/5] crypto: rsa-pkcs1pad - fix buffer overread in pkcs1pad_verify_complete()

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

Before checking whether the expected digest_info is present, we need to
check that there are enough bytes remaining.

Fixes: a49de377e051 ("crypto: Add hash param to pkcs1pad")
Cc: <stable@vger.kernel.org> # v4.6+
Cc: Tadeusz Struk <tadeusz.struk@linaro.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 crypto/rsa-pkcs1pad.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/crypto/rsa-pkcs1pad.c b/crypto/rsa-pkcs1pad.c
index 6b556ddeb3a00..9d804831c8b3f 100644
--- a/crypto/rsa-pkcs1pad.c
+++ b/crypto/rsa-pkcs1pad.c
@@ -476,6 +476,8 @@ static int pkcs1pad_verify_complete(struct akcipher_request *req, int err)
 	pos++;
 
 	if (digest_info) {
+		if (digest_info->size > dst_len - pos)
+			goto done;
 		if (crypto_memneq(out_buf + pos, digest_info->data,
 				  digest_info->size))
 			goto done;
-- 
2.34.1