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

Message ID 20220119001306.85355-4-ebiggers@kernel.org
State New
Headers show
Series [v2,1/5] crypto: rsa-pkcs1pad - only allow with rsa | expand

Commit Message

Eric Biggers Jan. 19, 2022, 12:13 a.m. UTC 
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(-)
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Patch

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);