From 6a21fe5a89dd5d8fcefc53aad75cc68f1dfcb3cb Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Tue, 18 Jan 2022 16:13:03 -0800 Subject: crypto: rsa-pkcs1pad - correctly get hash from source scatterlist Commit 5bb3d56f3518 ("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: 5bb3d56f3518 ("crypto: akcipher - new verify API for public key algorithms") Cc: # v5.2+ Reviewed-by: Vitaly Chikunov Signed-off-by: Eric Biggers Signed-off-by: Herbert Xu --- 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 1b354578..7b223ade 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) -- cgit v1.2.3