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evp_md: assert digest is provided for algctx reuse

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When reusing an algctx (it was always freed on reinitialization,
prior to #18105), assert that the associated digest is provided.
We implicitly rely on this for algctx reuse to be safe (since
an implicit fetch could potentially change the digest object used,
including provider, which accordingly could change the layout of the
algctx object.

From code inspection, this is currently always the case -- the only
way to set an algctx requires the provider to be set, and the only
ways to change or remove a provider without destroying the entier
EVP_MD_CTX will also free the algctx.  Adding an assertion will help
ensure that this remains true as the code evolves.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/18224)
This commit is contained in:
Benjamin Kaduk 2022-05-02 10:40:57 -07:00 committed by Benjamin Kaduk
parent b807c2fbab
commit 221d65ba53
1 changed files with 9 additions and 2 deletions
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11
crypto/evp/digest.c
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@ -245,8 +245,15 @@ static int evp_md_init_internal(EVP_MD_CTX *ctx, const EVP_MD *type,
cleanup_old_md_data(ctx, 1);
/* Start of non-legacy code below */
if (ctx->digest != type && !evp_md_ctx_free_algctx(ctx))
return 0;
if (ctx->digest == type) {
if (!ossl_assert(type->prov != NULL)) {
ERR_raise(ERR_LIB_EVP, EVP_R_INITIALIZATION_ERROR);
return 0;
}
} else {
if (!evp_md_ctx_free_algctx(ctx))
return 0;
}
if (type->prov == NULL) {
#ifdef FIPS_MODULE