From: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
To: David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: keyrings-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Matthew Garrett
<matthew.garrett-05XSO3Yj/JvQT0dZR+AlfA@public.gmane.org>,
"linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
linux-security-module
<linux-security-module-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Josh Boyer
<jwboyer-rxtnV0ftBwyoClj4AeEUq9i2O/JbrIOy@public.gmane.org>
Subject: Re: [PATCH 9/9] MODSIGN: Allow the "db" UEFI variable to be suppressed
Date: Mon, 21 Nov 2016 16:18:56 +0000 [thread overview]
Message-ID: <CAKv+Gu96ihE7pHrCCeCpy78man-r821b3Vs4Tn_RsYyzY4HV2Q@mail.gmail.com> (raw)
In-Reply-To: <147931990959.16460.3038875071067540418.stgit-S6HVgzuS8uM4Awkfq6JHfwNdhmdF6hFW@public.gmane.org>
On 16 November 2016 at 18:11, David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
> From: Josh Boyer <jwboyer-rxtnV0ftBwyoClj4AeEUq9i2O/JbrIOy@public.gmane.org>
>
> If a user tells shim to not use the certs/hashes in the UEFI db variable
> for verification purposes, shim will set a UEFI variable called
> MokIgnoreDB. Have the uefi import code look for this and ignore the db
> variable if it is found.
>
Similar concern as in the previous patch: it appears to me that you
can DoS a machine by setting MokIgnoreDB if, e.g., its modules are
signed against a cert that resides in db, and shim/mokmanager are not
being used.
> Signed-off-by: Josh Boyer <jwboyer-rxtnV0ftBwyoClj4AeEUq9i2O/JbrIOy@public.gmane.org>
> Signed-off-by: David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> ---
>
> certs/load_uefi.c | 44 ++++++++++++++++++++++++++++++++++----------
> 1 file changed, 34 insertions(+), 10 deletions(-)
>
> diff --git a/certs/load_uefi.c b/certs/load_uefi.c
> index b44e464c3ff4..3d8845986019 100644
> --- a/certs/load_uefi.c
> +++ b/certs/load_uefi.c
> @@ -13,6 +13,26 @@ static __initdata efi_guid_t efi_cert_x509_sha256_guid = EFI_CERT_X509_SHA256_GU
> static __initdata efi_guid_t efi_cert_sha256_guid = EFI_CERT_SHA256_GUID;
>
> /*
> + * Look to see if a UEFI variable called MokIgnoreDB exists and return true if
> + * it does.
> + *
> + * This UEFI variable is set by the shim if a user tells the shim to not use
> + * the certs/hashes in the UEFI db variable for verification purposes. If it
> + * is set, we should ignore the db variable also and the true return indicates
> + * this.
> + */
> +static __init bool uefi_check_ignore_db(void)
> +{
> + efi_status_t status;
> + unsigned int db = 0;
> + unsigned long size = sizeof(db);
> + efi_guid_t guid = EFI_SHIM_LOCK_GUID;
> +
> + status = efi.get_variable(L"MokIgnoreDB", &guid, NULL, &size, &db);
> + return status == EFI_SUCCESS;
> +}
> +
> +/*
> * Get a certificate list blob from the named EFI variable.
> */
> static __init void *get_cert_list(efi_char16_t *name, efi_guid_t *guid,
> @@ -113,7 +133,9 @@ static __init efi_element_handler_t get_handler_for_dbx(const efi_guid_t *sig_ty
> }
>
> /*
> - * Load the certs contained in the UEFI databases
> + * Load the certs contained in the UEFI databases into the secondary trusted
> + * keyring and the UEFI blacklisted X.509 cert SHA256 hashes into the blacklist
> + * keyring.
> */
> static int __init load_uefi_certs(void)
> {
> @@ -129,15 +151,17 @@ static int __init load_uefi_certs(void)
> /* Get db, MokListRT, and dbx. They might not exist, so it isn't
> * an error if we can't get them.
> */
> - db = get_cert_list(L"db", &secure_var, &dbsize);
> - if (!db) {
> - pr_err("MODSIGN: Couldn't get UEFI db list\n");
> - } else {
> - rc = parse_efi_signature_list("UEFI:db",
> - db, dbsize, get_handler_for_db);
> - if (rc)
> - pr_err("Couldn't parse db signatures: %d\n", rc);
> - kfree(db);
> + if (!uefi_check_ignore_db()) {
> + db = get_cert_list(L"db", &secure_var, &dbsize);
> + if (!db) {
> + pr_err("MODSIGN: Couldn't get UEFI db list\n");
> + } else {
> + rc = parse_efi_signature_list("UEFI:db",
> + db, dbsize, get_handler_for_db);
> + if (rc)
> + pr_err("Couldn't parse db signatures: %d\n", rc);
> + kfree(db);
> + }
> }
>
> mok = get_cert_list(L"MokListRT", &mok_var, &moksize);
>
> --
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next prev parent reply other threads:[~2016-11-21 16:18 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-16 18:10 [PATCH 0/9] KEYS: Blacklisting & UEFI database load David Howells
2016-11-16 18:10 ` [PATCH 1/9] KEYS: Add a system blacklist keyring David Howells
2016-11-16 18:10 ` [PATCH 2/9] X.509: Allow X.509 certs to be blacklisted David Howells
2016-11-16 18:11 ` [PATCH 3/9] PKCS#7: Handle blacklisted certificates David Howells
2016-11-16 18:11 ` [PATCH 4/9] KEYS: Allow unrestricted boot-time addition of keys to secondary keyring David Howells
2016-11-17 6:41 ` Petko Manolov
2016-11-17 9:56 ` David Howells
2016-11-17 11:18 ` David Howells
[not found] ` <26349.1479376560-S6HVgzuS8uM4Awkfq6JHfwNdhmdF6hFW@public.gmane.org>
2016-11-17 10:22 ` Petko Manolov
2016-11-21 14:04 ` Mimi Zohar
2016-11-21 15:17 ` David Howells
2016-11-21 16:24 ` Mimi Zohar
2016-11-16 18:11 ` [PATCH 5/9] efi: Add SHIM and image security database GUID definitions David Howells
2016-11-21 16:07 ` Ard Biesheuvel
2016-11-16 18:11 ` [PATCH 6/9] efi: Add EFI signature data types David Howells
2016-11-16 23:43 ` Mat Martineau
[not found] ` <alpine.OSX.2.20.1611161535590.67352-zaFMaa3cLiZe6KzckbbZvYT4S9po1h25@public.gmane.org>
2016-11-17 9:44 ` David Howells
[not found] ` <26198.1479375840-S6HVgzuS8uM4Awkfq6JHfwNdhmdF6hFW@public.gmane.org>
2016-11-21 16:08 ` Ard Biesheuvel
2016-11-16 18:11 ` [PATCH 7/9] efi: Add an EFI signature blob parser David Howells
2016-11-16 18:11 ` [PATCH 8/9] MODSIGN: Import certificates from UEFI Secure Boot David Howells
2016-11-21 16:16 ` Ard Biesheuvel
[not found] ` <CAKv+Gu_QVyd1Jx7ZdnBzYmZzUnH4ZuhQgiGO-zx-JPViWosjXQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-11-21 16:25 ` Josh Boyer
[not found] ` <CA+5PVA6dWw-p3q9SBmJwQvuru4k7JZAraRZeb2=VDf8E=c=SmA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-11-24 19:22 ` James Bottomley
2016-11-24 19:17 ` James Bottomley
2016-12-02 18:57 ` James Bottomley
2016-12-02 20:18 ` Mimi Zohar
2016-11-16 18:11 ` [PATCH 9/9] MODSIGN: Allow the "db" UEFI variable to be suppressed David Howells
[not found] ` <147931990959.16460.3038875071067540418.stgit-S6HVgzuS8uM4Awkfq6JHfwNdhmdF6hFW@public.gmane.org>
2016-11-21 16:18 ` Ard Biesheuvel [this message]
[not found] ` <CAKv+Gu96ihE7pHrCCeCpy78man-r821b3Vs4Tn_RsYyzY4HV2Q-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-11-21 16:26 ` Josh Boyer
[not found] ` <CA+5PVA7SivAegwxdxuiAFL41Apie4JLK5KbtGGHLr1fP0p3MsQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-11-21 16:42 ` Ard Biesheuvel
[not found] ` <CAKv+Gu__wAnOawWZWVF6NF3En0suuFTBrFwwZ5KosqBU8LVHMA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-11-21 19:05 ` Peter Jones
2016-11-21 19:06 ` Ard Biesheuvel
2016-11-21 19:18 ` Peter Jones
2016-11-21 19:33 ` Ard Biesheuvel
2018-03-06 14:05 ` [PATCH 0/9] KEYS: Blacklisting & UEFI database load Jiri Slaby
2018-03-07 13:18 ` Mimi Zohar
2018-03-07 15:28 ` James Bottomley
2018-03-11 3:20 ` joeyli
2018-03-19 14:12 ` Mimi Zohar
2018-03-27 11:08 ` joeyli
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