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SubjectRe: [RFC PATCH] tee: add support for application-based session login methods
On Mon, 28 Sep 2020 15:43:47 +0200
Jens Wiklander <jens.wiklander@linaro.org> wrote:

> Hi Elvira,
>
> On Thu, Sep 17, 2020 at 06:38:03PM +0300, Elvira Khabirova wrote:
> > GP TEE Client API in addition to login methods already supported
> > in the kernel also defines several application-based methods:
> > TEEC_LOGIN_APPLICATION, TEEC_LOGIN_USER_APPLICATION, and
> > TEEC_LOGIN_GROUP_APPLICATION.
> >
> > It specifies credentials generated for TEEC_LOGIN_APPLICATION as only
> > depending on the identity of the program, being persistent within one
> > implementation, across multiple invocations of the application
> > and across power cycles, enabling them to be used to disambiguate
> > persistent storage. The exact nature is REE-specific.
> >
> > As the exact method of generating application identifier strings may
> > vary between vendors, setups and installations, add two suggested
> > methods and an exact framework for vendors to extend upon.
> >
> > Signed-off-by: Elvira Khabirova <e.khabirova@omprussia.ru>
> > ---
> > drivers/tee/Kconfig | 29 +++++++++
> > drivers/tee/tee_core.c | 136 ++++++++++++++++++++++++++++++++++++++++-
> > 2 files changed, 164 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/tee/Kconfig b/drivers/tee/Kconfig
> > index e99d840c2511..4cd6e0d2aad5 100644
> > --- a/drivers/tee/Kconfig
> > +++ b/drivers/tee/Kconfig
> > @@ -11,6 +11,35 @@ config TEE
> > This implements a generic interface towards a Trusted Execution
> > Environment (TEE).
> >
> > +choice
> > + prompt "Application ID for client UUID"
> > + depends on TEE
> > + default TEE_APPID_PATH
> > + help
> > + This option allows to choose which method will be used to generate
> > + application identifiers for client UUID generation when login methods
> > + TEE_LOGIN_APPLICATION, TEE_LOGIN_USER_APPLICATION
> > + and TEE_LOGIN_GROUP_APPLICATION are used.
> > + Please be mindful of the security of each method in your particular
> > + installation.
> > +
> > + config TEE_APPID_PATH
> > + bool "Path-based application ID"
> > + help
> > + Use the executable's path as an application ID.
> > +
> > + config TEE_APPID_SECURITY
> > + bool "Security extended attribute based application ID"
> > + help
> > + Use the executable's security extended attribute as an application ID.
> > +endchoice
> > +
> > +config TEE_APPID_SECURITY_XATTR
> > + string "Security extended attribute to use for application ID"
> > + depends on TEE_APPID_SECURITY
> > + help
> > + Attribute to be used as an application ID (with the security prefix removed).
> > +
> > if TEE
> >
> > menu "TEE drivers"
> > diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c
> > index 64637e09a095..19c965dd212b 100644
> > --- a/drivers/tee/tee_core.c
> > +++ b/drivers/tee/tee_core.c
> > @@ -7,8 +7,10 @@
> >
> > #include <linux/cdev.h>
> > #include <linux/cred.h>
> > +#include <linux/file.h>
> > #include <linux/fs.h>
> > #include <linux/idr.h>
> > +#include <linux/mm.h>
> > #include <linux/module.h>
> > #include <linux/slab.h>
> > #include <linux/tee_drv.h>
> > @@ -17,11 +19,15 @@
> > #include <crypto/sha.h>
> > #include "tee_private.h"
> >
> > +#ifdef CONFIG_TEE_APPID_SECURITY
> No need for the ifdef, just inlude the file unconditionally above.
>
> > +#include <linux/security.h>
> > +#endif
> > +
> > #define TEE_NUM_DEVICES 32
> >
> > #define TEE_IOCTL_PARAM_SIZE(x) (sizeof(struct tee_param) * (x))
> >
> > -#define TEE_UUID_NS_NAME_SIZE 128
> > +#define TEE_UUID_NS_NAME_SIZE PATH_MAX
> >
> > /*
> > * TEE Client UUID name space identifier (UUIDv4)
> > @@ -125,6 +131,67 @@ static int tee_release(struct inode *inode, struct file *filp)
> > return 0;
> > }
> >
> > +#ifdef CONFIG_TEE_APPID_SECURITY
> > +static const char *tee_session_get_application_id(void **data)
> static char *get_app_id(void) should be enough.
>
> > +{
> > + struct file *exe_file;
> > + const char *name = CONFIG_TEE_APPID_SECURITY_XATTR;
> > + int len;
> > +
> > + exe_file = get_mm_exe_file(current->mm);
> > + if (!exe_file)
> > + return ERR_PTR(-ENOENT);
> > +
> > + if (!exe_file->f_inode) {
> > + fput(exe_file);
> > + return ERR_PTR(-ENOENT);
> > + }
> > +
>
> You could perhaps add a comment here on the expected properties of this
> data. Something along (don't know if I'm even close) "string
> representation of the the hash of the binary and time stamp".
>
> > + len = security_inode_getsecurity(exe_file->f_inode, name, data, true);
> > + if (len < 0)
> > + return ERR_PTR(len);
> > +
> > + fput(exe_file);
> > +
> > + return *data;
> > +}
> > +#endif /* CONFIG_TEE_APPID_SECURITY */
> > +
> > +#ifdef CONFIG_TEE_APPID_PATH
> > +static const char *tee_session_get_application_id(void **data)
> > +{
> > + struct file *exe_file;
> > + char *path;
> > +
> > + *data = kzalloc(TEE_UUID_NS_NAME_SIZE, GFP_KERNEL);
> > + if (!*data)
> > + return ERR_PTR(-ENOMEM);
> > +
> > + exe_file = get_mm_exe_file(current->mm);
> > + if (!exe_file) {
> > + kfree(*data);
> > + return ERR_PTR(-ENOENT);
> > + }
> > +
> > + path = file_path(exe_file, *data, TEE_UUID_NS_NAME_SIZE);
> > + if (IS_ERR(path)) {
> > + kfree(*data);
> > + return path;
> > + }
> > +
> > + fput(exe_file);
> > +
> > + return path;
> > +}
> > +#endif /* CONFIG_TEE_APPID_PATH */
> > +
> > +#if defined(CONFIG_TEE_APPID_PATH) || defined(CONFIG_TEE_APPID_SECURITY)
> > +static void tee_session_free_application_id(void *data)
> > +{
> > + kfree(data);
> > +}
> This function isn't needed, we can call kfree() directly.
>
> > +#endif /* CONFIG_TEE_APPID_PATH || CONFIG_TEE_APPID_SECURITY */
> > +
> > /**
> > * uuid_v5() - Calculate UUIDv5
> > * @uuid: Resulting UUID
> > @@ -197,6 +264,8 @@ int tee_session_calc_client_uuid(uuid_t *uuid, u32 connection_method,
> > gid_t ns_grp = (gid_t)-1;
> > kgid_t grp = INVALID_GID;
> > char *name = NULL;
> > + void *application_id_data = NULL;
> This isn't needed
The only reason application_id_data exists (and get_application_id has a parameter)
is because when defined(CONFIG_TEE_APPID_PATH), file_path() returns a pointer
that often starts at an offset into the buffer (see the comment above d_path()).
Therefore we end up with a buffer that's not equal to application_id which we
want to free later. The other way (other than having a void **data parameter)
would be to allocate a new buffer, copy the resulting path there, and return
the new buffer instead of the one used by file_path().
Let me know which solution is preferred.

> > + const char *application_id = NULL;
> char *app_id = NULL;
>
> > int name_len;
> > int rc;
> >
> > @@ -217,6 +286,14 @@ int tee_session_calc_client_uuid(uuid_t *uuid, u32 connection_method,
> > * For TEEC_LOGIN_GROUP:
> > * gid=<gid>
> > *
> > + * For TEEC_LOGIN_APPLICATION:
> > + * app=<application id>
> > + *
> > + * For TEEC_LOGIN_USER_APPLICATION:
> > + * uid=<uid>:app=<application id>
> > + *
> > + * For TEEC_LOGIN_GROUP_APPLICATION:
> > + * gid=<gid>:app=<application id>
> > */
> >
> > name = kzalloc(TEE_UUID_NS_NAME_SIZE, GFP_KERNEL);
> > @@ -249,6 +326,63 @@ int tee_session_calc_client_uuid(uuid_t *uuid, u32 connection_method,
> > }
> > break;
> >
> > + case TEE_IOCTL_LOGIN_APPLICATION:
> > + application_id = tee_session_get_application_id(&application_id_data);
> > + if (IS_ERR(application_id)) {
> > + rc = PTR_ERR(application_id);
> > + goto out_free_name;
> > + }
> > +
> > + name_len = snprintf(name, TEE_UUID_NS_NAME_SIZE, "app=%s",
> > + application_id);
> > + tee_session_free_application_id(application_id_data);
> > +
> > + if (name_len >= TEE_UUID_NS_NAME_SIZE) {
> > + rc = -E2BIG;
> > + goto out_free_name;
> > + }
> It looks like we remove these tests and replace them with
> if (name_len < TEE_UUID_NS_NAME_SIZE)
> rc = uuid_v5(uuid, &tee_client_uuid_ns, name, name_len);
> else
> rc = -E2BIG
>
> below, just above the "out_free_name:" label.
>
> This function is small and simple enough that it should be easy to see
> what's going on any way.
>
> Thanks,
> Jens
>
> > + break;
> > +
> > + case TEE_IOCTL_LOGIN_USER_APPLICATION:
> > + application_id = tee_session_get_application_id(&application_id_data);
> > + if (IS_ERR(application_id)) {
> > + rc = PTR_ERR(application_id);
> > + goto out_free_name;
> > + }
> > +
> > + name_len = snprintf(name, TEE_UUID_NS_NAME_SIZE, "uid=%x:app=%s",
> > + current_euid().val, application_id);
> > + tee_session_free_application_id(application_id_data);
> > +
> > + if (name_len >= TEE_UUID_NS_NAME_SIZE) {
> > + rc = -E2BIG;
> > + goto out_free_name;
> > + }
> > + break;
> > +
> > + case TEE_IOCTL_LOGIN_GROUP_APPLICATION:
> > + memcpy(&ns_grp, connection_data, sizeof(gid_t));
> > + grp = make_kgid(current_user_ns(), ns_grp);
> > + if (!gid_valid(grp) || !in_egroup_p(grp)) {
> > + rc = -EPERM;
> > + goto out_free_name;
> > + }
> > +
> > + application_id = tee_session_get_application_id(&application_id_data);
> > + if (IS_ERR(application_id)) {
> > + rc = PTR_ERR(application_id);
> > + goto out_free_name;
> > + }
> > + name_len = snprintf(name, TEE_UUID_NS_NAME_SIZE, "gid=%x:app=%s",
> > + grp.val, application_id);
> > + tee_session_free_application_id(application_id_data);
> > +
> > + if (name_len >= TEE_UUID_NS_NAME_SIZE) {
> > + rc = -E2BIG;
> > + goto out_free_name;
> > + }
> > + break;
> > +
> > default:
> > rc = -EINVAL;
> > goto out_free_name;
> > --
> > 2.28.0
> >

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