On Wed, Oct 6, 2021 at 8:46 PM Todd Kjos <tkjos@xxxxxxxxxx> wrote:
>
> Use the 'struct cred' saved at binder_open() to lookup
> the security ID via security_cred_getsecid(). This
> ensures that the security context that opened binder
> is the one used to generate the secctx.
>
> Fixes: ec74136ded79 ("binder: create node flag to request sender's
> security context")
> Signed-off-by: Todd Kjos <tkjos@xxxxxxxxxx>
> Suggested-by: Stephen Smalley <stephen.smalley.work@xxxxxxxxx>
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # 5.4+
> ---
> v3: added this patch to series
> v4: fix build-break for !CONFIG_SECURITY
>
> drivers/android/binder.c | 11 +----------
> include/linux/security.h | 4 ++++
> 2 files changed, 5 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index ca599ebdea4a..989afd0804ca 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -2722,16 +2722,7 @@ static void binder_transaction(struct binder_proc *proc,
> u32 secid;
> size_t added_size;
>
> - /*
> - * Arguably this should be the task's subjective LSM secid but
> - * we can't reliably access the subjective creds of a task
> - * other than our own so we must use the objective creds, which
> - * are safe to access. The downside is that if a task is
> - * temporarily overriding it's creds it will not be reflected
> - * here; however, it isn't clear that binder would handle that
> - * case well anyway.
> - */
> - security_task_getsecid_obj(proc->tsk, &secid);
> + security_cred_getsecid(proc->cred, &secid);
> ret = security_secid_to_secctx(secid, &secctx, &secctx_sz);
> if (ret) {
> return_error = BR_FAILED_REPLY;
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 6344d3362df7..f02cc0211b10 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -1041,6 +1041,10 @@ static inline void security_transfer_creds(struct cred *new,
> {
> }
>
> +static inline void security_cred_getsecid(const struct cred *c, u32 *secid)
> +{
> +}
Since security_cred_getsecid() doesn't return an error code we should
probably set the secid to 0 in this case, for example:
static inline void security_cred_getsecid(...)
{
*secid = 0;
}
--
paul moore
www.paul-moore.com
