Commit db68ce10c4f0a27c ("new helper: uaccess_kernel()") replaced
segment_eq(get_fs(), KERNEL_DS)
with uaccess_kernel(). But uaccess_kernel() became an unconditional "false" for
some architectures
due to commit 5e6e9852d6f76e01 ("uaccess: add infrastructure for kernel builds
with set_fs()") and
follow up changes in Linux 5.10. As a result, I guess that uaccess_kernel() can
no longer be used
as a condition for checking whether current thread is a kernel thread or not.
For example, if uaccess_kernel() is "false" due to CONFIG_SET_FS=n,
isn't sg_check_file_access() failing to detect kernel context?
static int sg_check_file_access(struct file *filp, const char *caller)
{
if (filp->f_cred != current_real_cred()) {
pr_err_once("%s: process %d (%s) changed security contexts
after opening file descriptor, this is not allowed.\n",
caller, task_tgid_vnr(current), current->comm);
return -EPERM;
}
if (uaccess_kernel()) {
pr_err_once("%s: process %d (%s) called from kernel context,
this is not allowed.\n",
caller, task_tgid_vnr(current), current->comm);
return -EACCES;
}
return 0;
}
For another example, if uaccess_kernel() is "false" due to CONFIG_SET_FS=n,
isn't TOMOYO unexpectedly checking permissions for socket operations?
static bool tomoyo_kernel_service(void)
{
/* Nothing to do if I am a kernel service. */
return uaccess_kernel();
}
static u8 tomoyo_sock_family(struct sock *sk)
{
u8 family;
if (tomoyo_kernel_service())
return 0;
family = sk->sk_family;
switch (family) {
case PF_INET:
case PF_INET6:
case PF_UNIX:
return family;
default:
return 0;
}
}
Don't we need to replace such usage with something like (current->flags &
PF_KTHREAD) ?
I don't know about io_uring, but according to
https://lkml.kernel.org/r/dacfb329-de66-d0cf-dcf9-f030ea137...@schaufler-ca.com
,
should (current->flags & (PF_KTHREAD | PF_IO_WORKER)) == PF_KTHREAD be used
instead?
