On Wed, Dec 23, 2020 at 07:11:38PM +0900, Tetsuo Handa wrote:
> due to commit 5e6e9852d6f76e01 ("uaccess: add infrastructure for kernel
> builds with set_fs()") and follow up changes. Don't we need to change this
> "uaccess_kernel()" with "(current->flags & PF_KTHREAD)" ?No. The real problem here is that when a this funtion is called under set_fs it allows kernel memory access for all user pointers, and due to the indirection in the playload allows reading or changing kernel memory. A kthread does not have that issue. > >> For another example, if uaccess_kernel() is "false" due to CONFIG_SET_FS=n, > >> isn't TOMOYO unexpectedly checking permissions for socket operations? > > > > Can someone explain WTF TOMOYO is even doing there? A security module > > has absolutely no business checking what context it is called from, but > > must check the process credentials instead. > > > > TOMOYO distinguishes userspace processes and kernel threads, and grants > kernel threads implicit permissions to perform socket operations. And this is the problem we need to fix. A kernel thread can't just have implicit permissions only because it is a kernel thread. Think of e.g. the io_uring service threads.
