ptrace: restore smp_rmb() in __ptrace_may_access()

Restore the read memory barrier in __ptrace_may_access() that was deleted
a couple years ago. Also add comments on this barrier and the one it pairs
with to explain why they're there (as far as I understand).

Fixes: bfedb589252c ("mm: Add a user_ns owner to mm_struct and fix ptrace permission checks")
Acked-by: Kees Cook <>
Acked-by: Oleg Nesterov <>
Signed-off-by: Jann Horn <>
Signed-off-by: Eric W. Biederman <>
2 files changed