Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: [PATCH v2] do_exit(): Make sure we run with get_fs() == USER_DS. | Date | Wed, 1 Dec 2010 11:50:32 +0900 (JST) |
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> If a user manages to trigger an oops with fs set to KERNEL_DS, fs is not > otherwise reset before do_exit(). do_exit may later (via mm_release in fork.c) > do a put_user to a user-controlled address, potentially allowing a user to > leverage an oops into a controlled write into kernel memory. > > A more logical place to put this might be when we know an oops has occurred, > before we call do_exit(), but that would involve changing every architecture, in > multiple places. Let's just stick it in do_exit instead. > > Signed-off-by: Nelson Elhage <nelhage@ksplice.com> > --- > kernel/exit.c | 8 ++++++++ > 1 files changed, 8 insertions(+), 0 deletions(-) > > diff --git a/kernel/exit.c b/kernel/exit.c > index 21aa7b3..68899b3 100644 > --- a/kernel/exit.c > +++ b/kernel/exit.c > @@ -914,6 +914,14 @@ NORET_TYPE void do_exit(long code) > if (unlikely(!tsk->pid)) > panic("Attempted to kill the idle task!"); > > + /* > + * If do_exit is called because this processes oopsed, it's possible > + * that get_fs() was left as KERNEL_DS, so reset it to USER_DS before > + * continuing. This is relevant at least for clearing clear_child_tid in > + * mm_release. > + */ > + set_fs(USER_DS);
"This is relevant" is no good explanation ;) Please recognize this is tricky code and Please consider to write more careful and looooong comments.
Thanks.
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