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);
+
tracehook_report_exit(&code);
validate_creds_for_do_exit(tsk);
--
1.7.1.31.g6297e
--
