[PATCH v2] do_exit(): Make sure we run with get_fs() == USER_DS.

[Nelson Elhage]

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@xxxxxxxxxxx>
---
 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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/