The patch titled
do_exit(): make sure that we run with get_fs() == USER_DS.
has been added to the -mm tree. Its filename is
do_exit-make-sure-we-run-with-get_fs-==-user_ds.patch
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------------------------------------------------------
Subject: do_exit(): make sure that we run with get_fs() == USER_DS.
From: Nelson Elhage <nelhage@xxxxxxxxxxx>
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>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/exit.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff -puN kernel/exit.c~do_exit-make-sure-we-run-with-get_fs-==-user_ds kernel/exit.c
--- a/kernel/exit.c~do_exit-make-sure-we-run-with-get_fs-==-user_ds
+++ a/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);
_
Patches currently in -mm which might be from nelhage@xxxxxxxxxxx are
do_exit-make-sure-we-run-with-get_fs-==-user_ds.patch
do_exit-make-sure-we-run-with-get_fs-==-user_ds-fix.patch
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