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authorNelson Elhage <nelhage@ksplice.com>2010-12-02 14:31:21 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2010-12-02 14:51:16 -0800
commit33dd94ae1ccbfb7bf0fb6c692bc3d1c4269e6177 (patch)
treec00535d8fe9b29be84b02d057e41cd63d7fe3b6b /kernel
parenta0b0f58cdd32ab363a600a294ddaa90f0c32de8c (diff)
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do_exit(): make sure that we run with get_fs() == USER_DS
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. This is only triggerable in the presence of another bug, but this potentially turns a lot of DoS bugs into privilege escalations, so it's worth fixing. I have proof-of-concept code which uses this bug along with CVE-2010-3849 to write a zero to an arbitrary kernel address, so I've tested that this is not theoretical. A more logical place to put this fix 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. [akpm@linux-foundation.org: update code comment] Signed-off-by: Nelson Elhage <nelhage@ksplice.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/exit.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/kernel/exit.c b/kernel/exit.c
index 21aa7b3001f..676149a4ac5 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -914,6 +914,15 @@ 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. Amongst other possible reasons, this is to prevent
+ * mm_release()->clear_child_tid() from writing to a user-controlled
+ * kernel address.
+ */
+ set_fs(USER_DS);
+
tracehook_report_exit(&code);
validate_creds_for_do_exit(tsk);