2.6.36-stable review patch. If anyone has any objections, please let us know.
------------------ From: Nelson Elhage <[email protected]> commit 33dd94ae1ccbfb7bf0fb6c692bc3d1c4269e6177 upstream. 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. [[email protected]: update code comment] Signed-off-by: Nelson Elhage <[email protected]> Cc: KOSAKI Motohiro <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- kernel/exit.c | 9 +++++++++ 1 file changed, 9 insertions(+) --- a/kernel/exit.c +++ b/kernel/exit.c @@ -903,6 +903,15 @@ 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); _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
