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| author | Nelson Elhage <nelhage@ksplice.com> | 2010-12-02 14:31:21 -0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2010-12-09 13:24:19 -0800 |
| commit | ec1793bd760a355fb69468f01705d3267651f8ca (patch) | |
| tree | cc933e03ef5f8a7a721edb66c29bcdd9ebe8baa6 | |
| parent | 8d41cfeeacabaaace31b13071a46b8e0e4afb592 (diff) | |
| download | lwn-ec1793bd760a355fb69468f01705d3267651f8ca.tar.gz lwn-ec1793bd760a355fb69468f01705d3267651f8ca.zip | |
do_exit(): make sure that we run with get_fs() == USER_DS
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.
[akpm@linux-foundation.org: update code comment]
Signed-off-by: Nelson Elhage <nelhage@ksplice.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
| -rw-r--r-- | kernel/exit.c | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/kernel/exit.c b/kernel/exit.c index 8715136aca46..ac5ab8c683b0 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -1004,6 +1004,15 @@ 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); /* |