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27 March 2024, 02:37:15 UTC
Revision 33dd94ae1ccbfb7bf0fb6c692bc3d1c4269e6177 authored by Nelson Elhage on 02 December 2010, 22:31:21 UTC, committed by Linus Torvalds on 02 December 2010, 22:51:16 UTC 
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>
1 parent a0b0f58
History
Tip revision: 33dd94ae1ccbfb7bf0fb6c692bc3d1c4269e6177 authored by Nelson Elhage on 02 December 2010, 22:31:21 UTC
do_exit(): make sure that we run with get_fs() == USER_DS
Tip revision: 33dd94a
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