Revision 73223e4e2e3867ebf033a5a8eb2e5df0158ccc99 authored by zhong jiang on 18 August 2017, 22:16:24 UTC, committed by Linus Torvalds on 18 August 2017, 22:32:02 UTC
I hit a use after free issue when executing trinity and repoduced it with KASAN enabled. The related call trace is as follows. BUG: KASan: use after free in SyS_get_mempolicy+0x3c8/0x960 at addr ffff8801f582d766 Read of size 2 by task syz-executor1/798 INFO: Allocated in mpol_new.part.2+0x74/0x160 age=3 cpu=1 pid=799 __slab_alloc+0x768/0x970 kmem_cache_alloc+0x2e7/0x450 mpol_new.part.2+0x74/0x160 mpol_new+0x66/0x80 SyS_mbind+0x267/0x9f0 system_call_fastpath+0x16/0x1b INFO: Freed in __mpol_put+0x2b/0x40 age=4 cpu=1 pid=799 __slab_free+0x495/0x8e0 kmem_cache_free+0x2f3/0x4c0 __mpol_put+0x2b/0x40 SyS_mbind+0x383/0x9f0 system_call_fastpath+0x16/0x1b INFO: Slab 0xffffea0009cb8dc0 objects=23 used=8 fp=0xffff8801f582de40 flags=0x200000000004080 INFO: Object 0xffff8801f582d760 @offset=5984 fp=0xffff8801f582d600 Bytes b4 ffff8801f582d750: ae 01 ff ff 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ Object ffff8801f582d760: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk Object ffff8801f582d770: 6b 6b 6b 6b 6b 6b 6b a5 kkkkkkk. Redzone ffff8801f582d778: bb bb bb bb bb bb bb bb ........ Padding ffff8801f582d8b8: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ Memory state around the buggy address: ffff8801f582d600: fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc fc ffff8801f582d680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >ffff8801f582d700: fc fc fc fc fc fc fc fc fc fc fc fc fb fb fb fc !shared memory policy is not protected against parallel removal by other thread which is normally protected by the mmap_sem. do_get_mempolicy, however, drops the lock midway while we can still access it later. Early premature up_read is a historical artifact from times when put_user was called in this path see https://lwn.net/Articles/124754/ but that is gone since 8bccd85ffbaf ("[PATCH] Implement sys_* do_* layering in the memory policy layer."). but when we have the the current mempolicy ref count model. The issue was introduced accordingly. Fix the issue by removing the premature release. Link: http://lkml.kernel.org/r/1502950924-27521-1-git-send-email-zhongjiang@huawei.com Signed-off-by: zhong jiang <zhongjiang@huawei.com> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: David Rientjes <rientjes@google.com> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: <stable@vger.kernel.org> [2.6+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent da094e4
SAK.txt
=========================================
Linux Secure Attention Key (SAK) handling
=========================================
:Date: 18 March 2001
:Author: Andrew Morton
An operating system's Secure Attention Key is a security tool which is
provided as protection against trojan password capturing programs. It
is an undefeatable way of killing all programs which could be
masquerading as login applications. Users need to be taught to enter
this key sequence before they log in to the system.
From the PC keyboard, Linux has two similar but different ways of
providing SAK. One is the ALT-SYSRQ-K sequence. You shouldn't use
this sequence. It is only available if the kernel was compiled with
sysrq support.
The proper way of generating a SAK is to define the key sequence using
``loadkeys``. This will work whether or not sysrq support is compiled
into the kernel.
SAK works correctly when the keyboard is in raw mode. This means that
once defined, SAK will kill a running X server. If the system is in
run level 5, the X server will restart. This is what you want to
happen.
What key sequence should you use? Well, CTRL-ALT-DEL is used to reboot
the machine. CTRL-ALT-BACKSPACE is magical to the X server. We'll
choose CTRL-ALT-PAUSE.
In your rc.sysinit (or rc.local) file, add the command::
echo "control alt keycode 101 = SAK" | /bin/loadkeys
And that's it! Only the superuser may reprogram the SAK key.
.. note::
1. Linux SAK is said to be not a "true SAK" as is required by
systems which implement C2 level security. This author does not
know why.
2. On the PC keyboard, SAK kills all applications which have
/dev/console opened.
Unfortunately this includes a number of things which you don't
actually want killed. This is because these applications are
incorrectly holding /dev/console open. Be sure to complain to your
Linux distributor about this!
You can identify processes which will be killed by SAK with the
command::
# ls -l /proc/[0-9]*/fd/* | grep console
l-wx------ 1 root root 64 Mar 18 00:46 /proc/579/fd/0 -> /dev/console
Then::
# ps aux|grep 579
root 579 0.0 0.1 1088 436 ? S 00:43 0:00 gpm -t ps/2
So ``gpm`` will be killed by SAK. This is a bug in gpm. It should
be closing standard input. You can work around this by finding the
initscript which launches gpm and changing it thusly:
Old::
daemon gpm
New::
daemon gpm < /dev/null
Vixie cron also seems to have this problem, and needs the same treatment.
Also, one prominent Linux distribution has the following three
lines in its rc.sysinit and rc scripts::
exec 3<&0
exec 4>&1
exec 5>&2
These commands cause **all** daemons which are launched by the
initscripts to have file descriptors 3, 4 and 5 attached to
/dev/console. So SAK kills them all. A workaround is to simply
delete these lines, but this may cause system management
applications to malfunction - test everything well.
![swh spinner](/static/img/swh-spinner.gif)
Computing file changes ...