From mboxrd@z Thu Jan 1 00:00:00 1970 From: tony camuso Subject: Re: [PATCH] drm: assure aux_dev is nonzero before using it Date: Fri, 24 May 2019 06:48:32 -0400 Message-ID: <04ae1fb0-02ab-88e9-94b3-e36f48cc65d5@redhat.com> References: <20190523110905.22445-1-tcamuso@redhat.com> <87v9y0mept.fsf@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <87v9y0mept.fsf@intel.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Jani Nikula , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Cc: airlied@linux.ie, dkwon@redhat.com List-Id: dri-devel@lists.freedesktop.org On 5/24/19 4:36 AM, Jani Nikula wrote: > On Thu, 23 May 2019, tcamuso wrote: >> From Daniel Kwon >> >> The system was crashed due to invalid memory access while trying to access >> auxiliary device. >> >> crash> bt >> PID: 9863 TASK: ffff89d1bdf11040 CPU: 1 COMMAND: "ipmitool" >> #0 [ffff89cedd7f3868] machine_kexec at ffffffffb0663674 >> #1 [ffff89cedd7f38c8] __crash_kexec at ffffffffb071cf62 >> #2 [ffff89cedd7f3998] crash_kexec at ffffffffb071d050 >> #3 [ffff89cedd7f39b0] oops_end at ffffffffb0d6d758 >> #4 [ffff89cedd7f39d8] no_context at ffffffffb0d5bcde >> #5 [ffff89cedd7f3a28] __bad_area_nosemaphore at ffffffffb0d5bd75 >> #6 [ffff89cedd7f3a78] bad_area at ffffffffb0d5c085 >> #7 [ffff89cedd7f3aa0] __do_page_fault at ffffffffb0d7080c >> #8 [ffff89cedd7f3b10] do_page_fault at ffffffffb0d70905 >> #9 [ffff89cedd7f3b40] page_fault at ffffffffb0d6c758 >> [exception RIP: drm_dp_aux_dev_get_by_minor+0x3d] >> RIP: ffffffffc0a589bd RSP: ffff89cedd7f3bf0 RFLAGS: 00010246 >> RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff89cedd7f3fd8 >> RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffc0a613e0 >> RBP: ffff89cedd7f3bf8 R8: ffff89f1bcbabbd0 R9: 0000000000000000 >> R10: ffff89f1be7a1cc0 R11: 0000000000000000 R12: 0000000000000000 >> R13: ffff89f1b32a2830 R14: ffff89d18fadfa00 R15: 0000000000000000 >> ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018 >> RIP: 00002b45f0d80d30 RSP: 00007ffc416066a0 RFLAGS: 00010246 >> RAX: 0000000000000002 RBX: 000056062e212d80 RCX: 00007ffc41606810 >> RDX: 0000000000000000 RSI: 0000000000000002 RDI: 00007ffc41606ec0 >> RBP: 0000000000000000 R8: 000056062dfed229 R9: 00002b45f0cdf14d >> R10: 0000000000000002 R11: 0000000000000246 R12: 00007ffc41606ec0 >> R13: 00007ffc41606ed0 R14: 00007ffc41606ee0 R15: 0000000000000000 >> ORIG_RAX: 0000000000000002 CS: 0033 SS: 002b >> >> ---------------------------------------------------------------------------- >> >> It was trying to open '/dev/ipmi0', but as no entry in aux_dir, it returned >> NULL from 'idr_find()'. This drm_dp_aux_dev_get_by_minor() should have done a >> check on this, but had failed to do it. > > I think the better question is, *why* does the idr_find() return NULL? I > don't think it should, under any circumstances. I fear adding the check > here papers over some other problem, taking us further away from the > root cause. That's a very good question. > Also, can you reproduce this on a recent upstream kernel? The aux device > nodes were introduced in kernel v4.6. Whatever you reproduced on v3.10 > is pretty much irrelevant for upstream. I will look into this deeper, using the upstream kernel. > > > BR, > Jani. -- snip --