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Subject: Re: WARNING in drm_mode_createblob_ioctl
To:     syzbot <syzbot+fb77e97ebf0612ee6914@syzkaller.appspotmail.com>,
        airlied@linux.ie, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, mripard@kernel.org, sean@poorly.run,
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References: <000000000000b2de3a0594d8b4ca@google.com>
 <20191014091635.GI11828@phenom.ffwll.local>
From:   syzbot <syzbot+fb77e97ebf0612ee6914@syzkaller.appspotmail.com>
Message-ID: <67fb1a91-7ef3-9036-2d1b-877e394bcab2@linux.intel.com>
Date:   Mon, 14 Oct 2019 11:39:38 +0200
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Op 14-10-2019 om 11:16 schreef Daniel Vetter:
> On Sun, Oct 13, 2019 at 11:09:09PM -0700, syzbot wrote:
>> Hello,
>>
>> syzbot found the following crash on:
>>
>> HEAD commit:    8ada228a Add linux-next specific files for 20191011
>> git tree:       linux-next
>> console output: https://syzkaller.appspot.com/x/log.txt?x=1423a87f600000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=7cf4eed5fe42c31a
>> dashboard link: https://syzkaller.appspot.com/bug?extid=fb77e97ebf0612ee6914
>> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>>
>> Unfortunately, I don't have any reproducer for this crash yet.
> Hm only thing that could go wrong is how we allocate the target for the
> user_copy, which is an argument directly from the ioctl parameter struct.
> Does syzbot not track that? We use the standard linux ioctl struct
> encoding in drm.
>
> Otherwise I have no idea why it can't create a reliable reproducer for
> this ... I'm also not seeing the bug, all the input validation we have
> seems correct :-/

I would like to see the entire dmesg?

in particular because it's likely WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count),

so I'd like to see the size it thinks for both..

> -Daniel
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+fb77e97ebf0612ee6914@syzkaller.appspotmail.com
>>
>> ------------[ cut here ]------------
>> WARNING: CPU: 1 PID: 30449 at include/linux/thread_info.h:150
>> check_copy_size include/linux/thread_info.h:150 [inline]
>> WARNING: CPU: 1 PID: 30449 at include/linux/thread_info.h:150 copy_from_user
>> include/linux/uaccess.h:143 [inline]
>> WARNING: CPU: 1 PID: 30449 at include/linux/thread_info.h:150
>> drm_mode_createblob_ioctl+0x398/0x490 drivers/gpu/drm/drm_property.c:800
>> Kernel panic - not syncing: panic_on_warn set ...
>> CPU: 1 PID: 30449 Comm: syz-executor.5 Not tainted 5.4.0-rc2-next-20191011
>> #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>> Google 01/01/2011
>> Call Trace:
>>  __dump_stack lib/dump_stack.c:77 [inline]
>>  dump_stack+0x172/0x1f0 lib/dump_stack.c:113
>>  panic+0x2e3/0x75c kernel/panic.c:221
>>  __warn.cold+0x2f/0x35 kernel/panic.c:582
>>  report_bug+0x289/0x300 lib/bug.c:195
>>  fixup_bug arch/x86/kernel/traps.c:174 [inline]
>>  fixup_bug arch/x86/kernel/traps.c:169 [inline]
>>  do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:267
>>  do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:286
>>  invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1028
>> RIP: 0010:check_copy_size include/linux/thread_info.h:150 [inline]
>> RIP: 0010:copy_from_user include/linux/uaccess.h:143 [inline]
>> RIP: 0010:drm_mode_createblob_ioctl+0x398/0x490
>> drivers/gpu/drm/drm_property.c:800
>> Code: c1 ea 03 80 3c 02 00 0f 85 ed 00 00 00 49 89 5d 00 e8 3c 28 cb fd 4c
>> 89 f7 e8 64 92 9e 03 31 c0 e9 75 fd ff ff e8 28 28 cb fd <0f> 0b e8 21 28 cb
>> fd 4d 85 e4 b8 f2 ff ff ff 0f 84 5b fd ff ff 89
>> RSP: 0018:ffff8880584efaa8 EFLAGS: 00010246
>> RAX: 0000000000040000 RBX: ffff8880a3a90000 RCX: ffffc900109da000
>> RDX: 0000000000040000 RSI: ffffffff83a7eaf8 RDI: 0000000000000007
>> RBP: ffff8880584efae8 R08: ffff888096c40080 R09: ffffed1014752110
>> R10: ffffed101475210f R11: ffff8880a3a9087f R12: ffffc90014907000
>> R13: ffff888028aa0000 R14: 000000009a6c7969 R15: ffffc90014907058
>>
>>
>> ---
>> This bug is generated by a bot. It may contain errors.
>> See https://goo.gl/tpsmEJ for more information about syzbot.
>> syzbot engineers can be reached at syzkaller@googlegroups.com.
>>
>> syzbot will keep track of this bug report. See:
>> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.