Re: WARNING in drm_mode_createblob_ioctl

[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 :-/
-Daniel
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+fb77e97ebf0612ee6914@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ------------[ 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
> 
> 
> ---
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> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch