On Mon, 20 Nov 2023, Ville Syrjälä wrote:
> On Mon, Nov 20, 2023 at 10:41:18PM +0800, Edward Adam Davis wrote:
>> [Syz Log]
>> divide error: [#1] PREEMPT SMP KASAN
>> CPU: 0 PID: 5068 Comm: syz-executor357 Not tainted
>> 6.6.0-syzkaller-16039-gac347a0655db #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>> Google 10/09/2023
>> RIP: 0010:drm_mode_vrefresh drivers/gpu/drm/drm_modes.c:1303 [inline]
>> RIP: 0010:drm_mode_debug_printmodeline+0x118/0x4e0
>> drivers/gpu/drm/drm_modes.c:60
>> Code: 00 41 0f b7 07 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 0f af e8
>> 44 89 f0 48 69 c8 e8 03 00 00 89 e8 d1 e8 48 01 c8 31 d2 <48> f7 f5 49 89 c6
>> eb 0c e8 fb 07 66 fc eb 05 e8 f4 07 66 fc 48 89
>> RSP: 0018:c9000391f8d0 EFLAGS: 00010246
>> RAX: 0001f400 RBX: 888025045000 RCX: 0001f400
>> RDX: RSI: 8000 RDI: 888025045018
>> RBP: R08: 8528b9af R09:
>> R10: c9000391f8a0 R11: f52000723f17 R12: 0080
>> R13: dc00 R14: 0080 R15: 888025045016
>> FS: 56932380() GS:8880b980() knlGS:
>> CS: 0010 DS: ES: CR0: 80050033
>> CR2: 005fdeb8 CR3: 7fcff000 CR4: 003506f0
>> DR0: DR1: DR2:
>> DR3: DR6: fffe0ff0 DR7: 0400
>> Call Trace:
>>
>> drm_mode_setcrtc+0x83b/0x1880 drivers/gpu/drm/drm_crtc.c:794
>> drm_ioctl_kernel+0x362/0x500 drivers/gpu/drm/drm_ioctl.c:792
>> drm_ioctl+0x636/0xb00 drivers/gpu/drm/drm_ioctl.c:895
>> vfs_ioctl fs/ioctl.c:51 [inline]
>> __do_sys_ioctl fs/ioctl.c:871 [inline]
>> __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857
>> do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>> do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
>> entry_SYSCALL_64_after_hwframe+0x63/0x6b
>>
>> [Analysis]
>> When calculating den in drm_mode_vrefresh(), if the vscan value is too
>> large,
>> there is a probability of unsigned integer overflow.
>>
>> [Fix]
>> Before multiplying by vscan, first check if their product will overflow.
>> If overflow occurs, return 0 and exit the subsequent process.
>>
>> Reported-and-tested-by: syzbot+2e93e6fb36e6fdc56...@syzkaller.appspotmail.com
>> Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support")
>> Signed-off-by: Edward Adam Davis
>> ---
>> drivers/gpu/drm/drm_modes.c | 7 +--
>> 1 file changed, 5 insertions(+), 2 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
>> index ac9a406250c5..60739d861da2 100644
>> --- a/drivers/gpu/drm/drm_modes.c
>> +++ b/drivers/gpu/drm/drm_modes.c
>> @@ -36,6 +36,7 @@
>> #include
>> #include
>> #include
>> +#include
>>
>> #include
>> #include
>> @@ -1297,8 +1298,10 @@ int drm_mode_vrefresh(const struct drm_display_mode
>> *mode)
>> num *= 2;
>> if (mode->flags & DRM_MODE_FLAG_DBLSCAN)
>> den *= 2;
>> -if (mode->vscan > 1)
>> -den *= mode->vscan;
>> +if (mode->vscan > 1) {
>> +if (unlikely(check_mul_overflow(den, mode->vscan, )))
>> +return 0;
>> +}
>
> I can't see any driver that actually supports vscan>1. Only
> nouveau has some code for it, but doesn't look like it does
> anything sensible. All other drivers for sure should be
> rejecting vscan>1 outright. Which driver is this?
>
> Is there an actual usecase where nouveau needs this (and does
> it even work?) or could we just rip out the whole thing and
> reject vscan>1 globally?
I thought the whole thing seemed familiar [1].
BR,
Jani.
[1] https://lore.kernel.org/r/20230802174746.2256-1-astraj...@yahoo.com
>
>>
>> return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
>> }
>> --
>> 2.25.1
--
Jani Nikula, Intel