drm: GPF in drm_getcap

[David Herrmann]

Hi

On Sat, Nov 26, 2016 at 6:17 PM, Dmitry Vyukov <dvyukov at google.com> wrote:
> On Fri, Sep 9, 2016 at 1:56 PM, Dmitry Vyukov <dvyukov at google.com> wrote:
>> Hello,
>>
>> The following program triggers GPF in drm_getcap:
>>
>> // autogenerated by syzkaller (http://github.com/google/syzkaller)
>> #include <fcntl.h>
>> #include <stddef.h>
>> #include <stdint.h>
>> #include <sys/ioctl.h>
>> #include <sys/stat.h>
>> #include <sys/syscall.h>
>> #include <sys/types.h>
>> #include <unistd.h>
>>
>> int main()
>> {
>>   int fd = open("/dev/dri/card0", O_RDONLY);
>>   uint64_t data[2] = {0x11, 0x80};
>>   ioctl(fd, 0xc010640cul /*DRM_IOCTL_GET_CAP*/, data);
>>   return 0;
>> }
>>
>>
>> general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN
>> Modules linked in:
>> CPU: 1 PID: 5745 Comm: syz-executor Not tainted 4.8.0-rc5-next-20160905+ #14
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>> task: ffff8800310dc540 task.stack: ffff88003cbc0000
>> RIP: 0010:[<ffffffff834ca87b>]  [<ffffffff834ca87b>]
>> drm_getcap+0x34b/0x4f0 drivers/gpu/drm/drm_ioctl.c:260
>> RSP: 0018:ffff88003cbc7c28  EFLAGS: 00010202
>> RAX: 0000000000000058 RBX: ffff88003cbc7cf8 RCX: ffffc90001db0000
>> RDX: 000000000000005d RSI: ffff88003cbc7cf8 RDI: 00000000000002c0
>> RBP: ffff88003cbc7c50 R08: ffffed0007978fa1 R09: ffffed0007978fa0
>> R10: ffff88003cbc7d07 R11: ffffed0007978fa1 R12: fffffffffffffff0
>> R13: dffffc0000000000 R14: ffff88003bcc6850 R15: fffffffffffffff2
>> FS:  00007fcbf4e03700(0000) GS:ffff88003ed00000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00000000006dce00 CR3: 0000000066135000 CR4: 00000000000006e0
>> DR0: 000000000000001e DR1: 000000000000001e DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
>> Stack:
>>  ffff88003c26db00 ffff88003cbc7cf8 ffffffff875a3000 ffffffff88cf0ee0
>>  fffffffffffffff2 ffff88003cbc7dc0 ffffffff834cb57c 000000000000e200
>>  1ffff10000000001 ffffffff875a1ba0 ffffffff882ae930 0000000000000010
>> Call Trace:
>>  [<ffffffff834cb57c>] drm_ioctl+0x54c/0xaf0 drivers/gpu/drm/drm_ioctl.c:728
>>  [<     inline     >] vfs_ioctl fs/ioctl.c:43
>>  [<ffffffff818a331c>] do_vfs_ioctl+0x18c/0x1080 fs/ioctl.c:675
>>  [<     inline     >] SYSC_ioctl fs/ioctl.c:690
>>  [<ffffffff818a429f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:681
>>  [<ffffffff86e1a8c0>] entry_SYSCALL_64_fastpath+0x23/0xc1
>> Code: 3c 28 00 0f 85 88 01 00 00 49 8b 44 24 10 49 39 c6 4c 8d 60 f0
>> 74 82 e8 64 19 10 fe 49 8d bc 24 d0 02 00 00 48 89 f8 48 c1 e8 03 <42>
>> 80 3c 28 00 0f 85 6f 01 00 00 4d 8b bc 24 d0 02 00 00 49 8d
>> RIP  [<ffffffff834ca87b>] drm_getcap+0x34b/0x4f0 drivers/gpu/drm/drm_ioctl.c:260
>>  RSP <ffff88003cbc7c28>
>> ---[ end trace c6e1afa8cd73b880 ]---
>>
>>
>> On commit 4affa544adb8077403893e62b9e327fcf87de6f7 (Sep 8) of linux-next.
>
> ping
>
> Still happens on 16ae16c6e5616c084168740990fc508bda6655d4 (Nov 24).

I suspect this is because we run drm_for_each_crtc() in
drm_getcap(DRM_PAGE_FLIP_TARGET) on a legacy driver (meaning
mode_config is not initialized). @danvet, how about always
initializing mode_config to 0/empty/dummy?

Dmitry, what driver do you run this on? And is CONFIG_DRM_LEGACY enabled?

Thanks
David