UBSAN: shift-out-of-bounds in std_validate

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 1e2a199f Merge tag 'spi-fix-v5.11-rc4' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=146e0c94d00000
kernel config: https://syzkaller.appspot.com/x/.config?x=41e68e7e8a23ad09
dashboard link: https://syzkaller.appspot.com/bug?extid=42d8c7c3d3e594b34346
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12166d58d00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14dfc294d00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+42d8c7...@syzkaller.appspotmail.com

================================================================================
UBSAN: shift-out-of-bounds in drivers/media/v4l2-core/v4l2-ctrls.c:2168:36
shift exponent 100 is too large for 64-bit type 'long long unsigned int'
CPU: 0 PID: 8469 Comm: syz-executor534 Not tainted 5.11.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0x107/0x163 lib/dump_stack.c:120
ubsan_epilogue+0xb/0x5a lib/ubsan.c:148
__ubsan_handle_shift_out_of_bounds.cold+0xb1/0x181 lib/ubsan.c:395
std_validate.cold+0x19/0x1e drivers/media/v4l2-core/v4l2-ctrls.c:2168
validate_new drivers/media/v4l2-core/v4l2-ctrls.c:2477 [inline]
set_ctrl+0x207/0x4a0 drivers/media/v4l2-core/v4l2-ctrls.c:4425
set_ctrl_lock drivers/media/v4l2-core/v4l2-ctrls.c:4448 [inline]
v4l2_s_ctrl+0x2fd/0x4f0 drivers/media/v4l2-core/v4l2-ctrls.c:4469
v4l_s_ctrl+0x324/0x390 drivers/media/v4l2-core/v4l2-ioctl.c:2253
__video_do_ioctl+0xb94/0xe20 drivers/media/v4l2-core/v4l2-ioctl.c:2993
video_usercopy+0x23d/0x12d0 drivers/media/v4l2-core/v4l2-ioctl.c:3345
v4l2_ioctl+0x1b3/0x250 drivers/media/v4l2-core/v4l2-dev.c:360
vfs_ioctl fs/ioctl.c:48 [inline]
__do_sys_ioctl fs/ioctl.c:753 [inline]
__se_sys_ioctl fs/ioctl.c:739 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x443ee9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 fb d7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffe02e7df08 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004002e0 RCX: 0000000000443ee9
RDX: 0000000020000140 RSI: 00000000c008561c RDI: 0000000000000003
RBP: 00000000006ce018 R08: 0000000000000000 R09: 00000000004002e0
R10: 000000000000000f R11: 0000000000000246 R12: 0000000000401b70
R13: 0000000000401c00 R14: 0000000000000000 R15: 0000000000000000
================================================================================


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[Francis Laniel]

Hi everyone.


First, I hope you are fine and the same for your relative.

I took a look at this bug, unfortunately I do not come with a solution as I
lack some background on V4L2.

First, I successfully reproduced the bug with the given test and configuration
inside a virtual machine.
From my understanding, the test do an ioctl with the flag VIDIOC_S_CTRL and the
value 100 as argument.
Inside the std_validate() function, ctrl->maximum is 110 as it corresponds to
this line inside the vivid_create_controls() function:
vivid_ctrl_dv_timings.max = dev->query_dv_timings_size - 1;
dev->query_dv_timings_size is set inside vivid_init_dv_timings() based on the
v4l2_dv_timings_presets[] which contains 110 values.

As a solution, I suggest to change the type of menu_skip_mask inside the
struct v4l2_ctrl and replacing it with a bitmap.
Indeed, the above value has 110 "menus", so the 64 bits inside menu_skip_mask
are too few.
This change needs a bit of work as all the usage of menu_skip_mask will need
to be adapted to the bitmap API.
Unfortunately, I am not sure this solution is the good one so this I why I did
not implement it.

If someone also looked at this bug and has some feedback I will be happy to
hear from it.


Best regards.