Subject: Re: [syzbot] [mm?] [hardening?] BUG: bad usercopy in raw_getsockopt

From: Kees Cook <[email-masked]>
Date: Tue, 20 Feb 2024 10:46:52 -0800

On Tue, Feb 20, 2024 at 05:28:17PM +0100, Oliver Hartkopp wrote:
> The issue has already been fixed with the next commit in net-next:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=c8fba5d6df5e476aa791db4f1f014dad2bb5e904
> 
> Sorry for the effort - but really good to see, that the problem has been
> catched automatically. Good job!

Thanks!

And this also nicely demonstrated the zero-init mitigation as well: the
uninitialized "val" pointer was NULL, not random stack contents. :)

#syz fix: can: raw: fix getsockopt() for new CAN_RAW_XL_VCID_OPTS

-Kees

> 
> Best regards,
> Oliver
> 
> On 2024-02-20 16:40, syzbot wrote:
> > Hello,
> > 
> > syzbot found the following issue on:
> > 
> > HEAD commit:    74293ea1c4db net: sysfs: Do not create sysfs for non BQL d..
> > git tree:       net-next
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=13dcc4b4180000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=970c7b6c80a096da
> > dashboard link: https://syzkaller.appspot.com/bug?extid=0c35af046fa98c893c84
> > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10f38cf8180000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=136d41c2180000
> > 
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/9bca2f6e074e/disk-74293ea1.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/611a08387d8f/vmlinux-74293ea1.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/78c388071345/bzImage-74293ea1.xz
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: [email-masked]
> > 
> > usercopy: Kernel memory exposure attempt detected from null address (offset 0, size 4)!
> > ------------[ cut here ]------------
> > kernel BUG at mm/usercopy.c:102!
> > invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
> > CPU: 1 PID: 5070 Comm: syz-executor201 Not tainted 6.8.0-rc4-syzkaller-01053-g74293ea1c4db #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
> > RIP: 0010:usercopy_abort+0x84/0x90 mm/usercopy.c:102
> > Code: 49 89 ce 48 c7 c3 40 db b7 8b 48 0f 44 de 48 c7 c7 e0 d9 b7 8b 4c 89 de 48 89 c1 41 52 41 56 53 e8 01 c5 60 09 48 83 c4 18 90 <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90
> > RSP: 0018:ffffc90003a3fc50 EFLAGS: 00010296
> > RAX: 0000000000000057 RBX: ffffffff8bb7db20 RCX: b071ef5fcc834300
> > RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
> > RBP: ffffffffffffffff R08: ffffffff81753e6c R09: 1ffff92000747f28
> > R10: dffffc0000000000 R11: fffff52000747f29 R12: 0000000000000001
> > R13: 0000000000000004 R14: 0000000000000000 R15: 0000000000000000
> > FS:  0000555555f8e380(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000000020001480 CR3: 000000001f404000 CR4: 00000000003506f0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> >   <TASK>
> >   __check_object_size+0x601/0xa00
> >   check_object_size include/linux/thread_info.h:215 [inline]
> >   check_copy_size include/linux/thread_info.h:251 [inline]
> >   copy_to_user include/linux/uaccess.h:190 [inline]
> >   raw_getsockopt+0x37a/0x490 net/can/raw.c:852
> >   do_sock_getsockopt+0x373/0x850 net/socket.c:2373
> >   __sys_getsockopt+0x270/0x330 net/socket.c:2402
> >   __do_sys_getsockopt net/socket.c:2412 [inline]
> >   __se_sys_getsockopt net/socket.c:2409 [inline]
> >   __x64_sys_getsockopt+0xb5/0xd0 net/socket.c:2409
> >   do_syscall_64+0xf9/0x240
> >   entry_SYSCALL_64_after_hwframe+0x6f/0x77
> > RIP: 0033:0x7f21bfe782a9
> > Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> > RSP: 002b:00007ffcdfc8f038 EFLAGS: 00000246 ORIG_RAX: 0000000000000037
> > RAX: ffffffffffffffda RBX: 00007ffcdfc8f208 RCX: 00007f21bfe782a9
> > RDX: 0000000000000008 RSI: 0000000000000065 RDI: 0000000000000003
> > RBP: 00007f21bfeeb610 R08: 0000000020001480 R09: 00007ffcdfc8f208
> > R10: 0000000020001440 R11: 0000000000000246 R12: 0000000000000001
> > R13: 00007ffcdfc8f1f8 R14: 0000000000000001 R15: 0000000000000001
> >   </TASK>
> > Modules linked in:
> > ---[ end trace 0000000000000000 ]---
> > RIP: 0010:usercopy_abort+0x84/0x90 mm/usercopy.c:102
> > Code: 49 89 ce 48 c7 c3 40 db b7 8b 48 0f 44 de 48 c7 c7 e0 d9 b7 8b 4c 89 de 48 89 c1 41 52 41 56 53 e8 01 c5 60 09 48 83 c4 18 90 <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90
> > RSP: 0018:ffffc90003a3fc50 EFLAGS: 00010296
> > RAX: 0000000000000057 RBX: ffffffff8bb7db20 RCX: b071ef5fcc834300
> > RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
> > RBP: ffffffffffffffff R08: ffffffff81753e6c R09: 1ffff92000747f28
> > R10: dffffc0000000000 R11: fffff52000747f29 R12: 0000000000000001
> > R13: 0000000000000004 R14: 0000000000000000 R15: 0000000000000000
> > FS:  0000555555f8e380(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000000020001480 CR3: 000000001f404000 CR4: 00000000003506f0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > 
> > 
> > ---
> > This report 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 [email-masked].
> > 
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > 
> > If the report is already addressed, let syzbot know by replying with:
> > #syz fix: exact-commit-title
> > 
> > If you want syzbot to run the reproducer, reply with:
> > #syz test: git://repo/address.git branch-or-commit-hash
> > If you attach or paste a git patch, syzbot will apply it before testing.
> > 
> > If you want to overwrite report's subsystems, reply with:
> > #syz set subsystems: new-subsystem
> > (See the list of subsystem names on the web dashboard)
> > 
> > If the report is a duplicate of another one, reply with:
> > #syz dup: exact-subject-of-another-report
> > 
> > If you want to undo deduplication, reply with:
> > #syz undup
> > 

-- 
Kees Cook