Re: [syzbot] BUG: bad usercopy in io_openat2_prep

[Dmitry Vyukov <dvyukov@google.com>]

On Mon, 13 Feb 2023 at 12:05, Kees Cook <kees@kernel.org> wrote:
>
> On February 11, 2023 8:08:52 AM PST, syzbot <syzbot+cdd9922704fc75e03ffc@syzkaller.appspotmail.com> wrote:
> >Hello,
> >
> >syzbot found the following issue on:
> >
> >HEAD commit:    ca72d58361ee Merge branch 'for-next/core' into for-kernelci
> >git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
> >console output: https://syzkaller.appspot.com/x/log.txt?x=14a882f3480000
> >kernel config:  https://syzkaller.appspot.com/x/.config?x=f3e78232c1ed2b43
> >dashboard link: https://syzkaller.appspot.com/bug?extid=cdd9922704fc75e03ffc
> >compiler:       Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2
> >userspace arch: arm64
> >syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1203777b480000
> >C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=124c1ea3480000
> >
> >Downloadable assets:
> >disk image: https://storage.googleapis.com/syzbot-assets/e2c91688b4cd/disk-ca72d583.raw.xz
> >vmlinux: https://storage.googleapis.com/syzbot-assets/af105438bee6/vmlinux-ca72d583.xz
> >kernel image: https://storage.googleapis.com/syzbot-assets/4a28ec4f8f7e/Image-ca72d583.gz.xz
> >
> >IMPORTANT: if you fix the issue, please add the following tag to the commit:
> >Reported-by: syzbot+cdd9922704fc75e03ffc@syzkaller.appspotmail.com
> >
> >usercopy: Kernel memory overwrite attempt detected to SLUB object 'pid' (offset 24, size 24)!
>
> This looks like some serious memory corruption. The pid slab is 24 bytes in size, but struct io_open is larger... Possible UAF after the memory being reallocated to a new slab??

We've just noticed that some of syzbot arm64 configs did not enable
KASAN, so it could produce false one-off reports caused by previous
silent memory corruptions.

So if you don't see anything obvious, don't spend too much time looking at it.

#syz invalid


> -Kees
>
> > [...]
> >Call trace:
> > usercopy_abort+0x90/0x94
> > __check_heap_object+0xa8/0x100
> > __check_object_size+0x208/0x6b8
> > io_openat2_prep+0xcc/0x2b8
> > io_submit_sqes+0x338/0xbb8
> > __arm64_sys_io_uring_enter+0x168/0x1308
> > invoke_syscall+0x64/0x178
> > el0_svc_common+0xbc/0x180
> > do_el0_svc+0x48/0x110
> > el0_svc+0x58/0x14c
> > el0t_64_sync_handler+0x84/0xf0
> > el0t_64_sync+0x190/0x194
>
>
>
> --
> Kees Cook