Re: [syzbot] BUG: bad usercopy in io_openat2_prep

[Pavel Begunkov]

On 2/11/23 16:36, Kees Cook wrote:
> On February 11, 2023 8:08:52 AM PST, syzbot <syzbot+cdd9922704fc75e03ffc@xxxxxxxxxxxxxxxxxxxxxxxxx> 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

I couldn't reproduce it, let's try latest io_uring first

#syz test: https://git.kernel.dk/linux.git for-6.3/io_uring


> > 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > 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??
>
> -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

--
Pavel Begunkov