Re: [syzbot] [io-uring?] UBSAN: array-index-out-of-bounds in io_setup_async_msg

Pavel Begunkov
2023-09-13T13:10:33Z

On 9/13/23 13:11, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 0bb80ecc33a8 Linux 6.6-rc1
> git tree: upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=12d1eb78680000
> kernel config: https://syzkaller.appspot.com/x/.config?x=f4894cf58531f
> dashboard link: https://syzkaller.appspot.com/bug?extid=a4c6e5ef999b68b26ed1
> compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16613002680000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13912e30680000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/eeb0cac260c7/disk-0bb80ecc.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/a3c360110254/vmlinux-0bb80ecc.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/22b81065ba5f/bzImage-0bb80ecc.xz
>
> The issue was bisected to:
>
> commit 2af89abda7d9c2aeb573677e2c498ddb09f8058a
> Author: Pavel Begunkov <asml.silence@gmail.com>
> Date: Thu Aug 24 22:53:32 2023 +0000
>
> io_uring: add option to remove SQ indirection
>
> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=15892e30680000
> final oops: https://syzkaller.appspot.com/x/report.txt?x=17892e30680000
> console output: https://syzkaller.appspot.com/x/log.txt?x=13892e30680000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+a4c6e5ef999b68b26ed1@syzkaller.appspotmail.com
> Fixes: 2af89abda7d9 ("io_uring: add option to remove SQ indirection")
>
> ================================================================================
> UBSAN: array-index-out-of-bounds in io_uring/net.c:189:55
> index 3779567444058 is out of range for type 'iovec [8]'
> CPU: 1 PID: 5039 Comm: syz-executor396 Not tainted 6.6.0-rc1-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/04/2023
> Call Trace:
> <TASK>
> __dump_stack lib/dump_stack.c:88 [inline]
> dump_stack_lvl+0x125/0x1b0 lib/dump_stack.c:106
> ubsan_epilogue lib/ubsan.c:217 [inline]
> __ubsan_handle_out_of_bounds+0x111/0x150 lib/ubsan.c:348
> io_setup_async_msg+0x2a0/0x2b0 io_uring/net.c:189

Which is

/* if were using fast_iov, set it to the new one */
if (iter_is_iovec(&kmsg->msg.msg_iter) && !kmsg->free_iov) {
size_t fast_idx = iter_iov(&kmsg->msg.msg_iter) - kmsg->fast_iov;
async_msg->msg.msg_iter.__iov = &async_msg->fast_iov[fast_idx];
}

The bisection doesn't immediately make sense, I'll try
it out