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Date:   Tue, 9 Mar 2021 14:25:36 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Palash Oswal <oswalpalash@gmail.com>
Cc:     akpm@linux-foundation.org, dave@stgolabs.net,
        Kees Cook <keescook@chromium.org>,
        linux-kernel@vger.kernel.org, mingo@kernel.org,
        peterz@infradead.org, rppt@linux.vnet.ibm.com, sds@tycho.nsa.gov,
        syzkaller-bugs@googlegroups.com
Subject: Re: kernel panic: Attempted to kill init!
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On Tue, Mar 09, 2021 at 11:29:14AM +0530, Palash Oswal wrote:

> I observe the following result(notice the segfault in systemd):
> root@sandbox:~# ./repro
> [    9.457767] got to 221
> [    9.457791] got to 183
> [    9.459144] got to 201
> [    9.459471] got to 208
> [    9.459773] got to 210
> [    9.462602] got to 270
> [    9.488551] systemd[1]: segfault at 7ffe59fd7fb8 ip
> 000055be8f20b466 sp 00007ffe59fd7fc0 error 6 in
> systemd[55be8f15f000+ed000]
> [    9.490723] Code: 00 00 00 00 41 57 41 56 41 55 41 54 55 53 89 fd
> 48 81 ec 48 01 00 00 64 48 8b 04 25 28 00 00 00 48 89 84 24 38 01 00
> 00 31 c0 <e8> f5 bf f7 ff 83 f8 01 0f 84 b7 00 00 00 48 8d 9c 240
> [    9.492637] Kernel panic - not syncing: Attempted to kill init!
> exitcode=0x0000000b

Lovely.  So something in that sequence of syscalls manages to trigger
segfault in unrelated process.  What happens if you put it to sleep
right after open_by_handle_at() (e.g. by read(2) from fd 0, etc.)?