netdev - Re: [PATCH bpf] bpf: implement dummy fops for bpf objects

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Date:   Fri, 8 Jun 2018 11:05:27 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     ast@...nel.org, netdev@...r.kernel.org
Subject: Re: [PATCH bpf] bpf: implement dummy fops for bpf objects

On Fri, Jun 08, 2018 at 06:10:34PM +0200, Daniel Borkmann wrote:
> syzkaller was able to trigger the following warning in
> do_dentry_open():
> 
>   WARNING: CPU: 1 PID: 4508 at fs/open.c:778 do_dentry_open+0x4ad/0xe40 fs/open.c:778
>   Kernel panic - not syncing: panic_on_warn set ...
> 
>   CPU: 1 PID: 4508 Comm: syz-executor867 Not tainted 4.17.0+ #90
>   Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>   Call Trace:
>   [...]
>    vfs_open+0x139/0x230 fs/open.c:908
>    do_last fs/namei.c:3370 [inline]
>    path_openat+0x1717/0x4dc0 fs/namei.c:3511
>    do_filp_open+0x249/0x350 fs/namei.c:3545
>    do_sys_open+0x56f/0x740 fs/open.c:1101
>    __do_sys_openat fs/open.c:1128 [inline]
>    __se_sys_openat fs/open.c:1122 [inline]
>    __x64_sys_openat+0x9d/0x100 fs/open.c:1122
>    do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>    entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Problem was that prog and map inodes in bpf fs did not
> implement a dummy file open operation that would return an
> error. The patch in do_dentry_open() checks whether f_ops
> are present and if not bails out with an error. While this
> may be fine, we really shouldn't be throwing a warning
> though. Thus follow the model similar to bad_file_ops and
> reject the request unconditionally with -EIO.
> 
> Fixes: b2197755b263 ("bpf: add support for persistent maps/progs")
> Reported-by: syzbot+2e7fcab0f56fdbb330b8@...kaller.appspotmail.com
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>

Applied, Thanks