From: Al Viro <viro@zeniv.linux.org.uk>
To: Hao Luo <haoluo@google.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>, KP Singh <kpsingh@kernel.org>,
Shakeel Butt <shakeelb@google.com>,
Joe Burton <jevburton.kernel@gmail.com>,
Tejun Heo <tj@kernel.org>,
joshdon@google.com, sdf@google.com, bpf@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH bpf-next v1 1/9] bpf: Add mkdir, rmdir, unlink syscalls for prog_bpf_syscall
Date: Sat, 12 Mar 2022 03:46:37 +0000 [thread overview]
Message-ID: <YiwXnSGf9Nb79wnm@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <20220225234339.2386398-2-haoluo@google.com>
On Fri, Feb 25, 2022 at 03:43:31PM -0800, Hao Luo wrote:
> This patch allows bpf_syscall prog to perform some basic filesystem
> operations: create, remove directories and unlink files. Three bpf
> helpers are added for this purpose. When combined with the following
> patches that allow pinning and getting bpf objects from bpf prog,
> this feature can be used to create directory hierarchy in bpffs that
> help manage bpf objects purely using bpf progs.
>
> The added helpers subject to the same permission checks as their syscall
> version. For example, one can not write to a read-only file system;
> The identity of the current process is checked to see whether it has
> sufficient permission to perform the operations.
>
> Only directories and files in bpffs can be created or removed by these
> helpers. But it won't be too hard to allow these helpers to operate
> on files in other filesystems, if we want.
In which contexts can those be called?
> +BPF_CALL_2(bpf_rmdir, const char *, pathname, int, pathname_sz)
> +{
> + struct user_namespace *mnt_userns;
> + struct path parent;
> + struct dentry *dentry;
> + int err;
> +
> + if (pathname_sz <= 1 || pathname[pathname_sz - 1])
> + return -EINVAL;
> +
> + err = kern_path(pathname, 0, &parent);
> + if (err)
> + return err;
> +
> + if (!bpf_path_is_bpf_dir(&parent)) {
> + err = -EPERM;
> + goto exit1;
> + }
> +
> + err = mnt_want_write(parent.mnt);
> + if (err)
> + goto exit1;
> +
> + dentry = kern_path_locked(pathname, &parent);
This can't be right. Ever. There is no promise whatsoever
that these two lookups will resolve to the same place.
> +BPF_CALL_2(bpf_unlink, const char *, pathname, int, pathname_sz)
> +{
> + struct user_namespace *mnt_userns;
> + struct path parent;
> + struct dentry *dentry;
> + struct inode *inode = NULL;
> + int err;
> +
> + if (pathname_sz <= 1 || pathname[pathname_sz - 1])
> + return -EINVAL;
> +
> + err = kern_path(pathname, 0, &parent);
> + if (err)
> + return err;
> +
> + err = mnt_want_write(parent.mnt);
> + if (err)
> + goto exit1;
> +
> + dentry = kern_path_locked(pathname, &parent);
> + if (IS_ERR(dentry)) {
> + err = PTR_ERR(dentry);
> + goto exit2;
> + }
Ditto. NAK; if you want to poke into fs/namei.c guts, do it right.
Or at least discuss that on fsdevel. As it is, it's completely broken.
It's racy *and* it blatantly leaks both vfsmount and dentry references.
NAKed-by: Al Viro <viro@zeniv.linux.org.uk>
next prev parent reply other threads:[~2022-03-12 3:46 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-25 23:43 [PATCH bpf-next v1 0/9] Extend cgroup interface with bpf Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 1/9] bpf: Add mkdir, rmdir, unlink syscalls for prog_bpf_syscall Hao Luo
2022-02-27 5:18 ` Kumar Kartikeya Dwivedi
2022-02-28 22:10 ` Hao Luo
2022-03-02 19:34 ` Alexei Starovoitov
2022-03-03 18:50 ` Hao Luo
2022-03-04 18:37 ` Hao Luo
2022-03-05 23:47 ` Alexei Starovoitov
2022-03-08 21:08 ` Hao Luo
2022-03-02 20:55 ` Yonghong Song
2022-03-03 18:56 ` Hao Luo
2022-03-03 19:13 ` Yonghong Song
2022-03-03 19:15 ` Hao Luo
2022-03-12 3:46 ` Al Viro [this message]
2022-03-14 17:07 ` Hao Luo
2022-03-14 23:10 ` Al Viro
2022-03-15 17:27 ` Hao Luo
2022-03-15 18:59 ` Alexei Starovoitov
2022-03-15 19:03 ` Alexei Starovoitov
2022-03-15 19:00 ` Al Viro
2022-03-15 19:47 ` Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 2/9] bpf: Add BPF_OBJ_PIN and BPF_OBJ_GET in the bpf_sys_bpf helper Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 3/9] selftests/bpf: tests mkdir, rmdir, unlink and pin in syscall Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 4/9] bpf: Introduce sleepable tracepoints Hao Luo
2022-03-02 19:41 ` Alexei Starovoitov
2022-03-03 19:37 ` Hao Luo
2022-03-03 19:59 ` Alexei Starovoitov
2022-03-02 21:23 ` Yonghong Song
2022-03-02 21:30 ` Alexei Starovoitov
2022-03-03 1:08 ` Yonghong Song
2022-03-03 2:29 ` Alexei Starovoitov
2022-03-03 19:43 ` Hao Luo
2022-03-03 20:02 ` Alexei Starovoitov
2022-03-03 20:04 ` Alexei Starovoitov
2022-03-03 22:06 ` Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 5/9] cgroup: Sleepable cgroup tracepoints Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 6/9] libbpf: Add sleepable tp_btf Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 7/9] bpf: Lift permission check in __sys_bpf when called from kernel Hao Luo
2022-03-02 20:01 ` Alexei Starovoitov
2022-03-03 19:14 ` Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 8/9] bpf: Introduce cgroup iter Hao Luo
2022-02-26 2:32 ` kernel test robot
2022-02-26 2:32 ` kernel test robot
2022-02-26 2:53 ` kernel test robot
2022-03-02 21:59 ` Yonghong Song
2022-03-03 20:02 ` Hao Luo
2022-03-02 22:45 ` Kumar Kartikeya Dwivedi
2022-03-03 2:03 ` Yonghong Song
2022-03-03 3:03 ` Kumar Kartikeya Dwivedi
2022-03-03 4:00 ` Alexei Starovoitov
2022-03-03 7:33 ` Yonghong Song
2022-03-03 8:13 ` Kumar Kartikeya Dwivedi
2022-03-03 21:52 ` Hao Luo
2022-02-25 23:43 ` [PATCH bpf-next v1 9/9] selftests/bpf: Tests using sleepable tracepoints to monitor cgroup events Hao Luo
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