From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Wenbo Zhang <ethercflow@gmail.com>
Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
yhs@fb.com, andrii.nakryiko@gmail.com, netdev@vger.kernel.org
Subject: Re: [PATCH bpf-next v11 1/2] bpf: add new helper get_file_path for mapping a file descriptor to a pathname
Date: Wed, 4 Dec 2019 23:19:00 -0800 [thread overview]
Message-ID: <20191205071858.entnj2c27n44kwit@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <afe4deb020b781c76e9df8403a744f88a8725cd2.1575517685.git.ethercflow@gmail.com>
On Wed, Dec 04, 2019 at 11:20:35PM -0500, Wenbo Zhang wrote:
>
> +BPF_CALL_3(bpf_get_file_path, char *, dst, u32, size, int, fd)
> +{
> + struct file *f;
> + char *p;
> + int ret = -EBADF;
> +
> + /* Ensure we're in user context which is safe for the helper to
> + * run. This helper has no business in a kthread.
> + */
> + if (unlikely(in_interrupt() ||
> + current->flags & (PF_KTHREAD | PF_EXITING))) {
> + ret = -EPERM;
> + goto error;
> + }
> +
> + /* Use fget_raw instead of fget to support O_PATH, and it doesn't
> + * have any sleepable code, so it's ok to be here.
> + */
> + f = fget_raw(fd);
> + if (!f)
> + goto error;
> +
> + /* For unmountable pseudo filesystem, it seems to have no meaning
> + * to get their fake paths as they don't have path, and to be no
> + * way to validate this function pointer can be always safe to call
> + * in the current context.
> + */
> + if (f->f_path.dentry->d_op && f->f_path.dentry->d_op->d_dname) {
> + ret = -EINVAL;
> + fput(f);
> + goto error;
> + }
> +
> + /* After filter unmountable pseudo filesytem, d_path won't call
> + * dentry->d_op->d_name(), the normally path doesn't have any
> + * sleepable code, and despite it uses the current macro to get
> + * fs_struct (current->fs), we've already ensured we're in user
> + * context, so it's ok to be here.
> + */
> + p = d_path(&f->f_path, dst, size);
Above 'if's are not enough to make sure that it won't dead lock.
Allowing it in tracing_func_proto() means that it's available to kprobe too.
Hence deadlock is possible. Please see previous email thread.
This helper is safe in tracepoint+bpf only.
next prev parent reply other threads:[~2019-12-05 7:19 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-19 13:27 [PATCH bpf-next v10 0/2] bpf: adding get_file_path helper Wenbo Zhang
2019-11-19 13:27 ` [PATCH bpf-next v10 1/2] bpf: add new helper get_file_path for mapping a file descriptor to a pathname Wenbo Zhang
2019-11-23 3:18 ` Alexei Starovoitov
2019-11-23 4:43 ` Al Viro
2019-11-23 4:51 ` Al Viro
2019-11-23 5:19 ` Alexei Starovoitov
2019-11-23 5:35 ` Al Viro
2019-11-23 6:04 ` Alexei Starovoitov
2019-12-13 19:51 ` Brendan Gregg
2019-12-05 4:20 ` [PATCH bpf-next v11 0/2] bpf: adding get_file_path helper Wenbo Zhang
2019-12-05 4:20 ` [PATCH bpf-next v11 1/2] bpf: add new helper get_file_path for mapping a file descriptor to a pathname Wenbo Zhang
2019-12-05 7:19 ` Alexei Starovoitov [this message]
2019-12-05 9:47 ` Wenbo Zhang
2019-12-15 4:01 ` [PATCH bpf-next v12 0/2] bpf: adding get_file_path helper Wenbo Zhang
2019-12-15 4:01 ` [PATCH bpf-next v12 1/2] bpf: add new helper get_file_path for mapping a file descriptor to a pathname Wenbo Zhang
2019-12-15 16:05 ` Yonghong Song
2019-12-17 6:26 ` Wenbo Zhang
2019-12-17 6:33 ` Yonghong Song
2019-12-15 16:10 ` Yonghong Song
2019-12-17 6:27 ` Wenbo Zhang
2019-12-16 22:09 ` Brendan Gregg
2019-12-17 4:05 ` Wenbo Zhang
2019-12-17 9:47 ` [PATCH bpf-next v13 0/2] bpf: adding get_fd_path helper Wenbo Zhang
2019-12-17 9:47 ` [PATCH bpf-next v13 1/2] bpf: add new helper get_fd_path for mapping a file descriptor to a pathname Wenbo Zhang
2019-12-17 16:29 ` Yonghong Song
2019-12-17 19:39 ` Daniel Borkmann
2019-12-18 0:11 ` Wenbo Zhang
2019-12-18 0:06 ` Wenbo Zhang
2019-12-18 0:56 ` [PATCH bpf-next v14 0/2] bpf: adding get_fd_path helper Wenbo Zhang
2019-12-18 0:56 ` [PATCH bpf-next v14 1/2] bpf: add new helper get_fd_path for mapping a file descriptor to a pathname Wenbo Zhang
2019-12-18 3:27 ` Yonghong Song
2019-12-19 16:14 ` Daniel Borkmann
2019-12-20 3:35 ` Wenbo Zhang
2020-01-16 8:59 ` Jiri Olsa
2020-02-10 4:43 ` Brendan Gregg
2020-02-11 0:01 ` Daniel Borkmann
2020-02-12 15:21 ` Jiri Olsa
2020-06-01 14:17 ` Wenbo Zhang
2020-06-01 16:38 ` Alexei Starovoitov
2020-06-02 3:04 ` Wenbo Zhang
2020-06-02 8:14 ` Jiri Olsa
2019-12-18 0:56 ` [PATCH bpf-next v14 2/2] selftests/bpf: test for bpf_get_fd_path() from tracepoint Wenbo Zhang
2019-12-18 3:27 ` Yonghong Song
2019-12-17 9:47 ` [PATCH bpf-next v13 " Wenbo Zhang
2019-12-17 16:32 ` Yonghong Song
2019-12-15 4:01 ` [PATCH bpf-next v12 2/2] selftests/bpf: test for bpf_get_file_path() " Wenbo Zhang
2019-12-15 16:24 ` Yonghong Song
2019-12-17 4:01 ` Wenbo Zhang
2019-12-17 4:13 ` Yonghong Song
2019-12-17 9:44 ` Wenbo Zhang
2019-12-05 4:20 ` [PATCH bpf-next v11 " Wenbo Zhang
2019-11-19 13:27 ` [PATCH bpf-next v10 " Wenbo Zhang
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20191205071858.entnj2c27n44kwit@ast-mbp.dhcp.thefacebook.com \
--to=alexei.starovoitov@gmail.com \
--cc=andrii.nakryiko@gmail.com \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=ethercflow@gmail.com \
--cc=netdev@vger.kernel.org \
--cc=yhs@fb.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).