BPF Archive on lore.kernel.org
 help / color / Atom feed
From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Wenbo Zhang <ethercflow@gmail.com>
Cc: bpf@vger.kernel.org, ast@kernel.org.com, daniel@iogearbox.net,
	yhs@fb.com, andrii.nakryiko@gmail.com, netdev@vger.kernel.org,
	viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH bpf-next v10 1/2] bpf: add new helper get_file_path for mapping a file descriptor to a pathname
Date: Fri, 22 Nov 2019 19:18:28 -0800
Message-ID: <20191123031826.j2dj7mzto57ml6pr@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <e8b1281b7405eb4b6c1f094169e6efd2c8cc95da.1574162990.git.ethercflow@gmail.com>

On Tue, Nov 19, 2019 at 08:27:37AM -0500, Wenbo Zhang wrote:
> When people want to identify which file system files are being opened,
> read, and written to, they can use this helper with file descriptor as
> input to achieve this goal. Other pseudo filesystems are also supported.
> 
> This requirement is mainly discussed here:
> 
>   https://github.com/iovisor/bcc/issues/237
> 
> v9->v10: addressed Andrii's feedback
> - send this patch together with the patch selftests as one patch series
> 
> v8->v9:
> - format helper description
> 
> v7->v8: addressed Alexei's feedback
> - use fget_raw instead of fdget_raw, as fdget_raw is only used inside fs/
> - ensure we're in user context which is safe fot the help to run
> - filter unmountable pseudo filesystem, because they don't have real path
> - supplement the description of this helper function
> 
> v6->v7:
> - fix missing signed-off-by line
> 
> v5->v6: addressed Andrii's feedback
> - avoid unnecessary goto end by having two explicit returns
> 
> v4->v5: addressed Andrii and Daniel's feedback
> - rename bpf_fd2path to bpf_get_file_path to be consistent with other
> helper's names
> - when fdget_raw fails, set ret to -EBADF instead of -EINVAL
> - remove fdput from fdget_raw's error path
> - use IS_ERR instead of IS_ERR_OR_NULL as d_path ether returns a pointer
> into the buffer or an error code if the path was too long
> - modify the normal path's return value to return copied string length
> including NUL
> - update this helper description's Return bits.
> 
> v3->v4: addressed Daniel's feedback
> - fix missing fdput()
> - move fd2path from kernel/bpf/trace.c to kernel/trace/bpf_trace.c
> - move fd2path's test code to another patch
> - add comment to explain why use fdget_raw instead of fdget
> 
> v2->v3: addressed Yonghong's feedback
> - remove unnecessary LOCKDOWN_BPF_READ
> - refactor error handling section for enhanced readability
> - provide a test case in tools/testing/selftests/bpf
> 
> v1->v2: addressed Daniel's feedback
> - fix backward compatibility
> - add this helper description
> - fix signed-off name
> 
> Signed-off-by: Wenbo Zhang <ethercflow@gmail.com>
...
> +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)))
> +		return -EPERM;
> +
> +	/* 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)
> +		return -EINVAL;
> +
> +	/* 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);
> +	if (IS_ERR(p)) {
> +		ret = PTR_ERR(p);
> +		fput(f);
> +		goto error;
> +	}
> +
> +	ret = strlen(p);
> +	memmove(dst, p, ret);
> +	dst[ret++] = '\0';
> +	fput(f);
> +	return ret;
> +
> +error:
> +	memset(dst, '0', size);
> +	return ret;
> +}

Al,

could you please review about code whether it's doing enough checks to be
called safely from preempt_disabled region?

It's been under review for many weeks and looks good from bpf pov. Essentially
tracing folks need easy way to convert FD to full path name. This feature
request first came in 2015.

Thanks!


  reply index

Thread overview: 48+ 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 [this message]
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
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
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=20191123031826.j2dj7mzto57ml6pr@ast-mbp.dhcp.thefacebook.com \
    --to=alexei.starovoitov@gmail.com \
    --cc=andrii.nakryiko@gmail.com \
    --cc=ast@kernel.org.com \
    --cc=bpf@vger.kernel.org \
    --cc=daniel@iogearbox.net \
    --cc=ethercflow@gmail.com \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=netdev@vger.kernel.org \
    --cc=viro@zeniv.linux.org.uk \
    --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

BPF Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/bpf/0 bpf/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 bpf bpf/ https://lore.kernel.org/bpf \
		bpf@vger.kernel.org
	public-inbox-index bpf

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.bpf


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git