From: Yonghong Song <yhs@fb.com>
To: Wenbo Zhang <ethercflow@gmail.com>,
"bpf@vger.kernel.org" <bpf@vger.kernel.org>
Cc: "ast@kernel.org" <ast@kernel.org>,
"daniel@iogearbox.net" <daniel@iogearbox.net>,
"andrii.nakryiko@gmail.com" <andrii.nakryiko@gmail.com>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: Re: [PATCH bpf-next v12 1/2] bpf: add new helper get_file_path for mapping a file descriptor to a pathname
Date: Sun, 15 Dec 2019 16:10:10 +0000 [thread overview]
Message-ID: <aa4bf1b3-0411-1a04-6156-3fb97add1f2c@fb.com> (raw)
In-Reply-To: <0117d6e17ba8b3b1273e5a964f87a71c1b2d8741.1576381512.git.ethercflow@gmail.com>
On 12/14/19 8:01 PM, 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
>
> v11->v12: addressed Alexei's feedback
> - only allow tracepoints to make sure it won't dead lock
>
> v10->v11: addressed Al and Alexei's feedback
> - fix missing fput()
>
> 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>
> ---
> include/uapi/linux/bpf.h | 29 +++++++++++++-
> kernel/trace/bpf_trace.c | 70 ++++++++++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 29 +++++++++++++-
> 3 files changed, 126 insertions(+), 2 deletions(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index dbbcf0b02970..71d9705df120 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2821,6 +2821,32 @@ union bpf_attr {
> * Return
> * On success, the strictly positive length of the string, including
> * the trailing NUL character. On error, a negative value.
> + *
> + * int bpf_get_file_path(char *path, u32 size, int fd)
> + * Description
> + * Get **file** atrribute from the current task by *fd*, then call
> + * **d_path** to get it's absolute path and copy it as string into
> + * *path* of *size*. Notice the **path** don't support unmountable
> + * pseudo filesystems as they don't have path (eg: SOCKFS, PIPEFS).
> + * The *size* must be strictly positive. On success, the helper
> + * makes sure that the *path* is NUL-terminated, and the buffer
> + * could be:
> + * - a regular full path (include mountable fs eg: /proc, /sys)
> + * - a regular full path with "(deleted)" at the end.
> + * On failure, it is filled with zeroes.
> + * Return
> + * On success, returns the length of the copied string INCLUDING
> + * the trailing NUL.
> + *
> + * On failure, the returned value is one of the following:
> + *
> + * **-EPERM** if no permission to get the path (eg: in irq ctx).
> + *
> + * **-EBADF** if *fd* is invalid.
> + *
> + * **-EINVAL** if *fd* corresponds to a unmountable pseudo fs
> + *
> + * **-ENAMETOOLONG** if full path is longer than *size*
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -2938,7 +2964,8 @@ union bpf_attr {
> FN(probe_read_user), \
> FN(probe_read_kernel), \
> FN(probe_read_user_str), \
> - FN(probe_read_kernel_str),
> + FN(probe_read_kernel_str), \
> + FN(get_file_path),
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> * function eBPF program intends to call
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index e5ef4ae9edb5..db9c0ec46a5d 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -762,6 +762,72 @@ static const struct bpf_func_proto bpf_send_signal_proto = {
> .arg1_type = ARG_ANYTHING,
> };
>
> +BPF_CALL_3(bpf_get_file_path, char *, dst, u32, size, int, fd)
> +{
> + struct file *f;
> + char *p;
> + int ret = -EBADF;
please try to use reverse Christmas tree for declarations.
> +
> + /* 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);
> + 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;
> +}
> +
[...]
next prev parent reply other threads:[~2019-12-15 16:10 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
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 [this message]
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
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