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Date: Fri, 18 Oct 2019 18:20:08 +0000
From: Yonghong Song <yhs@...com>
To: Wenbo Zhang <ethercflow@...il.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC: "daniel@...earbox.net" <daniel@...earbox.net>
Subject: Re: [PATCH bpf-next] bpf: add new helper fd2path for mapping a file
descriptor to a pathname
On 10/18/19 3:47 AM, 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.
I commented on previous version of the patch.
Could you add version number (this is v2) to the patch set
when you submit next time (which will be v3).
>
> Signed-off-by: Wenbo Zhang <ethercflow@...il.com>
> ---
> include/linux/bpf.h | 1 +
> include/uapi/linux/bpf.h | 12 ++++++++++-
> kernel/bpf/core.c | 1 +
> kernel/bpf/helpers.c | 39 ++++++++++++++++++++++++++++++++++
> kernel/trace/bpf_trace.c | 2 ++
> tools/include/uapi/linux/bpf.h | 12 ++++++++++-
> 6 files changed, 65 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 2c2c29b49845..d73314a7e674 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1082,6 +1082,7 @@ extern const struct bpf_func_proto bpf_get_local_storage_proto;
> extern const struct bpf_func_proto bpf_strtol_proto;
> extern const struct bpf_func_proto bpf_strtoul_proto;
> extern const struct bpf_func_proto bpf_tcp_sock_proto;
> +extern const struct bpf_func_proto bpf_fd2path_proto;
>
> /* Shared helpers among cBPF and eBPF. */
> void bpf_user_rnd_init_once(void);
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 4af8b0819a32..fdb37740951f 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2773,6 +2773,15 @@ union bpf_attr {
> *
> * This helper is similar to **bpf_perf_event_output**\ () but
> * restricted to raw_tracepoint bpf programs.
> + *
> + * int bpf_fd2path(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*. The **path** also support pseudo filesystems
> + * (whether or not it can be mounted). The *size* must be strictly
> + * positive. On success, the helper makes sure that the *path* is
> + * NUL-terminated. On failure, it is filled with zeroes.
> * Return
> * 0 on success, or a negative error in case of failure.
> */
> @@ -2888,7 +2897,8 @@ union bpf_attr {
> FN(sk_storage_delete), \
> FN(send_signal), \
> FN(tcp_gen_syncookie), \
> - FN(skb_output),
> + FN(skb_output), \
> + FN(fd2path),
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> * function eBPF program intends to call
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 673f5d40a93e..6b44ed804280 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2079,6 +2079,7 @@ const struct bpf_func_proto bpf_get_current_uid_gid_proto __weak;
> const struct bpf_func_proto bpf_get_current_comm_proto __weak;
> const struct bpf_func_proto bpf_get_current_cgroup_id_proto __weak;
> const struct bpf_func_proto bpf_get_local_storage_proto __weak;
> +const struct bpf_func_proto bpf_fd2path_proto __weak;
>
> const struct bpf_func_proto * __weak bpf_get_trace_printk_proto(void)
> {
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 5e28718928ca..0832536c7ddb 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -487,3 +487,42 @@ const struct bpf_func_proto bpf_strtoul_proto = {
> .arg4_type = ARG_PTR_TO_LONG,
> };
> #endif
> +
> +BPF_CALL_3(bpf_fd2path, char *, dst, u32, size, int, fd)
> +{
> + struct fd f;
> + int ret;
> + char *p;
> +
> + ret = security_locked_down(LOCKDOWN_BPF_READ);
> + if (ret < 0)
> + goto out;
> +
> + f = fdget_raw(fd);
> + if (!f.file)
> + goto out;
> +
> + p = d_path(&f.file->f_path, dst, size);
> + if (IS_ERR_OR_NULL(p))
> + ret = PTR_ERR(p);
> + else {
> + ret = strlen(p);
> + memmove(dst, p, ret);
> + dst[ret] = 0;
> + }
> +
> + if (unlikely(ret < 0))
> +out:
> + memset(dst, '0', size);
> +
> + return ret;
> +}
> +
> +const struct bpf_func_proto bpf_fd2path_proto = {
> + .func = bpf_fd2path,
> + .gpl_only = true,
> + .ret_type = RET_INTEGER,
> + .arg1_type = ARG_PTR_TO_UNINIT_MEM,
> + .arg2_type = ARG_CONST_SIZE,
> + .arg3_type = ARG_ANYTHING,
> +};
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 52f7e9d8c29b..23cc3a955e59 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -735,6 +735,8 @@ tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> #endif
> case BPF_FUNC_send_signal:
> return &bpf_send_signal_proto;
> + case BPF_FUNC_fd2path:
> + return &bpf_fd2path_proto;
> default:
> return NULL;
> }
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 4af8b0819a32..fdb37740951f 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -2773,6 +2773,15 @@ union bpf_attr {
> *
> * This helper is similar to **bpf_perf_event_output**\ () but
> * restricted to raw_tracepoint bpf programs.
> + *
> + * int bpf_fd2path(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*. The **path** also support pseudo filesystems
> + * (whether or not it can be mounted). The *size* must be strictly
> + * positive. On success, the helper makes sure that the *path* is
> + * NUL-terminated. On failure, it is filled with zeroes.
> * Return
> * 0 on success, or a negative error in case of failure.
> */
> @@ -2888,7 +2897,8 @@ union bpf_attr {
> FN(sk_storage_delete), \
> FN(send_signal), \
> FN(tcp_gen_syncookie), \
> - FN(skb_output),
> + FN(skb_output), \
> + FN(fd2path),
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> * function eBPF program intends to call
>
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