Re: [PATCH bpf-next v1 1/3] bpf: Add bpf_file_d_path helper

On Thu, Jul 18, 2024 at 4:53 AM Lin Yikai yikai.lin@vivo.com wrote:

Add the "bpf_file_d_path" helper function to retrieve the path from a struct file object. But there is no need to include vmlinux.h or reference the definition of struct file.

Additionally, update the bpf.h tools uapi header.

Signed-off-by: Lin Yikai yikai.lin@vivo.com

include/uapi/linux/bpf.h | 20 ++++++++++++++++++++ kernel/trace/bpf_trace.c | 34 ++++++++++++++++++++++++++++++++++ tools/include/uapi/linux/bpf.h | 20 ++++++++++++++++++++ 3 files changed, 74 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 35bcf52dbc65..7e5cec61a877 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -5792,6 +5792,25 @@ union bpf_attr {

•         0 on success.
  

•         **-ENOENT** if the bpf_local_storage cannot be found.
  

• • long bpf_file_d_path(void *file, char *dst, u32 size)

• • Description
    

• •         Return full path for the given *file* object.
    

• •         In order to solve issues where certain eBPF programs can not include
    

• •         the definition of struct file or vmlinux.h
    

• •         due to their complexity and conflicts on some operating system,
    

• •         the variable *file* here is declared as type void*
    

• •         instead of the traditional struct file*.
    

• •         It will be forcibly converted into type struct file* later.
    

• •         If the path is larger than *size*, then only *size*
    

• •         bytes will be copied to *dst*
    

• • Return
    

• •         On success, the strictly positive length of the string,
    

• •         including the trailing NULL character. On error, a negative
    

• •         value.
    

  */

#define ___BPF_FUNC_MAPPER(FN, ctx...) \ FN(unspec, 0, ##ctx) \ @@ -6006,6 +6025,7 @@ union bpf_attr { FN(user_ringbuf_drain, 209, ##ctx) \ FN(cgrp_storage_get, 210, ##ctx) \ FN(cgrp_storage_delete, 211, ##ctx) \

•   FN(file_d_path, 212, ##ctx)                     \
    /* */
  
  

/* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index cd098846e251..70fde7f20e97 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -1257,6 +1257,38 @@ static const struct bpf_func_proto bpf_get_func_arg_cnt_proto = { .arg1_type = ARG_PTR_TO_CTX, };

+BPF_CALL_3(bpf_file_d_path, void *, file, char*, dst, u32, size) +{

•   long len;
  

•   struct file copy;
  

•   char *ptr;
  

•   if (!size)
  

•           return 0;
  

•   len = copy_from_kernel_nofault(&copy, (struct file *)file, sizeof(struct file));
  

•   if (len < 0)
  

•           return len;
  

•   ptr = d_path(&(copy.f_path), dst, size);
  

•   if (IS_ERR(ptr)) {
  

•           len = PTR_ERR(ptr);
  

•   } else {
  

•           len = dst + size - ptr;
  

•           memmove(dst, ptr, len);
  

•   }
  

•   return len;
  

+}

+const struct bpf_func_proto bpf_file_d_path_proto = {

•   .func           = bpf_file_d_path,
  

•   .gpl_only       = false,
  

•   .ret_type       = RET_INTEGER,
  

•   .arg1_type      = ARG_ANYTHING,
  

you can't just accept any random value as `struct file *`, this is a complete no-go. It will have to accept some sort of PTR_TRUSTED argument, be added as kfunc, etc, etc. We had earlier discussion around this, I don't remember all the details, but this is definitely not the way forward.

•   .arg2_type      = ARG_PTR_TO_MEM,
  

•   .arg3_type      = ARG_CONST_SIZE_OR_ZERO,
  

+};

#ifdef CONFIG_KEYS __bpf_kfunc_start_defs();

@@ -1629,6 +1661,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) return &bpf_find_vma_proto; case BPF_FUNC_trace_vprintk: return bpf_get_trace_vprintk_proto();

•   case BPF_FUNC_file_d_path:
  

•           return &bpf_file_d_path_proto;
    default:
            return bpf_base_func_proto(func_id, prog);
    }
  

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 35bcf52dbc65..7e5cec61a877 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -5792,6 +5792,25 @@ union bpf_attr {

•         0 on success.
  

•         **-ENOENT** if the bpf_local_storage cannot be found.
  

• • long bpf_file_d_path(void *file, char *dst, u32 size)

• • Description
    

• •         Return full path for the given *file* object.
    

• •         In order to solve issues where certain eBPF programs can not include
    

• •         the definition of struct file or vmlinux.h
    

• •         due to their complexity and conflicts on some operating system,
    

• •         the variable *file* here is declared as type void*
    

• •         instead of the traditional struct file*.
    

• •         It will be forcibly converted into type struct file* later.
    

• •         If the path is larger than *size*, then only *size*
    

• •         bytes will be copied to *dst*
    

• • Return
    

• •         On success, the strictly positive length of the string,
    

• •         including the trailing NULL character. On error, a negative
    

• •         value.
    

  */

#define ___BPF_FUNC_MAPPER(FN, ctx...) \ FN(unspec, 0, ##ctx) \ @@ -6006,6 +6025,7 @@ union bpf_attr { FN(user_ringbuf_drain, 209, ##ctx) \ FN(cgrp_storage_get, 210, ##ctx) \ FN(cgrp_storage_delete, 211, ##ctx) \

•   FN(file_d_path, 212, ##ctx)                     \
    /* */
  
  

/* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't

2.34.1