Patch "bpftool: Fix missing pids during link show" has been added to the 6.1-stable tree

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This is a note to let you know that I've just added the patch titled

    bpftool: Fix missing pids during link show

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     bpftool-fix-missing-pids-during-link-show.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 566ef89b5748809f780e93a80125f2dc2be1541e
Author: Yonghong Song <yonghong.song@xxxxxxxxx>
Date:   Mon Mar 11 19:32:49 2024 -0700

    bpftool: Fix missing pids during link show
    
    [ Upstream commit fe879bb42f8a6513ed18e9d22efb99cb35590201 ]
    
    Current 'bpftool link' command does not show pids, e.g.,
      $ tools/build/bpftool/bpftool link
      ...
      4: tracing  prog 23
            prog_type lsm  attach_type lsm_mac
            target_obj_id 1  target_btf_id 31320
    
    Hack the following change to enable normal libbpf debug output,
      --- a/tools/bpf/bpftool/pids.c
      +++ b/tools/bpf/bpftool/pids.c
      @@ -121,9 +121,9 @@ int build_obj_refs_table(struct hashmap **map, enum bpf_obj_type type)
              /* we don't want output polluted with libbpf errors if bpf_iter is not
               * supported
               */
      -       default_print = libbpf_set_print(libbpf_print_none);
      +       /* default_print = libbpf_set_print(libbpf_print_none); */
              err = pid_iter_bpf__load(skel);
      -       libbpf_set_print(default_print);
      +       /* libbpf_set_print(default_print); */
    
    Rerun the above bpftool command:
      $ tools/build/bpftool/bpftool link
      libbpf: prog 'iter': BPF program load failed: Permission denied
      libbpf: prog 'iter': -- BEGIN PROG LOAD LOG --
      0: R1=ctx() R10=fp0
      ; struct task_struct *task = ctx->task; @ pid_iter.bpf.c:69
      0: (79) r6 = *(u64 *)(r1 +8)          ; R1=ctx() R6_w=ptr_or_null_task_struct(id=1)
      ; struct file *file = ctx->file; @ pid_iter.bpf.c:68
      ...
      ; struct bpf_link *link = (struct bpf_link *) file->private_data; @ pid_iter.bpf.c:103
      80: (79) r3 = *(u64 *)(r8 +432)       ; R3_w=scalar() R8=ptr_file()
      ; if (link->type == bpf_core_enum_value(enum bpf_link_type___local, @ pid_iter.bpf.c:105
      81: (61) r1 = *(u32 *)(r3 +12)
      R3 invalid mem access 'scalar'
      processed 39 insns (limit 1000000) max_states_per_insn 0 total_states 3 peak_states 3 mark_read 2
      -- END PROG LOAD LOG --
      libbpf: prog 'iter': failed to load: -13
      ...
    
    The 'file->private_data' returns a 'void' type and this caused subsequent 'link->type'
    (insn #81) failed in verification.
    
    To fix the issue, restore the previous BPF_CORE_READ so old kernels can also work.
    With this patch, the 'bpftool link' runs successfully with 'pids'.
      $ tools/build/bpftool/bpftool link
      ...
      4: tracing  prog 23
            prog_type lsm  attach_type lsm_mac
            target_obj_id 1  target_btf_id 31320
            pids systemd(1)
    
    Fixes: 44ba7b30e84f ("bpftool: Use a local copy of BPF_LINK_TYPE_PERF_EVENT in pid_iter.bpf.c")
    Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
    Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
    Tested-by: Quentin Monnet <quentin@xxxxxxxxxxxxx>
    Reviewed-by: Quentin Monnet <quentin@xxxxxxxxxxxxx>
    Link: https://lore.kernel.org/bpf/20240312023249.3776718-1-yonghong.song@xxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
index 26004f0c5a6ae..7bdbcac3cf628 100644
--- a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
+++ b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
@@ -102,8 +102,8 @@ int iter(struct bpf_iter__task_file *ctx)
 				       BPF_LINK_TYPE_PERF_EVENT___local)) {
 		struct bpf_link *link = (struct bpf_link *) file->private_data;
 
-		if (link->type == bpf_core_enum_value(enum bpf_link_type___local,
-						      BPF_LINK_TYPE_PERF_EVENT___local)) {
+		if (BPF_CORE_READ(link, type) == bpf_core_enum_value(enum bpf_link_type___local,
+								     BPF_LINK_TYPE_PERF_EVENT___local)) {
 			e.has_bpf_cookie = true;
 			e.bpf_cookie = get_bpf_cookie(link);
 		}




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