[PATCH 6.6 129/744] bpftool: Fix missing pids during link show

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6.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Yonghong Song <yonghong.song@xxxxxxxxx>

[ 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>
---
 tools/bpf/bpftool/skeleton/pid_iter.bpf.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

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);
 		}
-- 
2.43.0







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