[PATCH] bpf: Prevent double bpf_prog_put call from bpf_tracing_prog_attach

[Jiri Olsa]

The bpf_tracing_prog_attach error path calls bpf_prog_put
on prog, which causes refcount underflow when it's called
from link_create function.

  link_create
    prog = bpf_prog_get              <-- get
    ...
    tracing_bpf_link_attach(prog..
      bpf_tracing_prog_attach(prog..
        out_put_prog:
          bpf_prog_put(prog);        <-- put

    if (ret < 0)
      bpf_prog_put(prog);            <-- put

Removing bpf_prog_put call from bpf_tracing_prog_attach
and making sure its callers call it instead.

Signed-off-by: Jiri Olsa <jo...@kernel.org>
---
 kernel/bpf/syscall.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index c3bb03c8371f..e5999d86c76e 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2712,7 +2712,6 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
 out_put_prog:
        if (tgt_prog_fd && tgt_prog)
                bpf_prog_put(tgt_prog);
-       bpf_prog_put(prog);
        return err;
 }
 
@@ -2825,7 +2824,10 @@ static int bpf_raw_tracepoint_open(const union bpf_attr 
*attr)
                        tp_name = prog->aux->attach_func_name;
                        break;
                }
-               return bpf_tracing_prog_attach(prog, 0, 0);
+               err = bpf_tracing_prog_attach(prog, 0, 0);
+               if (err >= 0)
+                       return err;
+               goto out_put_prog;
        case BPF_PROG_TYPE_RAW_TRACEPOINT:
        case BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE:
                if (strncpy_from_user(buf,
-- 
2.26.2