netdev - [PATCH] bpf: Prevent double bpf_prog_put call from bpf_tracing_prog

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Message-Id: <20210111191650.1241578-1-jolsa@kernel.org>
Date:   Mon, 11 Jan 2021 20:16:50 +0100
From:   Jiri Olsa <jolsa@...nel.org>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: [PATCH] bpf: Prevent double bpf_prog_put call from bpf_tracing_prog_attach

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 <jolsa@...nel.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