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Date:   Tue, 12 Mar 2019 05:42:05 +0000
From:   Song Liu <songliubraving@...com>
To:     Yonghong Song <yhs@...com>
CC:     Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf] selftests/bpf: fix segfault of test_progs when prog
 loading failed



> On Mar 11, 2019, at 10:21 PM, Yonghong Song <yhs@...com> wrote:
> 
> The test_progs subtests, test_spin_lock() and test_map_lock(),
> requires BTF present to run successfully.
> Currently, when BTF failed to load, test_progs will segfault,
>  $ ./test_progs
>  ...
>  12: (bf) r1 = r8
>  13: (85) call bpf_spin_lock#93
>  map 'hash_map' has to have BTF in order to use bpf_spin_lock
> 
>  libbpf: -- END LOG --
>  libbpf: failed to load program 'map_lock_demo'
>  libbpf: failed to load object './test_map_lock.o'
>  test_map_lock:bpf_prog_load errno 13
>  Segmentation fault
> 
> The segfault is caused by uninitialized variable "obj", which
> is used in bpf_object__close(obj), when bpf prog failed to load.
> 
> Initializing variable "obj" to NULL in two occasions fixed the problem.
>  $ ./test_progs
>  ...
>  Summary: 219 PASSED, 2 FAILED
> 
> Fixes: b4d4556c3266 ("selftests/bpf: add bpf_spin_lock verifier tests")
> Fixes: ba72a7b4badb ("selftests/bpf: test for BPF_F_LOCK")
> Reported-by: Daniel Borkmann <daniel@...earbox.net>
> Signed-off-by: Yonghong Song <yhs@...com>

Acked-by: Song Liu <songliubraving@...com>

> ---
> tools/testing/selftests/bpf/prog_tests/map_lock.c | 2 +-
> tools/testing/selftests/bpf/prog_tests/spinlock.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/map_lock.c b/tools/testing/selftests/bpf/prog_tests/map_lock.c
> index 90f8a206340a..ee99368c595c 100644
> --- a/tools/testing/selftests/bpf/prog_tests/map_lock.c
> +++ b/tools/testing/selftests/bpf/prog_tests/map_lock.c
> @@ -37,7 +37,7 @@ void test_map_lock(void)
> 	const char *file = "./test_map_lock.o";
> 	int prog_fd, map_fd[2], vars[17] = {};
> 	pthread_t thread_id[6];
> -	struct bpf_object *obj;
> +	struct bpf_object *obj = NULL;
> 	int err = 0, key = 0, i;
> 	void *ret;
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/spinlock.c b/tools/testing/selftests/bpf/prog_tests/spinlock.c
> index 9a573a9675d7..114ebe6a438e 100644
> --- a/tools/testing/selftests/bpf/prog_tests/spinlock.c
> +++ b/tools/testing/selftests/bpf/prog_tests/spinlock.c
> @@ -5,7 +5,7 @@ void test_spinlock(void)
> {
> 	const char *file = "./test_spin_lock.o";
> 	pthread_t thread_id[4];
> -	struct bpf_object *obj;
> +	struct bpf_object *obj = NULL;
> 	int prog_fd;
> 	int err = 0, i;
> 	void *ret;
> -- 
> 2.17.1
> 

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