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    Subject[PATCH 5.2 21/94] libbpf: fix erroneous multi-closing of BTF FD
    Date
    [ Upstream commit 5d01ab7bac467edfc530e6ccf953921def935c62 ]

    Libbpf stores associated BTF FD per each instance of bpf_program. When
    program is unloaded, that FD is closed. This is wrong, because leads to
    a race and possibly closing of unrelated files, if application
    simultaneously opens new files while bpf_programs are unloaded.

    It's also unnecessary, because struct btf "owns" that FD, and
    btf__free(), called from bpf_object__close() will close it. Thus the fix
    is to never have per-program BTF FD and fetch it from obj->btf, when
    necessary.

    Fixes: 2993e0515bb4 ("tools/bpf: add support to read .BTF.ext sections")
    Reported-by: Andrey Ignatov <rdna@fb.com>
    Signed-off-by: Andrii Nakryiko <andriin@fb.com>
    Signed-off-by: Alexei Starovoitov <ast@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    tools/lib/bpf/libbpf.c | 11 +++--------
    1 file changed, 3 insertions(+), 8 deletions(-)

    diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
    index 77e14d9954796..21355f6be2434 100644
    --- a/tools/lib/bpf/libbpf.c
    +++ b/tools/lib/bpf/libbpf.c
    @@ -178,7 +178,6 @@ struct bpf_program {
    bpf_program_clear_priv_t clear_priv;

    enum bpf_attach_type expected_attach_type;
    - int btf_fd;
    void *func_info;
    __u32 func_info_rec_size;
    __u32 func_info_cnt;
    @@ -305,7 +304,6 @@ void bpf_program__unload(struct bpf_program *prog)
    prog->instances.nr = -1;
    zfree(&prog->instances.fds);

    - zclose(prog->btf_fd);
    zfree(&prog->func_info);
    zfree(&prog->line_info);
    }
    @@ -382,7 +380,6 @@ bpf_program__init(void *data, size_t size, char *section_name, int idx,
    prog->instances.fds = NULL;
    prog->instances.nr = -1;
    prog->type = BPF_PROG_TYPE_UNSPEC;
    - prog->btf_fd = -1;

    return 0;
    errout:
    @@ -1888,9 +1885,6 @@ bpf_program_reloc_btf_ext(struct bpf_program *prog, struct bpf_object *obj,
    prog->line_info_rec_size = btf_ext__line_info_rec_size(obj->btf_ext);
    }

    - if (!insn_offset)
    - prog->btf_fd = btf__fd(obj->btf);
    -
    return 0;
    }

    @@ -2065,7 +2059,7 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
    char *cp, errmsg[STRERR_BUFSIZE];
    int log_buf_size = BPF_LOG_BUF_SIZE;
    char *log_buf;
    - int ret;
    + int btf_fd, ret;

    memset(&load_attr, 0, sizeof(struct bpf_load_program_attr));
    load_attr.prog_type = prog->type;
    @@ -2077,7 +2071,8 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
    load_attr.license = license;
    load_attr.kern_version = kern_version;
    load_attr.prog_ifindex = prog->prog_ifindex;
    - load_attr.prog_btf_fd = prog->btf_fd >= 0 ? prog->btf_fd : 0;
    + btf_fd = bpf_object__btf_fd(prog->obj);
    + load_attr.prog_btf_fd = btf_fd >= 0 ? btf_fd : 0;
    load_attr.func_info = prog->func_info;
    load_attr.func_info_rec_size = prog->func_info_rec_size;
    load_attr.func_info_cnt = prog->func_info_cnt;
    --
    2.20.1


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