On Wed, May 29, 2019 at 1:30 AM Michal Rostecki <mrostecki@xxxxxxxxxxxx> wrote:
>
> Function load_sk_storage_btf expects that libbpf__probe_raw_btf is
> returning a btf descriptor, but before this change it was returning
> an information about whether the probe was successful (0 or 1).
> load_sk_storage_btf was using that value as an argument to the close
> function, which was resulting in closing stdout and thus terminating the
> process which used that dunction.
>
> That bug was visible in bpftool. `bpftool feature` subcommand was always
> exiting too early (because of closed stdout) and it didn't display all
> requested probes. `bpftool -j feature` or `bpftool -p feature` were not
> returning a valid json object.
>
Thanks for the fix!
> Fixes: d7c4b3980c18 ("libbpf: detect supported kernel BTF features and sanitize BTF")
> Signed-off-by: Michal Rostecki <mrostecki@xxxxxxxxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 36 +++++++++++++++++++++--------------
> tools/lib/bpf/libbpf_probes.c | 7 +------
> 2 files changed, 23 insertions(+), 20 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 197b574406b3..bc2dca36bced 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -1645,15 +1645,19 @@ static int bpf_object__probe_btf_func(struct bpf_object *obj)
> /* FUNC x */ /* [3] */
> BTF_TYPE_ENC(5, BTF_INFO_ENC(BTF_KIND_FUNC, 0, 0), 2),
> };
> - int res;
> + int btf_fd;
> + int ret;
>
> - res = libbpf__probe_raw_btf((char *)types, sizeof(types),
> - strs, sizeof(strs));
> - if (res < 0)
> - return res;
> - if (res > 0)
> + btf_fd = libbpf__probe_raw_btf((char *)types, sizeof(types),
> + strs, sizeof(strs));
> + if (btf_fd < 0)
> + ret = 0;
> + else {
> + ret = 1;
This whole ret variable seems unnecessary. Also if btf_fd is invalid,
we probably shouldn't close it. So just this should work:
btf_fd = libbpf__probe_raw_btf(...);
if (btf_fd >= 0) {
obj->caps.btf_func = 1;
close(btf_fd);
}
return btf_fd >= 0;
> obj->caps.btf_func = 1;
> - return 0;
> + }
> + close(btf_fd);
> + return ret;
> }
>
> static int bpf_object__probe_btf_datasec(struct bpf_object *obj)
> @@ -1670,15 +1674,19 @@ static int bpf_object__probe_btf_datasec(struct bpf_object *obj)
> BTF_TYPE_ENC(3, BTF_INFO_ENC(BTF_KIND_DATASEC, 0, 1), 4),
> BTF_VAR_SECINFO_ENC(2, 0, 4),
> };
> - int res;
> + int btf_fd;
> + int ret;
>
> - res = libbpf__probe_raw_btf((char *)types, sizeof(types),
> - strs, sizeof(strs));
> - if (res < 0)
> - return res;
> - if (res > 0)
> + btf_fd = libbpf__probe_raw_btf((char *)types, sizeof(types),
> + strs, sizeof(strs));
> + if (btf_fd < 0)
> + ret = 0;
> + else {
> + ret = 1;
> obj->caps.btf_datasec = 1;
> - return 0;
> + }
> + close(btf_fd);
Same as above.
> + return ret;
> }
>
> static int
> diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
> index 5e2aa83f637a..2c2828345514 100644
> --- a/tools/lib/bpf/libbpf_probes.c
> +++ b/tools/lib/bpf/libbpf_probes.c
> @@ -157,14 +157,9 @@ int libbpf__probe_raw_btf(const char *raw_types, size_t types_len,
I'm wondering if it's better to rename this function to something like
libbpf__load_raw_btf? probe (at least to me) implies true/false
result, so feels like it might be easily misused.
> memcpy(raw_btf + hdr.hdr_len + hdr.type_len, str_sec, hdr.str_len);
>
> btf_fd = bpf_load_btf(raw_btf, btf_len, NULL, 0, false);
> - if (btf_fd < 0) {
> - free(raw_btf);
> - return 0;
> - }
>
> - close(btf_fd);
> free(raw_btf);
> - return 1;
> + return btf_fd;
> }
>
> static int load_sk_storage_btf(void)
> --
> 2.21.0
>
