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authorYonghong Song <yhs@fb.com>2018-06-11 22:35:48 -0700
committerDaniel Borkmann <daniel@iogearbox.net>2018-06-13 02:03:17 +0200
commit73df93c57c0b18195a2fe5429747e00018b3e863 (patch)
treed5f8d08b8f9b96a5241e182142f50e51d488230d /tools
parent5d902372ba5f416261c79123f02e49c664c7118f (diff)
downloadlinux-73df93c57c0b18195a2fe5429747e00018b3e863.tar.bz2
tools/bpftool: fix a bug in bpftool perf
Commit b04df400c302 ("tools/bpftool: add perf subcommand") introduced bpftool subcommand perf to query bpf program kuprobe and tracepoint attachments. The perf subcommand will first test whether bpf subcommand BPF_TASK_FD_QUERY is supported in kernel or not. It does it by opening a file with argv[0] and feeds the file descriptor and current task pid to the kernel for querying. Such an approach won't work if the argv[0] cannot be opened successfully in the current directory. This is especially true when bpftool is accessible through PATH env variable. The error below reflects the open failure for file argv[0] at home directory. [yhs@localhost ~]$ which bpftool /usr/local/sbin/bpftool [yhs@localhost ~]$ bpftool perf Error: perf_query_support: No such file or directory To fix the issue, let us open root directory ("/") which exists in every linux system. With the fix, the error message will correctly reflect the permission issue. [yhs@localhost ~]$ which bpftool /usr/local/sbin/bpftool [yhs@localhost ~]$ bpftool perf Error: perf_query_support: Operation not permitted HINT: non root or kernel doesn't support TASK_FD_QUERY Fixes: b04df400c302 ("tools/bpftool: add perf subcommand") Reported-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Yonghong Song <yhs@fb.com> Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Diffstat (limited to 'tools')
-rw-r--r--tools/bpf/bpftool/perf.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/tools/bpf/bpftool/perf.c b/tools/bpf/bpftool/perf.c
index ac6b1a12c9b7..b76b77dcfd1f 100644
--- a/tools/bpf/bpftool/perf.c
+++ b/tools/bpf/bpftool/perf.c
@@ -29,9 +29,10 @@ static bool has_perf_query_support(void)
if (perf_query_supported)
goto out;
- fd = open(bin_name, O_RDONLY);
+ fd = open("/", O_RDONLY);
if (fd < 0) {
- p_err("perf_query_support: %s", strerror(errno));
+ p_err("perf_query_support: cannot open directory \"/\" (%s)",
+ strerror(errno));
goto out;
}