From: Yonghong Song Date: Tue, 12 Jun 2018 05:35:48 +0000 (-0700) Subject: tools/bpftool: fix a bug in bpftool perf X-Git-Tag: v4.18-rc2~28^2~25^2~6 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=73df93c57c0b18195a2fe5429747e00018b3e863;p=users%2Fhch%2Fuuid.git 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 Signed-off-by: Yonghong Song Reviewed-by: Jakub Kicinski Signed-off-by: Daniel Borkmann --- 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; }