Message ID | 20180612020108.125247-1-yhs@fb.com |
---|---|
State | Changes Requested, archived |
Delegated to: | BPF Maintainers |
Headers | show |
Series | [bpf,v2] tools/bpftool: fix a bug in bpftool perf | expand |
On Mon, 11 Jun 2018 19:01:08 -0700, Yonghong Song wrote: > 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> > --- > tools/bpf/bpftool/perf.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > Changelogs: > v1 -> v2: > . remove '\n' in the p_err format string in order to > have valid json output. > > diff --git a/tools/bpf/bpftool/perf.c b/tools/bpf/bpftool/perf.c > index ac6b1a12c9b7..239715aa6fb9 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); > - if (fd < 0) { > - p_err("perf_query_support: %s", strerror(errno)); > + fd = open("/", O_RDONLY); > + if (fd > 0) { Looking at this again, why change the comparison from less than to greater than 0? > + p_err("perf_query_support: cannot open directory \"/\" (%s)", > + strerror(errno)); > goto out; > } >
On 6/11/18 7:42 PM, Jakub Kicinski wrote: > On Mon, 11 Jun 2018 19:01:08 -0700, Yonghong Song wrote: >> 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> >> --- >> tools/bpf/bpftool/perf.c | 7 ++++--- >> 1 file changed, 4 insertions(+), 3 deletions(-) >> >> Changelogs: >> v1 -> v2: >> . remove '\n' in the p_err format string in order to >> have valid json output. >> >> diff --git a/tools/bpf/bpftool/perf.c b/tools/bpf/bpftool/perf.c >> index ac6b1a12c9b7..239715aa6fb9 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); >> - if (fd < 0) { >> - p_err("perf_query_support: %s", strerror(errno)); >> + fd = open("/", O_RDONLY); >> + if (fd > 0) { > > Looking at this again, why change the comparison from less than to > greater than 0? Totally my fault. I altered the condition to test p_err output since I cannot trigger it normally, but forgot to change it back. Will send yet another revision :-( >> + p_err("perf_query_support: cannot open directory \"/\" (%s)", >> + strerror(errno)); >> goto out; >> } >> >
diff --git a/tools/bpf/bpftool/perf.c b/tools/bpf/bpftool/perf.c index ac6b1a12c9b7..239715aa6fb9 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); - if (fd < 0) { - p_err("perf_query_support: %s", strerror(errno)); + fd = open("/", O_RDONLY); + if (fd > 0) { + p_err("perf_query_support: cannot open directory \"/\" (%s)", + strerror(errno)); goto out; }
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> --- tools/bpf/bpftool/perf.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) Changelogs: v1 -> v2: . remove '\n' in the p_err format string in order to have valid json output.