On Sun, Oct 8, 2023 at 10:51 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> On Thu, Oct 5, 2023 at 4:09 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
> >
> > Found by clang-tidy:
> > ```
> > bench/uprobe.c:98:3: warning: Use of memory after it is freed [clang-analyzer-unix.Malloc]
> > bench_uprobe_bpf__destroy(skel);
> > ```
> >
> > Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
>
> I'm ok with the change but I think it won't call
> bench_uprobe__teardown_bpf_skel() if the setup function
> returns a negative value. Maybe we also need to set the
> err in the default case of `switch (bench)` statement.
Yes, the analysis (I'll put it below) assumes that the err can be
positive yielding destroy being called twice, the second creating a
use-after-free. I think it is worth cleaning the code up and making
the analyzer's job easier.
Thanks,
Ian
```
bench/uprobe.c:98:3: warning: Use of memory after it is freed
[clang-analyzer-unix.Malloc]
bench_uprobe_bpf__destroy(skel);
^
tools/perf/bench/uprobe.c:197:9: note: Calling 'bench_uprobe'
return bench_uprobe(argc, argv, BENCH_UPROBE__TRACE_PRINTK);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tools/perf/bench/uprobe.c:150:6: note: 'bench' is not equal to
BENCH_UPROBE__BASELINE
if (bench != BENCH_UPROBE__BASELINE &&
bench_uprobe__setup_bpf_skel(bench) < 0)
^~~~~
tools/perf/bench/uprobe.c:150:6: note: Left side of '&&' is true
tools/perf/bench/uprobe.c:150:41: note: Calling 'bench_uprobe__setup_bpf_skel'
if (bench != BENCH_UPROBE__BASELINE &&
bench_uprobe__setup_bpf_skel(bench) < 0)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tools/perf/bench/uprobe.c:68:7: note: 'skel' is non-null
if (!skel) {
^~~~
tools/perf/bench/uprobe.c:68:2: note: Taking false branch
if (!skel) {
^
tools/perf/bench/uprobe.c:74:6: note: Assuming 'err' is not equal to 0
if (err) {
^~~
tools/perf/bench/uprobe.c:74:2: note: Taking true branch
if (err) {
^
tools/perf/bench/uprobe.c:76:3: note: Control jumps to line 91
goto cleanup;
^
tools/perf/bench/uprobe.c:91:2: note: Calling 'bench_uprobe_bpf__destroy'
bench_uprobe_bpf__destroy(skel);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tools/perf/util/bpf_skel/bench_uprobe.skel.h:44:6: note: Assuming
'obj' is non-null
if (!obj)
^~~~
tools/perf/util/bpf_skel/bench_uprobe.skel.h:44:2: note: Taking false branch
if (!obj)
^
tools/perf/util/bpf_skel/bench_uprobe.skel.h:46:6: note: Assuming
field 'skeleton' is null
if (obj->skeleton)
^~~~~~~~~~~~~
tools/perf/util/bpf_skel/bench_uprobe.skel.h:46:2: note: Taking false branch
if (obj->skeleton)
^
tools/perf/util/bpf_skel/bench_uprobe.skel.h:48:2: note: Memory is released
free(obj);
^~~~~~~~~
tools/perf/bench/uprobe.c:91:2: note: Returning; memory was released
via 1st parameter
bench_uprobe_bpf__destroy(skel);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tools/perf/bench/uprobe.c:150:41: note: Returning; memory was released
if (bench != BENCH_UPROBE__BASELINE &&
bench_uprobe__setup_bpf_skel(bench) < 0)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tools/perf/bench/uprobe.c:150:41: note: Assuming the condition is false
if (bench != BENCH_UPROBE__BASELINE &&
bench_uprobe__setup_bpf_skel(bench) < 0)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tools/perf/bench/uprobe.c:150:2: note: Taking false branch
if (bench != BENCH_UPROBE__BASELINE &&
bench_uprobe__setup_bpf_skel(bench) < 0)
^
tools/perf/bench/uprobe.c:155:14: note: Assuming 'i' is >= 'loops'
for (i = 0; i < loops; i++) {
^~~~~~~~~
tools/perf/bench/uprobe.c:155:2: note: Loop condition is false.
Execution continues on line 159
for (i = 0; i < loops; i++) {
^
tools/perf/bench/uprobe.c:164:2: note: Control jumps to 'case 1:' at line 169
switch (bench_format) {
^
tools/perf/bench/uprobe.c:171:3: note: Execution continues on line 179
break;
^
tools/perf/bench/uprobe.c:179:6: note: 'bench' is not equal to
BENCH_UPROBE__BASELINE
if (bench != BENCH_UPROBE__BASELINE)
^~~~~
tools/perf/bench/uprobe.c:179:2: note: Taking true branch
if (bench != BENCH_UPROBE__BASELINE)
^
tools/perf/bench/uprobe.c:180:3: note: Calling 'bench_uprobe__teardown_bpf_skel'
bench_uprobe__teardown_bpf_skel();
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tools/perf/bench/uprobe.c:97:6: note: 'skel' is non-null
if (skel) {
^~~~
tools/perf/bench/uprobe.c:97:2: note: Taking true branch
if (skel) {
^
tools/perf/bench/uprobe.c:98:3: note: Use of memory after it is freed
bench_uprobe_bpf__destroy(skel);
^ ~~~~
1 warning generated.
```
> Thanks,
> Namhyung
>
>
> > ---
> > tools/perf/bench/uprobe.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/tools/perf/bench/uprobe.c b/tools/perf/bench/uprobe.c
> > index 914c0817fe8a..5c71fdc419dd 100644
> > --- a/tools/perf/bench/uprobe.c
> > +++ b/tools/perf/bench/uprobe.c
> > @@ -89,6 +89,7 @@ static int bench_uprobe__setup_bpf_skel(enum bench_uprobe bench)
> > return err;
> > cleanup:
> > bench_uprobe_bpf__destroy(skel);
> > + skel = NULL;
> > return err;
> > }
> >
> > --
> > 2.42.0.609.gbb76f46606-goog
> >
