Re: [PATCH 2/2] perf tools: Fix fault in tracepoint_error if NULL is passed to parse_event

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Mon, Feb 01, 2016 at 10:53:29AM +0200, Adrian Hunter escreveu:
> On 01/02/16 05:21, Wang Nan wrote:
> > Following segfault can happen with a non-root user:
> > 
> >  $ ./perf record -I -e intel_pt/tsc=1,noretcomp=1/u /bin/ls
> >  WARNING: Kernel address maps (/proc/{kallsyms,modules}) are restricted,
> >  check /proc/sys/kernel/kptr_restrict.
> > 
> >  Samples in kernel functions may not be resolved if a suitable vmlinux
> >  file is not found in the buildid cache or in the vmlinux path.
> > 
> >  Samples in kernel modules won't be resolved at all.
> > 
> >  If some relocation was applied (e.g. kexec) symbols may be misresolved
> >  even with a suitable vmlinux or kallsyms file.
> > 
> >  Segmentation fault (core dumped)
> > 
> > The error is in tracepoint_error: it assumes 'e' is valid.
> > 
> > However, there are many situation a parse_event can be called without
> > parse_events_error. See result of
> > 'grep 'parse_events(.*NULL)' ./tools/perf/ -r'.
> > 
> > This patch makes tracepoint_error() directly return when !e.
> 
> I sent the same fix here:
> 
> 	http://marc.info/?l=linux-kernel&m=145381056111871

Yeah, I couldn't reproduce it, but we narrowed that down to: machine
with Intel PT, without perf_event_attr.context_switch, non-root user,
i.e. user can't access the debugfs events info, rebooted my new machine
with:

[root@jouet ~]# uname -r
4.2.3-300.fc23.x86_64

And, as root, all works because it can read the debugfs events info, to
get the "sched:sched_switch" infoa:

[root@jouet ~]# perf record -I -e intel_pt/tsc=1,noretcomp=1/u /bin/ls
0  a  anaconda-ks.cfg  bin  GBPCEFwr64.tar-from-deb  perf.data
perf.data.old  perf-f23-bringup.todo
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.214 MB perf.data ]
[root@jouet ~]# perf evlist
intel_pt/tsc=1,noretcomp=1/u
sched:sched_switch
dummy:u
# Tip: use 'perf evlist --trace-fields' to show fields for tracepoint
# events
[root@jouet ~]#

But not as a non priledged user:

(gdb) run record -I -e intel_pt/tsc=1,noretcomp=1/u /bin/ls
Starting program:  record -I -e intel_pt/tsc=1,noretcomp=1/u /bin/ls
No executable file specified.
Use the "file" or "exec-file" command.
(gdb) file perf
Reading symbols from perf...done.
(gdb) run record -I -e intel_pt/tsc=1,noretcomp=1/u /bin/ls
Starting program: /home/acme/bin/perf record -I -e intel_pt/tsc=1,noretcomp=1/u /bin/ls
Missing separate debuginfos, use: dnf debuginfo-install glibc-2.22-7.fc23.x86_64
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Program received signal SIGSEGV, Segmentation fault.
0x00000000004b9ea5 in tracepoint_error (e=0x0, err=13, sys=0x19b1370 "sched", name=0x19a5d00 "sched_switch") at util/parse-events.c:410
410			e->str = strdup("can't access trace events");
Missing separate debuginfos, use: dnf debuginfo-install audit-libs-2.4.5-1.fc23.x86_64 bzip2-libs-1.0.6-18.fc23.x86_64 elfutils-libelf-0.165-2.fc23.x86_64 elfutils-libs-0.165-2.fc23.x86_64 libunwind-1.1-10.fc23.x86_64 nss-softokn-freebl-3.21.0-1.1.fc23.x86_64 numactl-libs-2.0.10-3.fc23.x86_64 perl-libs-5.22.1-350.fc23.x86_64 python-libs-2.7.10-8.fc23.x86_64 slang-2.3.0-4.fc23.x86_64 xz-libs-5.2.1-3.fc23.x86_64 zlib-1.2.8-9.fc23.x86_64
(gdb) bt
#0  0x00000000004b9ea5 in tracepoint_error (e=0x0, err=13, sys=0x19b1370 "sched", name=0x19a5d00 "sched_switch") at util/parse-events.c:410
#1  0x00000000004b9fc5 in add_tracepoint (list=0x19a5d20, idx=0x7fffffffb8c0, sys_name=0x19b1370 "sched", evt_name=0x19a5d00 "sched_switch", err=0x0, head_config=0x0)
    at util/parse-events.c:433
#2  0x00000000004ba334 in add_tracepoint_event (list=0x19a5d20, idx=0x7fffffffb8c0, sys_name=0x19b1370 "sched", evt_name=0x19a5d00 "sched_switch", err=0x0, head_config=0x0)
    at util/parse-events.c:498
#3  0x00000000004bb699 in parse_events_add_tracepoint (list=0x19a5d20, idx=0x7fffffffb8c0, sys=0x19b1370 "sched", event=0x19a5d00 "sched_switch", err=0x0, head_config=0x0)
    at util/parse-events.c:936
#4  0x00000000004f6eda in parse_events_parse (_data=0x7fffffffb8b0, scanner=0x19a49d0) at util/parse-events.y:391
#5  0x00000000004bc8e5 in parse_events__scanner (str=0x663ff2 "sched:sched_switch", data=0x7fffffffb8b0, start_token=258) at util/parse-events.c:1361
#6  0x00000000004bca57 in parse_events (evlist=0x19a5220, str=0x663ff2 "sched:sched_switch", err=0x0) at util/parse-events.c:1401
#7  0x0000000000518d5f in perf_evlist__can_select_event (evlist=0x19a3b90, str=0x663ff2 "sched:sched_switch") at util/record.c:253
#8  0x0000000000553c42 in intel_pt_track_switches (evlist=0x19a3b90) at arch/x86/util/intel-pt.c:364
#9  0x00000000005549d1 in intel_pt_recording_options (itr=0x19a2c40, evlist=0x19a3b90, opts=0x8edf68 <record+232>) at arch/x86/util/intel-pt.c:664
#10 0x000000000051e076 in auxtrace_record__options (itr=0x19a2c40, evlist=0x19a3b90, opts=0x8edf68 <record+232>) at util/auxtrace.c:539
#11 0x0000000000433368 in cmd_record (argc=1, argv=0x7fffffffde60, prefix=0x0) at builtin-record.c:1264
#12 0x000000000049bec2 in run_builtin (p=0x8fa2a8 <commands+168>, argc=5, argv=0x7fffffffde60) at perf.c:390
#13 0x000000000049c12a in handle_internal_command (argc=5, argv=0x7fffffffde60) at perf.c:451
#14 0x000000000049c278 in run_argv (argcp=0x7fffffffdcbc, argv=0x7fffffffdcb0) at perf.c:495
#15 0x000000000049c60a in main (argc=5, argv=0x7fffffffde60) at perf.c:618
(gdb) 

I am applying Adrian's original patch, adding the above explanations and
parts of Wang's, the one about grep showing that that parameter can ben NULL while
the function doesn't check it.

- Arnaldo
 
> > Signed-off-by: Wang Nan <wangnan0@huawei.com>
> > Cc: Adrian Hunter <adrian.hunter@intel.com>
> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> > Cc: Tong Zhang <ztong@vt.edu>

> > Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> > ---
> >  tools/perf/util/parse-events.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> > index 4f7b0ef..813d9b2 100644
> > --- a/tools/perf/util/parse-events.c
> > +++ b/tools/perf/util/parse-events.c
> > @@ -399,6 +399,9 @@ static void tracepoint_error(struct parse_events_error *e, int err,
> >  {
> >  	char help[BUFSIZ];
> >  
> > +	if (!e)
> > +		return;
> > +
> >  	/*
> >  	 * We get error directly from syscall errno ( > 0),
> >  	 * or from encoded pointer's error ( < 0).
> >