linux-kernel - Re: [PATCH v4 01/19] [BUGFIX] tracing: probeevent: Fix to support minus offset from symbol

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Message-Id: <20180302153229.dbc4dc9be90a0132b7010010@kernel.org>
Date:   Fri, 2 Mar 2018 15:32:29 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-trace-users@...r.kernel.org, linux-kselftest@...r.kernel.org,
        shuah@...nel.org, kernel-team@....com
Subject: Re: [PATCH v4 01/19] [BUGFIX] tracing: probeevent: Fix to support
 minus offset from symbol

On Fri, 2 Mar 2018 13:49:51 +0900
Namhyung Kim <namhyung@...nel.org> wrote:

> Hi Masami,
> 
> On Wed, Feb 28, 2018 at 12:19:53PM +0900, Masami Hiramatsu wrote:
> > In Documentation/trace/kprobetrace.txt, it says
> > 
> >  @SYM[+|-offs] : Fetch memory at SYM +|- offs (SYM should be a data symbol)
> > 
> > However, the parser doesn't parse minus offset correctly, since
> > commit 2fba0c8867af ("tracing/kprobes: Fix probe offset to be
> > unsigned") drops minus ("-") offset support for kprobe probe
> > address usage.
> > 
> > This fixes the traceprobe_split_symbol_offset() to parse minus
> > offset again with checking the offset range, and add a minus
> > offset check in kprobe probe address usage.
> 
> It now parses a minus offset but doesn't allow it, right?

No, split_symbol_offset() is used for 2 cases
 - kprobe-event probe point
 - kporbe-event symbol-based argument

Former one doesn't accept a minus offset, but latter accepts it.

(Frankly to say, I guess no one care about supporting minus offset :P)

Thanks,

> Then I still think it's better to fix the documentation.
> 
> 
> > 
> > Fixes: 2fba0c8867af ("tracing/kprobes: Fix probe offset to be unsigned")
> > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> > ---
> >  Changes in v3:
> >   - Use kstrtol instead of kstrtoul. (Thanks Namhyung!)
> >  Changes in v4:
> >   - Fix to decode sign. (Thanks Namhyung!)
> >   - Fix to check UINT_MAX for kprobe offset.
> > ---
> >  kernel/trace/trace_kprobe.c |    4 ++--
> >  kernel/trace/trace_probe.c  |    8 +++-----
> >  kernel/trace/trace_probe.h  |    2 +-
> >  3 files changed, 6 insertions(+), 8 deletions(-)
> > 
> > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> > index 5ce9b8cf7be3..1cd3fb4d70f8 100644
> > --- a/kernel/trace/trace_kprobe.c
> > +++ b/kernel/trace/trace_kprobe.c
> > @@ -667,7 +667,7 @@ static int create_trace_kprobe(int argc, char **argv)
> >  	char *symbol = NULL, *event = NULL, *group = NULL;
> >  	int maxactive = 0;
> >  	char *arg;
> > -	unsigned long offset = 0;
> > +	long offset = 0;
> >  	void *addr = NULL;
> >  	char buf[MAX_EVENT_NAME_LEN];
> >  
> > @@ -755,7 +755,7 @@ static int create_trace_kprobe(int argc, char **argv)
> >  		symbol = argv[1];
> >  		/* TODO: support .init module functions */
> >  		ret = traceprobe_split_symbol_offset(symbol, &offset);
> > -		if (ret) {
> > +		if (ret || offset < 0 || offset > UINT_MAX) {
> >  			pr_info("Failed to parse either an address or a symbol.\n");
> >  			return ret;
> 
> Wouldn't it be confusing if it returns 0 for an invalid input?
> 
> Thanks,
> Namhyung
> 
> 
> >  		}
> > diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> > index d59357308677..daf54bda4dc8 100644
> > --- a/kernel/trace/trace_probe.c
> > +++ b/kernel/trace/trace_probe.c
> > @@ -320,7 +320,7 @@ static fetch_func_t get_fetch_size_function(const struct fetch_type *type,
> >  }
> >  
> >  /* Split symbol and offset. */
> > -int traceprobe_split_symbol_offset(char *symbol, unsigned long *offset)
> > +int traceprobe_split_symbol_offset(char *symbol, long *offset)
> >  {
> >  	char *tmp;
> >  	int ret;
> > @@ -328,13 +328,11 @@ int traceprobe_split_symbol_offset(char *symbol, unsigned long *offset)
> >  	if (!offset)
> >  		return -EINVAL;
> >  
> > -	tmp = strchr(symbol, '+');
> > +	tmp = strpbrk(symbol, "+-");
> >  	if (tmp) {
> > -		/* skip sign because kstrtoul doesn't accept '+' */
> > -		ret = kstrtoul(tmp + 1, 0, offset);
> > +		ret = kstrtol(tmp, 0, offset);
> >  		if (ret)
> >  			return ret;
> > -
> >  		*tmp = '\0';
> >  	} else
> >  		*offset = 0;
> > diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> > index 0745f895f780..75daff22ccea 100644
> > --- a/kernel/trace/trace_probe.h
> > +++ b/kernel/trace/trace_probe.h
> > @@ -365,7 +365,7 @@ extern int traceprobe_conflict_field_name(const char *name,
> >  extern void traceprobe_update_arg(struct probe_arg *arg);
> >  extern void traceprobe_free_probe_arg(struct probe_arg *arg);
> >  
> > -extern int traceprobe_split_symbol_offset(char *symbol, unsigned long *offset);
> > +extern int traceprobe_split_symbol_offset(char *symbol, long *offset);
> >  
> >  /* Sum up total data length for dynamic arraies (strings) */
> >  static nokprobe_inline int
> > 


-- 
Masami Hiramatsu <mhiramat@...nel.org>