linux-kernel - Re: [BUGFIX PATCH v2.1] tracing: probeevent: Fix to support minus offset from symbol

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Message-ID: <20180223001542.GA25299@sejong>
Date:   Fri, 23 Feb 2018 09:15:42 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Masami Hiramatsu <mhiramat@...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: [BUGFIX PATCH v2.1] tracing: probeevent: Fix to support minus
 offset from symbol

Hi Masami,

On Thu, Feb 22, 2018 at 04:45:01PM +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.
> 
> Fixes: 2fba0c8867af ("tracing/kprobes: Fix probe offset to be unsigned")
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  Changes in v2.1:
>   - Fix to ensure the offset value is less than LONG_MAX.
>   - Fail if the offset is minus when traceprobe_split_symbol_offset()
>     is used for the probe address.
>   - Add Fixes tag.
> ---
>  kernel/trace/trace_kprobe.c |    4 ++--
>  kernel/trace/trace_probe.c  |   15 ++++++++++-----
>  kernel/trace/trace_probe.h  |    2 +-
>  3 files changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 5ce9b8cf7be3..b5b1d8aa47d6 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) {
>  			pr_info("Failed to parse either an address or a symbol.\n");
>  			return ret;
>  		}
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index d59357308677..ec3856147fdd 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -320,21 +320,26 @@ 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)
>  {
> +	unsigned long ul;
>  	char *tmp;
>  	int ret;
>  
>  	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 = kstrtoul(tmp + 1, 0, &ul);

Why not just using kstrtol() which handles the sign correctly?

Thanks,
Namhyung


>  		if (ret)
>  			return ret;
> -
> +		if (ul > LONG_MAX)
> +			return -E2BIG;
> +		if (*tmp == '-')
> +			*offset = -ul;
> +		else
> +			*offset = ul;
>  		*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
>