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

[Namhyung Kim]

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?
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@xxxxxxxxxx>
> ---
>  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
>