linux-kernel - Re: [PATCH] perf probe: Added protection to avoid endless loop

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Date:   Wed, 3 Feb 2021 22:25:02 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Jianlin Lv <Jianlin.Lv@....com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org, srikar@...ux.vnet.ibm.com,
        adrian.hunter@...el.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf probe: Added protection to avoid endless loop

On Wed,  3 Feb 2021 10:25:07 +0800
Jianlin Lv <Jianlin.Lv@....com> wrote:

> if dwarf_offdie() return NULL, the continue statement forces the next
> iteration of the loop without update variable off. It will cause an
> endless loop in the process of traversing the compilation unit.
> So added exception protection for loop CUs.

Good catch!

> 
> Signed-off-by: Jianlin Lv <Jianlin.Lv@....com>
> ---
>  tools/perf/util/probe-finder.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> index 76dd349aa48d..887bffb1cc58 100644
> --- a/tools/perf/util/probe-finder.c
> +++ b/tools/perf/util/probe-finder.c
> @@ -1156,7 +1156,7 @@ static int debuginfo__find_probe_location(struct debuginfo *dbg,
>  	Dwarf_Die *diep;
>  	int ret = 0;
>  
> -	off = 0;
> +	noff = 0;
>  	pf->lcache = intlist__new(NULL);
>  	if (!pf->lcache)
>  		return -ENOMEM;
> @@ -1184,7 +1184,7 @@ static int debuginfo__find_probe_location(struct debuginfo *dbg,
>  	}
>  
>  	/* Loop on CUs (Compilation Unit) */
> -	while (!dwarf_nextcu(dbg->dbg, off, &noff, &cuhl, NULL, NULL, NULL)) {
> +	while (!dwarf_nextcu(dbg->dbg, off = noff, &noff, &cuhl, NULL, NULL, NULL)) {

I don't like to update variable in function argument, 

I would rather like below code;

>  		/* Get the DIE(Debugging Information Entry) of this CU */
>  		diep = dwarf_offdie(dbg->dbg, off + cuhl, &pf->cu_die);
  		if (!diep) {
+			off = noff;
			continue;
		}

Or, "goto next;" and

> @@ -1208,7 +1208,6 @@ static int debuginfo__find_probe_location(struct debuginfo *dbg,
>  			if (ret < 0)
>  				break;
>  		}

next:

> -		off = noff;
>  	}
>  
>  found:
> @@ -1919,7 +1918,7 @@ int debuginfo__find_line_range(struct debuginfo *dbg, struct line_range *lr)
>  {
>  	struct line_finder lf = {.lr = lr, .found = 0};
>  	int ret = 0;
> -	Dwarf_Off off = 0, noff;
> +	Dwarf_Off off = 0, noff = 0;
>  	size_t cuhl;
>  	Dwarf_Die *diep;
>  	const char *comp_dir;
> @@ -1943,6 +1942,7 @@ int debuginfo__find_line_range(struct debuginfo *dbg, struct line_range *lr)
>  
>  	/* Loop on CUs (Compilation Unit) */
>  	while (!lf.found && ret >= 0) {
> +		off = noff;

Here too.
Can you update it?

Thank you,

>  		if (dwarf_nextcu(dbg->dbg, off, &noff, &cuhl,
>  				 NULL, NULL, NULL) != 0)
>  			break;
> @@ -1967,7 +1967,6 @@ int debuginfo__find_line_range(struct debuginfo *dbg, struct line_range *lr)
>  				ret = find_line_range_by_line(NULL, &lf);
>  			}
>  		}
> -		off = noff;
>  	}
>  
>  found:
> -- 
> 2.25.1
> 


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