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SubjectRe: [PATCH] tracing/eprobe: Replace kzalloc with kmalloc
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Le 07/01/2023 à 04:45, Quanfa Fu a écrit :
> Since this memory will be filled soon below, I feel that there is
> no need for a memory of all zeros here. 'snprintf' does not return
> negative num according to ISO C99, so I feel that no judgment is
> needed here.
>
> No functional change intended.
>
> Signed-off-by: Quanfa Fu <quanfafu@gmail.com>
> ---
> kernel/trace/trace_eprobe.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
> index 352b65e2b910..cd1d271a74e7 100644
> --- a/kernel/trace/trace_eprobe.c
> +++ b/kernel/trace/trace_eprobe.c
> @@ -917,15 +917,13 @@ static int trace_eprobe_parse_filter(struct trace_eprobe *ep, int argc, const ch
> for (i = 0; i < argc; i++)
> len += strlen(argv[i]) + 1;
>
> - ep->filter_str = kzalloc(len, GFP_KERNEL);
> + ep->filter_str = kmalloc(len, GFP_KERNEL);
> if (!ep->filter_str)
> return -ENOMEM;
>
> p = ep->filter_str;
> for (i = 0; i < argc; i++) {
> ret = snprintf(p, len, "%s ", argv[i]);
> - if (ret < 0)
> - goto error;
> if (ret > len) {

Hi,

as per [1]:
* The return value is the number of characters which would be
* generated for the given input, excluding the trailing null,
* as per ISO C99. If the return is greater than *or equal* to
* @size, the resulting string is truncated.

So, should this test be:
if (ret >= len)
~~~~


Also, isn't the p[-1] = '\0' after the loop eating the last character?
argc = 1;
argv[0] = "a";

Before the loop:
===============
len = 1 + 1 = 2;
ep->filter_str = 0x00 0x00
^
|___ p

After the loop:
===============
ep->filter_str = 0x61 0x00
^
|___ p
len = 1;

After p[-1]:
============
ep->filter_str = 0x00 0x00
~~ ^
|___ p

Did I miss something obvious?
I don't know the intent here, or if it is an issue at all, but it looks odd.

CJ


[1]: https://elixir.bootlin.com/linux/v6.2-rc1/source/lib/vsprintf.c#L2925
> ret = -E2BIG;
> goto error;

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