Re: [PATCH 01/11] mingw: avoid accessing uninitialized memory in `is_executable()`

From: René Scharfe <l.s.r@web.de>
Date: Jun 16, 2022, 19:53 UTC
Message-ID: <98ff788a-d621-cf3f-aed5-66ae763b381f@web.de>
In-Reply-To: <679ea7421f73ce41515aca549982233f88bcefef.1655336146.git.gitgitgadget@gmail.com>

Am 16.06.22 um 01:35 schrieb Johannes Schindelin via GitGitGadget:

Show 6 quoted lines

> From: Johannes Schindelin <johannes.schindelin@gmx.de>
>
> On Windows, we open files we suspect might be scripts, read the first
> two bytes, and see whether they indicate a hash-bang line. We do not
> initialize the byte _after_ those two bytes, therefore `strcmp()` is
> inappropriate here.

Hmm, but buf _is_ initialized fully?  Line 149:

        char buf[3] = { 0 };

C99 §6.7.8 21: "If there are [...] fewer characters in a string literal used to initialize an array of known size than there are elements in the array, the remainder of the aggregate shall be initialized implicitly the same as objects that have static storage duration."

Show 21 quoted lines

>
> Reported by Coverity.
>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>  run-command.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/run-command.c b/run-command.c
> index 14f17830f51..2ba38850b4d 100644
> --- a/run-command.c
> +++ b/run-command.c
> @@ -154,7 +154,7 @@ int is_executable(const char *name)
>  		n = read(fd, buf, 2);
>  		if (n == 2)
>  			/* look for a she-bang */
> -			if (!strcmp(buf, "#!"))
> +			if (!memcmp(buf, "#!", 2))
>  				st.st_mode |= S_IXUSR;
>  		close(fd);
>  	}