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Date: Fri, 10 Mar 2023 19:28:18 +0300 (MSK)
From: Alexander Monakov <amonakov@...ras.ru>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] getopt: fix null pointer arithmetic ub
Hi,
On Fri, 10 Mar 2023, Alexey Izbyshev wrote:
> When an option that requires an argument is the last character of
> argv[argc-1], getopt computes argv[argc] + optpos. While optpos
> is always zero in this case, adding it to null pointer is still
> undefined.
> ---
> src/misc/getopt.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/src/misc/getopt.c b/src/misc/getopt.c
> index c3f66995..af12973a 100644
> --- a/src/misc/getopt.c
> +++ b/src/misc/getopt.c
> @@ -87,7 +87,8 @@ int getopt(int argc, char * const argv[], const char *optstring)
> if (optstring[i] == ':') {
> optarg = 0;
> if (optstring[i+1] != ':' || optpos) {
> - optarg = argv[optind++] + optpos;
> + optarg = argv[optind++];
> + if (optarg) optarg += optpos;
Can this be written as 'if (optpos) optarg += optpos;' instead? That will be
folded back into plain addition by the compiler.
(also (unlike the quoted variant) would allow undefined behavior
instrumentation to catch attempted NULL pointer arithmetic)
Alexander
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