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Message-ID: <18659a22996ae335c466e9f92d0dd84b@ispras.ru>
Date: Fri, 10 Mar 2023 19:59:09 +0300
From: Alexey Izbyshev <izbyshev@...ras.ru>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] getopt: fix null pointer arithmetic ub
On 2023-03-10 19:28, Alexander Monakov wrote:
> 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.
>
Yes, "if (optpos) ..." is actually what I initially wrote before
changing it to the submitted variant. I'm fine with changing it back;
thanks for the codegen check.
> (also (unlike the quoted variant) would allow undefined behavior
> instrumentation to catch attempted NULL pointer arithmetic)
>
Yes, a good point too.
Alexey
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