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Re: [PATCH] Adjust pointers to triplets in netgroup query data (BZ #16474)
- From: Andreas Schwab <schwab at linux-m68k dot org>
- To: OndÅej BÃlka <neleai at seznam dot cz>
- Cc: Siddhesh Poyarekar <siddhesh at redhat dot com>, libc-alpha at sourceware dot org
- Date: Fri, 24 Jan 2014 17:21:15 +0100
- Subject: Re: [PATCH] Adjust pointers to triplets in netgroup query data (BZ #16474)
- Authentication-results: sourceware.org; auth=none
- References: <20140121172451 dot GJ5544 at spoyarek dot pnq dot redhat dot com> <20140123123841 dot GA5631 at domone dot podge> <20140124085757 dot GA5544 at spoyarek dot pnq dot redhat dot com> <87d2jhtnl8 dot fsf at igel dot home> <20140124153727 dot GB14418 at domone dot podge>
OndÅej BÃlka <neleai@seznam.cz> writes:
> On Fri, Jan 24, 2014 at 04:18:43PM +0100, Andreas Schwab wrote:
>> Siddhesh Poyarekar <siddhesh@redhat.com> writes:
>>
>> > @@ -241,7 +241,17 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
>> > if (buflen - req->key_len - bufused < needed)
>> > {
>> > buflen += MAX (buflen, 2 * needed);
>> > - buffer = xrealloc (buffer, buflen);
>> > + char *newbuf = xrealloc (buffer, buflen);
>> > + /* Adjust the pointers in the new
>> > + buffer. */
>> > + nhost = (nhost ? newbuf + (nhost - buffer)
>>
>> This is undefined. If realloc was sucessful then buffer is no longer
>> valid. You need to compute nhost - buffer before doing the realloc.
>>
> As these are not referenced it leads to equivalent code.
That doesn't matter. It's undefined, period.
> Only problem with that code would be static analyzer flagging this as
> false positive.
And any future compiler that exploits the undefinedness. It's not a
false positive.
Andreas.
--
Andreas Schwab, schwab@linux-m68k.org
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