From: Martin Sebor <msebor@gmail.com>
To: Siddhesh Poyarekar <siddhesh@gotplt.org>,
GNU C Library <libc-alpha@sourceware.org>
Subject: Re: [PATCH] correct buffer end pointer in IO_wdefault_doallocate (BZ #26874)
Date: Mon, 1 Mar 2021 09:34:10 -0700 [thread overview]
Message-ID: <132620a1-02ad-bc47-3d39-7ce67840cbc4@gmail.com> (raw)
In-Reply-To: <4241c7d7-d028-3a38-1f36-94ba23af49ed@gotplt.org>
On 3/1/21 7:06 AM, Siddhesh Poyarekar wrote:
> On 2/4/21 3:17 PM, Siddhesh Poyarekar wrote:
>> On 1/2/21 4:04 AM, Martin Sebor via Libc-alpha wrote:
>>> An experimental build of GCC 11 with an enhanced -Warray-bounds
>>> reports a bug in IO_wdefault_doallocate where the function forms
>>> an invalid past-the-end pointer to an allocated wchar_t buffer
>>> by failingf to consider the scaling by sizeof (wchar_t).
>>>
>>> The fix path below corrects this problem. It keeps the buffer
>>> size the same as opposed to increasing it according to what other
>>> code like it does.
>>>
>>> Since the bug looks like it might be exploitable I tried to create
>>> a test case to trigger a call to _IO_wdefault_doallocate but couldn't.
>>> No test in the test suite seems to either, so I post this patch without
>>> one.
>>
>> I spent some time following those vtable setups and I don't think
>> _IO_wdefault_doallocate gets called at all. The only instances it is
>> set as the doallocate callback are in strops, wmemstream and in
>> vswprintf. In all those cases, the backing buffer is either user
>> supplied or is sized without using doallocate (as in the case of
>> strops overflow).
>>
>> The only time libio needs to allocate buffers in the wide context is
>> in wfileops when it's actually using the underlying buffer. In that
>> case however, the doallocate callback is different.
>>
>> Nevertheless, this is a good cleanup, so LGTM.
>
> Martin, I've pushed this patch for you.
Thanks! (And sorry for not getting to it myself. I'm behind on
a number of fronts.)
Martin
>
> Siddhesh
prev parent reply other threads:[~2021-03-01 16:34 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-01 22:34 Martin Sebor
2021-02-04 9:47 ` Siddhesh Poyarekar
2021-03-01 14:06 ` Siddhesh Poyarekar
2021-03-01 16:34 ` Martin Sebor [this message]
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