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From Yann Ylavic <ylavic....@gmail.com>
Subject Re: httpd 2.4.25, mpm_event, ssl: segfaults
Date Thu, 02 Feb 2017 23:05:52 GMT
On Thu, Feb 2, 2017 at 11:36 PM, Jacob Champion <champion.p@gmail.com> wrote:
> On 02/02/2017 02:32 PM, Yann Ylavic wrote:
>>
>> On Thu, Feb 2, 2017 at 11:19 PM, Jacob Champion <champion.p@gmail.com>
>> wrote:
>>>
>>> Idle thoughts: "Cannot access memory" in this case could be a red
>>> herring,
>>> if Niklas' gdb can't peer into mmap'd memory spaces [1]. It seems
>>> reasonable
>>> that the data in question could be mmap'd, given the nice round address
>>> and
>>> 4 MiB length (equal to APR_MMAP_LIMIT).
>>>
>>> That doesn't mean we're looking in the wrong place, though, since SIGBUS
>>> can
>>> also be generated by an out-of-bounds access to an mmap'd region.
>>
>>
>> Right, looks like the memory has been unmapped though (SIGBUS) before
>> being (re)used.
>
> Oh, I thought an access after an unmap would SIGSEGV instead of SIGBUS. I
> haven't ever tested that out; I should try it...

Hmm, Linux raises SIGBUS if an mmap is used after the underlying file
has been truncated (see [1]).

Couldn't htcacheclean or alike do something like this?
"EnableMMAP off" could definitely help here.

[1] http://man7.org/linux/man-pages/man2/mmap.2.html

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