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From Jacob Champion <champio...@gmail.com>
Subject Re: httpd 2.4.25, mpm_event, ssl: segfaults
Date Thu, 02 Feb 2017 22:19:04 GMT
On 02/02/2017 02:04 AM, Yann Ylavic wrote:
> Hi Niklas,
>
> On Wed, Feb 1, 2017 at 7:02 PM, Niklas Edmundsson <nikke@acc.umu.se> wrote:
>>
>> We've started to see spurious segfaults with httpd 2.4.25, mpm_event, ssl on
>> Ubuntu 14.04LTS. Not frequent, but none the less happening.
>>
>> #4  ssl_io_filter_output (f=0x7f507013cfe0, bb=0x7f4f840be168) at
>> ssl_engine_io.c:1746
>>         data = 0x7f5075518000 <error: Cannot access memory at address
>> 0x7f5075518000>
>>         len = 4194304
>>         bucket = 0x7f4f840b1ba8
>>         status = <optimized out>
>>         filter_ctx = 0x7f507013cf88
>>         inctx = <optimized out>
>>         outctx = 0x7f507013d008
>>         rblock = APR_NONBLOCK_READ

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.

Niklas, what version of APR are you using? Are you serving large (> 4 
MiB) static files? I have not been able to reproduce so far (Ubuntu 
16.04, httpd 2.4.25 + mod_ssl + mpm_event).

--Jacob

[1] 
https://stackoverflow.com/questions/654393/examining-mmaped-addresses-using-gdb

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