[Xymon] Possible bug in xymon svcstatus causing segfault (buffer overrun?)

[Jeremy Laidman]

Mario

Attached is a diff to the file that I used. It's against version 4.3.30.

Cheers
Jeremy


On Sat, 1 Jun 2024 at 06:29, Mario <rower.master at gmail.com> wrote:

>
> Hello Jeremy/JC,
>
> I´m facing the same issue with switches interfaces graphs not loading in
> trends or causing internal server error.
> Do you have a patch to fix this?
> Or maybe I need to downgrade xymon 4.3.30 version?
>
>
> Thanks & regards,
> Mario
>
>
>
> On Wed, Sep 13, 2023 at 4:59 AM Jeremy Laidman <jeremy at laidman.org> wrote:
>
>> Ugh, just saw your reply in my spam folder!
>>
>> On Fri, 1 Sept 2023 at 23:40, J.C. Cleaver <cleaver at terabithia.org>
>> wrote:
>>
>>>
>>> On Tue, August 29, 2023 23:40, Jeremy Laidman wrote:
>>>
>>> >
>>> > Elsewhere in other code, the SBUF_REALLOC macro is used to add extra
>>> > bufferspace by calculating a new buffer size of [existing buffer size
>>> plus
>>> > 4k plus the length of the string being added]. So if the string to be
>>> > added
>>> > had 20 bytes, SBUF_REALLOC would be used to add 4k+20 bytes to the
>>> buffer
>>> > size. Notably, the size of the string is included in the calculation.
>>> For
>>> > example this bit of code elsewhere in the same file does a similar
>>> buffer
>>> > extension:
>>> >
>>> >                         if ((strlen(rrdlink) + strlen(partlink) + 1) >=
>>> > rrdlink_buflen) {
>>> >                                 SBUF_REALLOC(rrdlink, rrdlink_buflen +
>>> > strlen(partlink) + 4096);
>>> >                         }
>>> >                         strncat(rrdlink, partlink, (rrdlink_buflen -
>>> > strlen(rrdlink)));
>>> >
>>> > Note the extra "+ strlen(<stringvar>)" bit in the extra memory being
>>> > allocated that isn't there in the first block of code above. So my
>>> > thinking
>>> > is that the SBUF_REALLOC() needs to take the string's size into
>>> account,
>>> > like so:
>>> >
>>> >                                 SBUF_REALLOC(allrrdlinks,
>>> > allrrdlinks_buflen+strlen(onelink)+4096);
>>> >
>>> > Is anyone with C skills able to confirm that this does indeed look
>>> like a
>>> > bug, and also that my proposed change is a suitable fix? After applying
>>> > this change and recompiling, we haven't yet seen a seg fault from this
>>> bit
>>> > of code, so I'm hoping it's all fixed, and without negative side
>>> effects.
>>> >
>>> > Cheers
>>> > Jeremy
>>>
>>> Based on my looking over it, I would confirm that this seems to be a bug.
>>> Specifically, it looks like we missed this part of the fix in
>>> https://sourceforge.net/p/xymon/code/8069/?page=7#diff-1 while trying to
>>> get ahead of possible buffer overflows for various CVE's
>>> (https://nvd.nist.gov/vuln/detail/CVE-2019-13486, I suppose). I can't
>>> see
>>> a reason not to add the length in here without a guard somewhere else for
>>> the length.
>>>
>>> Furthermore, other uses of this macro pretty much all include the length
>>> of the incoming string or limit the concat to a specific size, which
>>> obviously isn't ideal for URLs here.
>>>
>>> If you have a reproducer and your patch fixes it, I suspect that will be
>>> sufficient and we can add it in. Can you send a coredump from a crash off
>>> list by any chance (using the debuginfo RPMs) just to double-check?
>>>
>>
>> Sorry, can you define "reproducer"? Is that a coding term I haven't yet
>> come across?
>>
>> I have core dumps, but I'll see about using the debuginfo RPMs (assuming
>> they're on Terabithia) and get a core dump from an install of that.
>>
>> Thanks
>> _______________________________________________
>> Xymon mailing list
>> Xymon at xymon.com
>> http://lists.xymon.com/mailman/listinfo/xymon
>>
>
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