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Re: openssh do_log function has larger than needed buffer?

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Mike Small <smallm@sdf.org> writes:

> I was looking at a function in OpenSSH that prepares a string for
> logging and calls syslog with a format string limiting the length of
> what is written. I'm puzzled by the difference between the size of the
> char array used to compose the string (1024 bytes) and the limit on the
> number of its characters that could be output by syslog (format
> specifier "%.500s").

It looks like maybe a hang-over from when the code had hand-coded
sizes.  Or maybe there was a reason to further limit the logging via
routes?  Hard to say.

> The only potential explanation I could think of was that it might have
> something to do with multibyte strings, that maybe a string could be
> devised such that the buffer would overrun from use of characters
> encoded by more than one byte. But looking at the function calls before
> the syslog call I'm thinking the string should be guaranteed to be nul
> terminated, which I think prevents overrun even if there are multibyte
> characters included.

Yup.  It can't be that.  I think it's just an accident.

But if you want a belt-and-braces approach, put a null at the end of the
array just before using %s and you can be sure the logging function
won't read beyond that.

<snip>
-- 
Ben.

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openssh do_log function has larger than needed buffer? Mike Small <smallm@sdf.org> - 2017-03-15 19:49 +0000
  Re: openssh do_log function has larger than needed buffer? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-03-16 14:25 +0000

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