Re: C99 compliance for src/port/snprintf.c - Mailing list pgsql-hackers

From Andres Freund
Subject Re: C99 compliance for src/port/snprintf.c
Date
Msg-id 20180815215217.b3gnglunnxpxsl2d@alap3.anarazel.de
Whole thread Raw
In response to Re: C99 compliance for src/port/snprintf.c  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: C99 compliance for src/port/snprintf.c
List pgsql-hackers
On 2018-08-15 14:05:29 -0400, Tom Lane wrote:
> I wrote:
> > Meh --- the hazards of back-patching seem to me to be more hypothetical
> > than the benefits.  Still, I seem to be in the minority, so I withdraw
> > the proposal to back-patch.
> 
> Actually, after digging around a bit, I'm excited about this again.
> There are only a couple dozen places in our tree that pay any attention
> to the result of (v)snprintf, but with the exception of psnprintf,
> appendPQExpBufferVA, and one or two other places, *they're all assuming
> C99 semantics*, and will fail to detect buffer overflow with the pre-C99
> behavior.
> 
> Probably a lot of these are not live bugs because buffer overrun is
> not ever going to occur in practice.  But at least pg_upgrade and
> pg_regress are constructing command strings including externally
> supplied paths, so overrun doesn't seem impossible.  If it happened,
> they'd merrily proceed to execute a truncated command.
> 
> If we don't backpatch the snprintf change, we're morally obliged to
> back-patch some other fix for these places.  At least one of them,
> in plperl's pport.h, is not our code and so changing it seems like
> a bad idea.
> 
> Still want to argue for no backpatch?
> 
>             regards, tom lane
> 
> PS: I also found a couple of places that are just wrong regardless
> of semantics: they're checking overflow by "result > bufsize", not
> "result >= bufsize".  Will fix those in any case.

I'm a bit confused. Why did you just backpatch this ~two hours after
people objected to the idea?  Even if it were during my current work
hours, I don't even read mail that often if I'm hacking on something
complicated.

Greetings,

Andres Freund


pgsql-hackers by date:

Previous
From: Andres Freund
Date:
Subject: Re: C99 compliance for src/port/snprintf.c
Next
From: Tom Lane
Date:
Subject: Re: Stored procedures and out parameters