Messages in this thread | | | Date | Tue, 6 Mar 2012 18:49:25 -0600 | From | Peter Seebach <> | Subject | Re: [PATCH] perf: Incorrect use of snprintf results in SEGV |
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On Wed, 7 Mar 2012 11:42:49 +1100 Anton Blanchard <anton@samba.org> wrote:
> This patch fixes repsep_snprintf by clamping the value at size - 1 > which is the maximum snprintf can write before adding the NULL > terminator.
I would be concerned by this, simply because I at least sometimes use snprintf-like functions with the understanding that I can check for overflow by comparing the return value to the size.
... Of course, I think I also make this mistake you describe in other code, so I'm gonna go look for that.
But simply clamping the value might break code which is relying on the existing semantics. (And of course, any snprintf-related crash or misbehavior is likely to happen only when the planets are aligned just so...)
Possible alternative: Check for a provided size value which is unreasonably large, and if you get one, assume that it's probably intended to be negative and refuse to write anything. I don't know what unreasonably large is, but "large enough that it would have been negative had it been a signed type" might be a good starting point -- no one should be writing strings that long anyway*.
-s [*] I am totally ready for someone in twenty years to throw that quote in my face contemptuously as it shows that I was hopelessly short-sighted. -- Listen, get this. Nobody with a good compiler needs to be justified.
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