kern/163076: It is not possible to read in chunks from linprocfs
jh at FreeBSD.org
Sun Dec 11 10:30:05 UTC 2011
The following reply was made to PR kern/163076; it has been noted by GNATS.
From: Jaakko Heinonen <jh at FreeBSD.org>
To: Poul-Henning Kamp <phk at phk.freebsd.dk>
Cc: Petr Salinger <Petr.Salinger at seznam.cz>, bug-followup at FreeBSD.org,
des at FreeBSD.org, mdf at FreeBSD.org
Subject: Re: kern/163076: It is not possible to read in chunks from linprocfs
Date: Sun, 11 Dec 2011 12:26:08 +0200
On 2011-12-10, Poul-Henning Kamp wrote:
> I agree with Dag-Erling that it is at least mistake to not have
> separate sbuf(9) and sbuf(3) pages, possibly also a mistake that
> they share the implementation.
One problem is the different malloc() semantics. The kernel version uses
M_WAITOK allocations while user space malloc(3) can fail.
> Obviously sbuf_finish() should return the error status, and its
> return value SHALL be checked by applications, before the contents
> of the sbuf can be used.
Only 21 of 133 calls I grepped through the FreeBSD source tree did check
the return value. In practice SBUF_AUTOEXTEND buffers can't fail when
the kernel version is used (due to M_WAITOK malloc).
> The argument relating to this bug is about what sbuf_len() and
> sbuf_data() should return for an error'ed sbuf.
> Given that the mandatory error-check of the sbuf_finish() call
> should prevent these two functions from being called in the first
> place, I'm tempted to say that their return values should be
> documented as undefined, and implemented to cause the maxium amount
> of havoc (ie: -1 and NULL).
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