linux-kernel - Issue with 'lib/vsprintf.c: don't try to fix pointer wrap-around'

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Message-ID: <20150116162357.GA10859@phnom.home.cmpxchg.org>
Date:	Fri, 16 Jan 2015 11:23:57 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Issue with 'lib/vsprintf.c: don't try to fix pointer wrap-around'

Hi Rasmus,

I have trouble booting my test machine with this patch in -mm:

commit bb2e066c6943e62e9650bb129f416dacf138f8b1
Author: Rasmus Villemoes <linux@...musvillemoes.dk>
Date:   Wed Jan 14 01:00:44 2015 +0000

    lib/vsprintf.c: don't try to fix pointer wrap-around
    
    Actual kernel buffers can't wrap into the user address space.  If someone
    manages to pass a buf/size combination that wraps, it is most likely due
    to a bug in the caller.  Instead of trying to fix it by using a smaller
    part of the buffer, bail out.
    
    Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
    Cc: Jiri Kosina <jkosina@...e.cz>
    Cc: Randy Dunlap <rdunlap@...radead.org>
    Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>

After I get "Loading bzImage-new... ok" from the bootloader, the
serial console remains quiet.

A WARN_ON_ONCE() inside vsnprintf() looks like it would deadlock
instantly when triggering this overflow from printk(), no?
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