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Subject: Re: 2.4.20 copy_from/to_user
From: Gianni Tedesco <gianni@ecsc.co.uk>
To: Margit Schubert-While <margitsw@t-online.de>
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <4.3.2.7.2.20021217112614.00b55eb0@pop.t-online.de>
References: <4.3.2.7.2.20021217112614.00b55eb0@pop.t-online.de>
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On Tue, 2002-12-17 at 10:42, Margit Schubert-While wrote:
> Maybe talking through the top of my hat , however -
> copy_from_user and copy_to_user are used all over the place and the
> return tested to see if an EFAULT should be generated.
> Looking at include/asm-i386/uaccess.h and arch/i386/lib/usercopy.c
> I don't see how these return anything but the 3rd (length) param.

Kernel glibly copies data until a exception occurs, when that happens it
looks at the address of the faulting instruction and jumps to some fixup
code, which somehow makes the function returns the truncated value.

grep for ".section .fixup" and ".section .__ex_table." in those files.

--=20
// Gianni Tedesco (gianni at ecsc dot co dot uk)
lynx --source www.scaramanga.co.uk/gianni-at-ecsc.asc | gpg --import
8646BE7D: 6D9F 2287 870E A2C9 8F60 3A3C 91B5 7669 8646 BE7D

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