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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Cc: linux-arch <linux-arch@vger.kernel.org>,
	Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrey Konovalov <andreyknvl@google.com>,
	Aleksa Sarai <cyphar@cyphar.com>, Ingo Molnar <mingo@kernel.org>,
	Khalid Aziz <khalid.aziz@oracle.com>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	linux-snps-arc@lists.infradead.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC 1/4] asm-generic/uaccess: don't define inline functions if noinline lib/* in use
Date: Tue, 14 Jan 2020 13:32:50 -0800
Message-ID: <CAHk-=wjChjfOaDnGygOJpC36R6mtT7=Xf6wWTzD_wLJm=quu0Q@mail.gmail.com> (raw)
In-Reply-To: <20200114200846.29434-2-vgupta@synopsys.com>

On Tue, Jan 14, 2020 at 12:09 PM Vineet Gupta
<Vineet.Gupta1@synopsys.com> wrote:
>
> There are 2 generic varaints of strncpy_from_user() / strnlen_user()
>  (1). inline version in asm-generic/uaccess.h

I think we should get rid of this entirely. It's just a buggy garbage
implementation that nobody should ever actually use.

It does just about everything wrong that you *can* do, wrong,
including doing the NUL-filling termination of standard strncpy() that
"strncpy_from_user()" doesn't actually do.

So:

 - the asm-generic/uaccess.h __strncpy_from_user() function is just
horribly wrong

 - the generic/uaccess.h version of strncpy_from_user() shouldn't be
an inline function either, since the only thing it can do inline is
the bogus one-byte access check that _barely_ makes security work (you
also need to have a guard page to _actually_ make it work, and I'm not
atr all convinced that people do).

the whole thing is just broken and should be removed from a header file.

>  (2). optimized word-at-a-time version in lib/*

That is - outside of the original x86 strncpy_from_user() - the only
copy of this function that historically gets all the corner cases
right. And even those we've gotten wrong occasionally.

I would suggest that anybody who uses asm-generic/uaccess.h needs to
simply use the generic library version.

             Linus

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Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-14 20:08 [RFC 0/4] Switching ARC to optimized generic strncpy_from_user Vineet Gupta
2020-01-14 20:08 ` [RFC 1/4] asm-generic/uaccess: don't define inline functions if noinline lib/* in use Vineet Gupta
2020-01-14 20:57   ` Arnd Bergmann
2020-01-15 23:01     ` Vineet Gupta
2020-01-16 11:43       ` Arnd Bergmann
2020-01-14 21:32   ` Linus Torvalds [this message]
2020-01-15  9:08     ` Arnd Bergmann
2020-01-15 14:12       ` Al Viro
2020-01-15 14:21         ` Arnd Bergmann
2020-01-14 20:08 ` [RFC 2/4] lib/strncpy_from_user: Remove redundant user space pointer range check Vineet Gupta
2020-01-14 21:22   ` Linus Torvalds
2020-01-14 21:52     ` Vineet Gupta
2020-01-14 23:46     ` Al Viro
2020-01-15 14:42   ` Andrey Konovalov
2020-01-15 23:00     ` Vineet Gupta
2020-01-14 20:08 ` [RFC 3/4] ARC: uaccess: remove noinline variants of __strncpy_from_user() and friends Vineet Gupta
2020-01-14 20:08 ` [RFC 4/4] ARC: uaccess: use optimized generic __strnlen_user/__strncpy_from_user Vineet Gupta
2020-01-14 20:42   ` Arnd Bergmann
2020-01-14 21:36     ` Vineet Gupta
2020-01-14 21:49       ` Linus Torvalds
2020-01-14 22:14         ` Vineet Gupta

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