From: "Tobin C. Harding" <me@tobin.cc>
To: Jann Horn <jannh@google.com>
Cc: "Tobin C. Harding" <tobin@kernel.org>,
Kees Cook <keescook@chromium.org>, Shuah Khan <shuah@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Kernel Hardening <kernel-hardening@lists.openwall.com>,
kernel list <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@amacapital.net>
Subject: Re: [PATCH 5/6] lib: Fix function documentation for strncpy_from_user
Date: Wed, 20 Feb 2019 08:52:45 +1100 [thread overview]
Message-ID: <20190219215245.GA16094@eros.localdomain> (raw)
In-Reply-To: <CAG48ez0utQJjoJW69OwGiuH1EQtcD939-5u71ruD_1nr0eJK0g@mail.gmail.com>
On Tue, Feb 19, 2019 at 01:51:45AM +0100, Jann Horn wrote:
> +cc Andy because he's also preparing a patch for this function
>
> On Tue, Feb 19, 2019 at 12:25 AM Tobin C. Harding <tobin@kernel.org> wrote:
> > Current function documentation for strncpy_from_user() is incorrect. If
> > @count (size of destination buffer) is less than the length of the user
> > string the function does _not_ return @count but rather returns -EFAULT.
> >
> > Document correctly the function return value, also add note that string
> > may be left non-null terminated.
> >
> > Signed-off-by: Tobin C. Harding <tobin@kernel.org>
> > ---
> > lib/strncpy_from_user.c | 17 +++++++----------
> > 1 file changed, 7 insertions(+), 10 deletions(-)
> >
> > diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
> > index 58eacd41526c..11fe9a4a00fd 100644
> > --- a/lib/strncpy_from_user.c
> > +++ b/lib/strncpy_from_user.c
> > @@ -82,22 +82,19 @@ static inline long do_strncpy_from_user(char *dst, const char __user *src, long
> > }
> >
> > /**
> > - * strncpy_from_user: - Copy a NUL terminated string from userspace.
> > + * strncpy_from_user() - Copy a NUL terminated string from userspace.
> > * @dst: Destination address, in kernel space. This buffer must be at
> > * least @count bytes long.
> > * @src: Source address, in user space.
> > - * @count: Maximum number of bytes to copy, including the trailing NUL.
> > + * @count: Maximum number of bytes to copy, including the trailing %NUL.
> > *
> > * Copies a NUL-terminated string from userspace to kernel space.
> > *
> > - * On success, returns the length of the string (not including the trailing
> > - * NUL).
> > - *
> > - * If access to userspace fails, returns -EFAULT (some data may have been
> > - * copied).
> > - *
> > - * If @count is smaller than the length of the string, copies @count bytes
> > - * and returns @count.
> > + * Return: If access to userspace fails, returns -EFAULT. Otherwise,
> > + * return the number of characters copied excluding the trailing
> > + * %NUL, if the length of the user string exceeds @count return
> > + * -EFAULT (in which case @dst will be left without a %NUL
> > + * terminator).
> > */
>
> AFAICS the byte_at_a_time loop exits when max==0 is reached, and then
> if `res >= count` (in other words, if we've copied as many bytes as
> requested, haven't encountered a null byte so far, and haven't reached
> the end of the address space), we return `res`, which is the same as
> `count`. Are you sure?
Thanks for the review Jaan. Seems I was in a world of confused, I
misread count to be the size of the destination buffer not the size of
the source string.
Also, re-reading strscpy() and why its better I think I may not be the
correct person to implement strscpy_from_user() since I'm not across all
the subtleties.
If v2 seems wanted for the first patches in this set I'll drop the
*_from_user() stuff.
thanks,
Tobin.
next prev parent reply other threads:[~2019-02-19 21:52 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-18 23:23 [PATCH 0/6] lib: Add safe string funtions Tobin C. Harding
2019-02-18 23:23 ` [PATCH 1/6] lib/string: Enable string selftesting Tobin C. Harding
2019-02-19 10:55 ` Andy Shevchenko
2019-02-19 21:55 ` Tobin C. Harding
2019-02-20 10:49 ` Andy Shevchenko
2019-02-20 23:58 ` Kees Cook
2019-02-20 23:57 ` Kees Cook
2019-02-21 5:16 ` Tobin C. Harding
2019-02-18 23:23 ` [PATCH 2/6] lib/string: Fix erroneous 'overflow' documentation Tobin C. Harding
2019-02-21 0:02 ` Kees Cook
2019-02-21 5:17 ` Tobin C. Harding
2019-02-18 23:23 ` [PATCH 3/6] lib/string: Use correct docstring format Tobin C. Harding
2019-02-21 0:07 ` Kees Cook
2019-02-21 4:14 ` Randy Dunlap
2019-02-21 5:27 ` Kees Cook
2019-02-18 23:23 ` [PATCH 4/6] lib/string: Add string copy/zero function Tobin C. Harding
2019-02-21 0:48 ` Kees Cook
2019-02-21 5:20 ` Tobin C. Harding
2019-02-21 12:02 ` Andy Shevchenko
2019-02-25 20:09 ` Tobin C. Harding
2019-02-18 23:23 ` [PATCH 5/6] lib: Fix function documentation for strncpy_from_user Tobin C. Harding
2019-02-19 0:51 ` Jann Horn
2019-02-19 21:52 ` Tobin C. Harding [this message]
2019-02-21 1:05 ` Kees Cook
2019-02-21 5:24 ` Tobin C. Harding
2019-02-21 6:02 ` Kees Cook
2019-02-21 14:58 ` Rasmus Villemoes
2019-02-21 23:03 ` Kees Cook
2019-02-25 15:41 ` Rasmus Villemoes
2019-02-21 16:06 ` Jann Horn
2019-02-21 23:14 ` Kees Cook
2019-02-21 20:26 ` Stephen Rothwell
2019-02-21 23:16 ` Kees Cook
2019-02-21 14:28 ` Jann Horn
2019-02-21 22:52 ` Kees Cook
2019-02-18 23:23 ` [PATCH 6/6] lib: Add function strscpy_from_user() Tobin C. Harding
2019-02-19 2:09 ` Jann Horn
2019-02-19 2:12 ` Jann Horn
2019-02-19 21:53 ` Tobin C. Harding
2019-02-20 23:31 ` [PATCH 0/6] lib: Add safe string funtions Kees Cook
2019-02-21 5:15 ` Tobin C. Harding
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