From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Petr Mladek <pmladek@suse.com>
Cc: "Tobin C . Harding" <me@tobin.cc>,
linux@rasmusvillemoes.dk, Joe Perches <joe@perches.com>,
linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@suse.cz>
Subject: Re: [PATCH v2 8/9] lib/vsprintf: Remove useless NULL checks
Date: Tue, 27 Feb 2018 19:35:50 +0200 [thread overview]
Message-ID: <1519752950.10722.231.camel@linux.intel.com> (raw)
In-Reply-To: <20180227155047.o74ohmoyj56up6pa@pathway.suse.cz>
On Tue, 2018-02-27 at 16:50 +0100, Petr Mladek wrote:
> On Fri 2018-02-16 23:07:10, Andy Shevchenko wrote:
> > The pointer can't be NULL since it's first what has been done in the
> > pointer().
> >
> > Remove useless checks.
> >
> > Note we leave check for !CONFIG_HAVE_CLK to make compiler
> > to optimize code away when possible.
> >
> > Cc: Petr Mladek <pmladek@suse.com>
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > ---
> > lib/vsprintf.c | 13 +------------
> > 1 file changed, 1 insertion(+), 12 deletions(-)
> >
> > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > index 97be2d07297a..a49da00b79e7 100644
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -819,10 +819,6 @@ char *hex_string(char *buf, char *end, u8
> > *addr, struct printf_spec spec,
> > /* nothing to print */
> > return buf;
> >
> > - if (ZERO_OR_NULL_PTR(addr))
>
> This macro matches also values <= 16.
Yes, I know.
This had been discussed with Rasmus and we agreed that printing a result
of kmalloc(0) is rather weird.
Moreover, in couple of cases I added these checks.
> > switch (fmt[1]) {
> > @@ -1580,9 +1572,6 @@ char *device_node_string(char *buf, char *end,
> > struct device_node *dn,
> > if (!IS_ENABLED(CONFIG_OF))
> > return string(buf, end, "(!OF)", spec);
> >
> > - if ((unsigned long)dn < PAGE_SIZE)
> > - return string(buf, end, "(null)", spec);
>
> In this case, "null" was printed for ptr < PAGE_SIZE. The same check
> is also in string() function.
Do we have a uses cases when invalid (non-NULL) pointer is supplied to
print function?
Those call sites have to be fixed.
> Note that it is not only about the printed value. The pointer is later
> derefecend. We will start crashing on dn > 0 && dn < PAGE_SIZE.
Yes.
So, fix the call sites!
> To be honest, I do not feel experienced enough to decide
> about the preferred behavior. On one hand, it is bad when
> printk() would crash the kernel. On the other hand, hiding wide
> range of values under "(null)" string might confuse people.
> Would it make sense to survive and write different strings for
> difference intervals? For example?
>
> "(null)" for ptr == 0
> "(null-16)" for ptr > 0 && ptr <= 16
> "(null-pg)" for prt > 16 && ptr <= PAGE_SIZE
>
> In each case, this patch changes the behavior and it should
> be documented in the commit message.
Personally I strongly disagree with blowing code up in such places for
little or none benefit.
--
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy
next prev parent reply other threads:[~2018-02-27 17:36 UTC|newest]
Thread overview: 87+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-16 21:07 [PATCH v2 1/9] lib/test_printf: Mark big constant with ULL Andy Shevchenko
2018-02-16 21:07 ` [PATCH v2 2/9] lib/vsprintf: Make dec_spec global Andy Shevchenko
2018-04-11 9:44 ` Petr Mladek
2018-02-16 21:07 ` [PATCH v2 3/9] lib/vsprintf: Make strspec global Andy Shevchenko
2018-04-11 9:44 ` Petr Mladek
2018-02-16 21:07 ` [PATCH v2 4/9] lib/vsprintf: Make flag_spec global Andy Shevchenko
2018-04-11 9:45 ` Petr Mladek
2018-02-16 21:07 ` [PATCH v2 5/9] lib/vsprintf: Move pointer_string() upper Andy Shevchenko
2018-04-11 9:45 ` Petr Mladek
2018-02-16 21:07 ` [PATCH v2 6/9] lib/vsprintf: Deduplicate pointer_string() Andy Shevchenko
2018-04-11 9:46 ` Petr Mladek
2018-02-16 21:07 ` [PATCH v2 7/9] lib/vsprintf: Replace space with '_' before crng is ready Andy Shevchenko
2018-02-20 2:57 ` [此邮件可能存在风险] " Yang, Shunyong
2018-04-11 9:47 ` Petr Mladek
2018-02-16 21:07 ` [PATCH v2 8/9] lib/vsprintf: Remove useless NULL checks Andy Shevchenko
2018-02-27 15:50 ` Petr Mladek
2018-02-27 17:35 ` Andy Shevchenko [this message]
2018-02-28 10:04 ` Petr Mladek
2018-02-28 10:42 ` Andy Shevchenko
2018-03-02 12:51 ` Petr Mladek
2018-03-02 12:53 ` [PATCH] vsprintf: Make "null" pointer dereference more robust Petr Mladek
2018-03-02 14:17 ` Andy Shevchenko
2018-03-05 14:53 ` Petr Mladek
2018-03-29 15:13 ` Petr Mladek
2018-03-29 16:11 ` Joe Perches
2018-03-05 15:16 ` Rasmus Villemoes
2018-03-05 15:25 ` Andy Shevchenko
2018-03-06 9:25 ` Petr Mladek
2018-03-06 9:56 ` Andy Shevchenko
2018-03-07 15:52 ` Petr Mladek
2018-03-07 18:18 ` Andy Shevchenko
2018-03-07 18:34 ` Linus Torvalds
2018-03-08 14:18 ` Petr Mladek
2018-03-08 16:45 ` Linus Torvalds
2018-03-08 17:26 ` Linus Torvalds
2018-03-09 15:01 ` Petr Mladek
2018-03-09 19:05 ` Linus Torvalds
2018-03-14 14:09 ` [PATCH v3] vsprintf: Prevent crash when dereferencing invalid pointers Petr Mladek
2018-03-14 22:12 ` Rasmus Villemoes
2018-03-15 15:07 ` Petr Mladek
2018-03-15 17:07 ` Steven Rostedt
2018-03-15 17:06 ` Steven Rostedt
2018-03-15 0:57 ` Sergey Senozhatsky
2018-03-15 7:58 ` Sergey Senozhatsky
2018-03-15 8:03 ` Sergey Senozhatsky
2018-03-15 17:01 ` Steven Rostedt
2018-03-16 1:18 ` Sergey Senozhatsky
2018-03-16 1:35 ` Linus Torvalds
2018-03-16 5:53 ` Sergey Senozhatsky
2018-03-16 8:55 ` Petr Mladek
2018-03-16 14:32 ` Steven Rostedt
2018-03-17 1:29 ` Sergey Senozhatsky
2018-03-15 13:07 ` Andy Shevchenko
2018-03-15 13:09 ` Andy Shevchenko
2018-03-15 15:26 ` Petr Mladek
2018-03-16 18:19 ` Andy Shevchenko
2018-03-29 14:53 ` Petr Mladek
2018-04-02 14:15 ` Andy Shevchenko
2018-04-03 1:12 ` Sergey Senozhatsky
2018-04-03 11:52 ` Petr Mladek
2018-04-03 11:56 ` Andy Shevchenko
2018-04-03 13:57 ` Sergey Senozhatsky
2018-04-03 11:46 ` Petr Mladek
2018-04-03 11:54 ` Andy Shevchenko
2018-04-03 13:13 ` Petr Mladek
2018-04-03 13:40 ` Andy Shevchenko
2018-04-03 14:50 ` Petr Mladek
2018-03-15 14:48 ` kbuild test robot
2018-03-15 20:26 ` kbuild test robot
2018-03-06 18:11 ` [PATCH 1/2] vsprintf: distinguish between (null), (err) and (invalid) pointer derefs Adam Borowski
2018-03-06 18:11 ` [PATCH 2/2] vsprintf: don't dereference pointers to the first or last page Adam Borowski
2018-03-07 13:22 ` Andy Shevchenko
2018-03-07 13:17 ` [PATCH 1/2] vsprintf: distinguish between (null), (err) and (invalid) pointer derefs Andy Shevchenko
2018-03-07 13:42 ` Adam Borowski
2018-03-07 13:29 ` Andy Shevchenko
2018-03-02 14:15 ` [PATCH v2 8/9] lib/vsprintf: Remove useless NULL checks Andy Shevchenko
2018-03-05 14:57 ` Petr Mladek
2018-02-28 10:44 ` Andy Shevchenko
2018-03-01 14:56 ` Andy Shevchenko
2018-02-16 21:07 ` [PATCH v2 9/9] lib/vsprintf: Mark expected switch fall-through Andy Shevchenko
2018-04-11 9:47 ` Petr Mladek
2018-02-18 12:58 ` [PATCH v2 1/9] lib/test_printf: Mark big constant with ULL Luc Van Oostenryck
2018-02-18 14:20 ` Andy Shevchenko
2018-02-19 15:24 ` Andy Shevchenko
2018-04-11 9:41 ` Petr Mladek
2018-02-18 21:52 ` Tobin C. Harding
2018-02-18 23:55 ` Andy Shevchenko
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