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From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Petr Mladek <pmladek@suse.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, Dmitry Vyukov <dvyukov@google.com>,
	Ondrej Mosnacek <omosnace@redhat.com>,
	Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH] twist: allow converting pr_devel()/pr_debug() into printk(KERN_DEBUG)
Date: Fri, 29 May 2020 11:04:42 +0900	[thread overview]
Message-ID: <20200529020442.GA526@jagdpanzerIV.localdomain> (raw)
In-Reply-To: <f02a71bc-0867-be60-182b-10d7377b2b04@i-love.sakura.ne.jp>

On (20/05/25 19:43), Tetsuo Handa wrote:
> >> On Sun 2020-05-24 23:50:34, Tetsuo Handa wrote:
> >>> syzbot found a NULL pointer dereference bug inside mptcp_recvmsg() due to
> >>> ssock == NULL, but this bug manifested inside selinux_socket_recvmsg()
> >>> because pr_debug() was no-op [1].
> >>>
> >>>   pr_debug("fallback-read subflow=%p",
> >>>            mptcp_subflow_ctx(ssock->sk));
> >>>   copied = sock_recvmsg(ssock, msg, flags);
> >>
> >> The NULL pointer deference was found even without this patch.
> >> This patch would just cause that it will manifest itself on another
> >> place. What is the benefit, please?
> 
> It would help localizing the bug in this specific case.
> 
> It's not only about %p, even %d can crash kernel or leak sensitive
> info (if it happens after-free/out-of-bounds/uninit). Overall it
> increases code coverage and allows to catch more bugs earlier.

I don't know. Relying on random pr_debug()-s that can be added or
removed any time. oops backtrace should help with that. You are
not going to add pr_debug() all over the kernel, are you?

	-ss

  parent reply	other threads:[~2020-05-29  2:04 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-24 14:50 [PATCH] twist: allow converting pr_devel()/pr_debug() into printk(KERN_DEBUG) Tetsuo Handa
2020-05-24 17:38 ` Joe Perches
2020-05-24 19:18   ` Ondrej Mosnacek
2020-05-25  5:03     ` Tetsuo Handa
2020-05-25  6:07       ` Joe Perches
2020-05-25  7:38         ` Dmitry Vyukov
2020-05-25  8:42 ` Petr Mladek
2020-05-25  9:11   ` Sergey Senozhatsky
2020-05-25 10:43     ` Tetsuo Handa
2020-05-27  8:37       ` Petr Mladek
2020-05-27 10:13         ` Tetsuo Handa
2020-05-27 15:55           ` Petr Mladek
2020-05-27 23:33             ` Tetsuo Handa
2020-05-28  6:56               ` [PATCH v2] twist: allow converting pr_devel()/pr_debug() into snprintf() Tetsuo Handa
2020-05-28 11:06                 ` Petr Mladek
2020-05-28 15:16                   ` Tetsuo Handa
2020-05-28 19:10                     ` Andrew Morton
2020-05-28 19:50                     ` Linus Torvalds
2020-05-28 20:01                       ` Linus Torvalds
2020-05-29  0:07                         ` Tetsuo Handa
2020-05-29  0:28                           ` Linus Torvalds
2020-05-29  2:13                             ` Tetsuo Handa
2020-05-29  2:24                               ` Linus Torvalds
2020-05-29  4:47                                 ` Tetsuo Handa
2020-05-29 13:26                                   ` Tetsuo Handa
2020-06-03 11:03                                     ` twist: allow disabling reboot request Tetsuo Handa
2020-06-03 12:44                                       ` Petr Mladek
2020-06-03 13:35                                         ` Tetsuo Handa
2020-06-04 10:21                                           ` Petr Mladek
2020-06-08  7:48                                     ` [PATCH v2] twist: allow converting pr_devel()/pr_debug() into snprintf() Dmitry Vyukov
2020-06-08 10:30                                       ` Tetsuo Handa
2020-06-08 11:31                                       ` Andrey Konovalov
2020-05-29  8:17                       ` Petr Mladek
2020-06-08 16:39                 ` Geert Uytterhoeven
2020-05-28 10:59               ` [PATCH] twist: allow converting pr_devel()/pr_debug() into printk(KERN_DEBUG) Petr Mladek
2020-05-28 11:33                 ` Tetsuo Handa
2020-05-28 12:14                   ` Petr Mladek
2020-05-28 14:13                     ` Tetsuo Handa
2020-05-28 17:08                     ` Joe Perches
2020-05-29  2:04       ` Sergey Senozhatsky [this message]
2020-05-29  5:06         ` Tetsuo Handa
2020-05-27  9:59 ` kbuild test robot
2020-05-27 13:41   ` Tetsuo Handa
2020-05-27 12:37 ` kbuild test robot

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