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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id fs24sm105321pjb.8.2020.09.10.16.14.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Sep 2020 16:14:39 -0700 (PDT) Date: Thu, 10 Sep 2020 16:14:38 -0700 From: Kees Cook To: kernel-hardening@lists.openwall.com Cc: John Wood , Matthew Wilcox , Jonathan Corbet , Alexander Viro , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Luis Chamberlain , Iurii Zaikin , James Morris , "Serge E. Hallyn" , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org Subject: Re: [RFC PATCH 4/6] security/fbfam: Add a new sysctl to control the crashing rate threshold Message-ID: <202009101612.18BAD0241D@keescook> References: <20200910202107.3799376-1-keescook@chromium.org> <20200910202107.3799376-5-keescook@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200910202107.3799376-5-keescook@chromium.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 10, 2020 at 01:21:05PM -0700, Kees Cook wrote: > From: John Wood > > This is a previous step to add the detection feature. > > A fork brute force attack will be detected when an application crashes > quickly. Since, a rate can be defined as a time per fault, add a new > sysctl to control the crashing rate threshold. > > This way, each system can tune the detection's sensibility adjusting the > milliseconds per fault. So, if the application's crashing rate falls > under this threshold an attack will be detected. So, the higher this > value, the faster an attack will be detected. > > Signed-off-by: John Wood > --- > include/fbfam/fbfam.h | 4 ++++ > kernel/sysctl.c | 9 +++++++++ > security/fbfam/Makefile | 1 + > security/fbfam/fbfam.c | 11 +++++++++++ > security/fbfam/sysctl.c | 20 ++++++++++++++++++++ > 5 files changed, 45 insertions(+) > create mode 100644 security/fbfam/sysctl.c > > diff --git a/include/fbfam/fbfam.h b/include/fbfam/fbfam.h > index b5b7d1127a52..2cfe51d2b0d5 100644 > --- a/include/fbfam/fbfam.h > +++ b/include/fbfam/fbfam.h > @@ -3,8 +3,12 @@ > #define _FBFAM_H_ > > #include > +#include > > #ifdef CONFIG_FBFAM > +#ifdef CONFIG_SYSCTL > +extern struct ctl_table fbfam_sysctls[]; > +#endif Instead of doing the extern and adding to sysctl.c, this can all be done directly (dynamically) from the fbfam.c file instead. > int fbfam_fork(struct task_struct *child); > int fbfam_execve(void); > int fbfam_exit(void); > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index 09e70ee2332e..c3b4d737bef3 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -77,6 +77,8 @@ > #include > #include > > +#include > + > #ifdef CONFIG_X86 > #include > #include > @@ -2660,6 +2662,13 @@ static struct ctl_table kern_table[] = { > .extra1 = SYSCTL_ZERO, > .extra2 = SYSCTL_ONE, > }, > +#endif > +#ifdef CONFIG_FBFAM > + { > + .procname = "fbfam", > + .mode = 0555, > + .child = fbfam_sysctls, > + }, > #endif > { } > }; > diff --git a/security/fbfam/Makefile b/security/fbfam/Makefile > index f4b9f0b19c44..b8d5751ecea4 100644 > --- a/security/fbfam/Makefile > +++ b/security/fbfam/Makefile > @@ -1,2 +1,3 @@ > # SPDX-License-Identifier: GPL-2.0 > obj-$(CONFIG_FBFAM) += fbfam.o > +obj-$(CONFIG_SYSCTL) += sysctl.o > diff --git a/security/fbfam/fbfam.c b/security/fbfam/fbfam.c > index 0387f95f6408..9be4639b72eb 100644 > --- a/security/fbfam/fbfam.c > +++ b/security/fbfam/fbfam.c > @@ -7,6 +7,17 @@ > #include > #include > > +/** > + * sysctl_crashing_rate_threshold - Crashing rate threshold. > + * > + * The rate's units are in milliseconds per fault. > + * > + * A fork brute force attack will be detected if the application's crashing rate > + * falls under this threshold. So, the higher this value, the faster an attack > + * will be detected. > + */ > +unsigned long sysctl_crashing_rate_threshold = 30000; I would move the sysctls here, instead. (Also, the above should be const.) > + > /** > * struct fbfam_stats - Fork brute force attack mitigation statistics. > * @refc: Reference counter. > diff --git a/security/fbfam/sysctl.c b/security/fbfam/sysctl.c > new file mode 100644 > index 000000000000..430323ad8e9f > --- /dev/null > +++ b/security/fbfam/sysctl.c > @@ -0,0 +1,20 @@ > +// SPDX-License-Identifier: GPL-2.0 > +#include > + > +extern unsigned long sysctl_crashing_rate_threshold; > +static unsigned long ulong_one = 1; > +static unsigned long ulong_max = ULONG_MAX; > + > +struct ctl_table fbfam_sysctls[] = { > + { > + .procname = "crashing_rate_threshold", > + .data = &sysctl_crashing_rate_threshold, > + .maxlen = sizeof(sysctl_crashing_rate_threshold), > + .mode = 0644, > + .proc_handler = proc_doulongvec_minmax, > + .extra1 = &ulong_one, > + .extra2 = &ulong_max, > + }, > + { } > +}; I wouldn't bother splitting this into a separate file. (Just leave it in fbfam.c) -- Kees Cook