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Message-Id: <20200910202107.3799376-6-keescook@chromium.org>
Date: Thu, 10 Sep 2020 13:21:06 -0700
From: Kees Cook <keescook@...omium.org>
To: kernel-hardening@...ts.openwall.com
Cc: Kees Cook <keescook@...omium.org>,
John Wood <john.wood@....com>,
Matthew Wilcox <willy@...radead.org>,
Jonathan Corbet <corbet@....net>,
Alexander Viro <viro@...iv.linux.org.uk>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>,
Mel Gorman <mgorman@...e.de>,
Luis Chamberlain <mcgrof@...nel.org>,
Iurii Zaikin <yzaikin@...gle.com>,
James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>,
linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org,
linux-security-module@...r.kernel.org
Subject: [RFC PATCH 5/6] security/fbfam: Detect a fork brute force attack
From: John Wood <john.wood@....com>
To detect a fork brute force attack it is necessary to compute the
crashing rate of the application. This calculation is performed in each
fatal fail of a task, or in other words, when a core dump is triggered.
If this rate shows that the application is crashing quickly, there is a
clear signal that an attack is happening.
Since the crashing rate is computed in milliseconds per fault, if this
rate goes under a certain threshold a warning is triggered.
Signed-off-by: John Wood <john.wood@....com>
---
fs/coredump.c | 2 ++
include/fbfam/fbfam.h | 2 ++
security/fbfam/fbfam.c | 39 +++++++++++++++++++++++++++++++++++++++
3 files changed, 43 insertions(+)
diff --git a/fs/coredump.c b/fs/coredump.c
index 76e7c10edfc0..d4ba4e1828d5 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -51,6 +51,7 @@
#include "internal.h"
#include <trace/events/sched.h>
+#include <fbfam/fbfam.h>
int core_uses_pid;
unsigned int core_pipe_limit;
@@ -825,6 +826,7 @@ void do_coredump(const kernel_siginfo_t *siginfo)
fail_creds:
put_cred(cred);
fail:
+ fbfam_handle_attack(siginfo->si_signo);
return;
}
diff --git a/include/fbfam/fbfam.h b/include/fbfam/fbfam.h
index 2cfe51d2b0d5..9ac8e33d8291 100644
--- a/include/fbfam/fbfam.h
+++ b/include/fbfam/fbfam.h
@@ -12,10 +12,12 @@ extern struct ctl_table fbfam_sysctls[];
int fbfam_fork(struct task_struct *child);
int fbfam_execve(void);
int fbfam_exit(void);
+int fbfam_handle_attack(int signal);
#else
static inline int fbfam_fork(struct task_struct *child) { return 0; }
static inline int fbfam_execve(void) { return 0; }
static inline int fbfam_exit(void) { return 0; }
+static inline int fbfam_handle_attack(int signal) { return 0; }
#endif
#endif /* _FBFAM_H_ */
diff --git a/security/fbfam/fbfam.c b/security/fbfam/fbfam.c
index 9be4639b72eb..3aa669e4ea51 100644
--- a/security/fbfam/fbfam.c
+++ b/security/fbfam/fbfam.c
@@ -4,7 +4,9 @@
#include <linux/errno.h>
#include <linux/gfp.h>
#include <linux/jiffies.h>
+#include <linux/printk.h>
#include <linux/refcount.h>
+#include <linux/signal.h>
#include <linux/slab.h>
/**
@@ -172,3 +174,40 @@ int fbfam_exit(void)
return 0;
}
+/**
+ * fbfam_handle_attack() - Fork brute force attack detection.
+ * @signal: Signal number that causes the core dump.
+ *
+ * The crashing rate of an application is computed in milliseconds per fault in
+ * each crash. So, if this rate goes under a certain threshold there is a clear
+ * signal that the application is crashing quickly. At this moment, a fork brute
+ * force attack is happening.
+ *
+ * Return: -EFAULT if the current task doesn't have statistical data. Zero
+ * otherwise.
+ */
+int fbfam_handle_attack(int signal)
+{
+ struct fbfam_stats *stats = current->fbfam_stats;
+ u64 delta_jiffies, delta_time;
+ u64 crashing_rate;
+
+ if (!stats)
+ return -EFAULT;
+
+ if (!(signal == SIGILL || signal == SIGBUS || signal == SIGKILL ||
+ signal == SIGSEGV || signal == SIGSYS))
+ return 0;
+
+ stats->faults += 1;
+
+ delta_jiffies = get_jiffies_64() - stats->jiffies;
+ delta_time = jiffies64_to_msecs(delta_jiffies);
+ crashing_rate = delta_time / (u64)stats->faults;
+
+ if (crashing_rate < (u64)sysctl_crashing_rate_threshold)
+ pr_warn("fbfam: Fork brute force attack detected\n");
+
+ return 0;
+}
+
--
2.25.1
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