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Hallyn" , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org Subject: [RFC PATCH 5/6] security/fbfam: Detect a fork brute force attack Date: Thu, 10 Sep 2020 13:21:06 -0700 Message-Id: <20200910202107.3799376-6-keescook@chromium.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200910202107.3799376-1-keescook@chromium.org> References: <20200910202107.3799376-1-keescook@chromium.org> MIME-Version: 1.0 From: John Wood 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 --- 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 +#include 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 #include #include +#include #include +#include #include /** @@ -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; +} +