1 files changed, 453 insertions, 20 deletions

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 57d4b13b631..301bbc24739 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -3,15 +3,365 @@
  *
  * Copyright 2004-2005  Andrea Arcangeli <andrea@cpushare.com>
  *
- * This defines a simple but solid secure-computing mode.
+ * Copyright (C) 2012 Google, Inc.
+ * Will Drewry <wad@chromium.org>
+ *
+ * This defines a simple but solid secure-computing facility.
+ *
+ * Mode 1 uses a fixed list of allowed system calls.
+ * Mode 2 allows user-defined system call filters in the form
+ *        of Berkeley Packet Filters/Linux Socket Filters.
  */
 
-#include <linux/seccomp.h>
-#include <linux/sched.h>
+#include <linux/atomic.h>
+#include <linux/audit.h>
 #include <linux/compat.h>
+#include <linux/sched.h>
+#include <linux/seccomp.h>
 
 /* #define SECCOMP_DEBUG 1 */
-#define NR_SECCOMP_MODES 1
+
+#ifdef CONFIG_SECCOMP_FILTER
+#include <asm/syscall.h>
+#include <linux/filter.h>
+#include <linux/ptrace.h>
+#include <linux/security.h>
+#include <linux/slab.h>
+#include <linux/tracehook.h>
+#include <linux/uaccess.h>
+
+/**
+ * struct seccomp_filter - container for seccomp BPF programs
+ *
+ * @usage: reference count to manage the object lifetime.
+ *         get/put helpers should be used when accessing an instance
+ *         outside of a lifetime-guarded section.  In general, this
+ *         is only needed for handling filters shared across tasks.
+ * @prev: points to a previously installed, or inherited, filter
+ * @len: the number of instructions in the program
+ * @insnsi: the BPF program instructions to evaluate
+ *
+ * seccomp_filter objects are organized in a tree linked via the @prev
+ * pointer.  For any task, it appears to be a singly-linked list starting
+ * with current->seccomp.filter, the most recently attached or inherited filter.
+ * However, multiple filters may share a @prev node, by way of fork(), which
+ * results in a unidirectional tree existing in memory.  This is similar to
+ * how namespaces work.
+ *
+ * seccomp_filter objects should never be modified after being attached
+ * to a task_struct (other than @usage).
+ */
+struct seccomp_filter {
+	atomic_t usage;
+	struct seccomp_filter *prev;
+	struct sk_filter *prog;
+};
+
+/* Limit any path through the tree to 256KB worth of instructions. */
+#define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter))
+
+/*
+ * Endianness is explicitly ignored and left for BPF program authors to manage
+ * as per the specific architecture.
+ */
+static void populate_seccomp_data(struct seccomp_data *sd)
+{
+	struct task_struct *task = current;
+	struct pt_regs *regs = task_pt_regs(task);
+	unsigned long args[6];
+
+	sd->nr = syscall_get_nr(task, regs);
+	sd->arch = syscall_get_arch();
+	syscall_get_arguments(task, regs, 0, 6, args);
+	sd->args[0] = args[0];
+	sd->args[1] = args[1];
+	sd->args[2] = args[2];
+	sd->args[3] = args[3];
+	sd->args[4] = args[4];
+	sd->args[5] = args[5];
+	sd->instruction_pointer = KSTK_EIP(task);
+}
+
+/**
+ *	seccomp_check_filter - verify seccomp filter code
+ *	@filter: filter to verify
+ *	@flen: length of filter
+ *
+ * Takes a previously checked filter (by sk_chk_filter) and
+ * redirects all filter code that loads struct sk_buff data
+ * and related data through seccomp_bpf_load.  It also
+ * enforces length and alignment checking of those loads.
+ *
+ * Returns 0 if the rule set is legal or -EINVAL if not.
+ */
+static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
+{
+	int pc;
+	for (pc = 0; pc < flen; pc++) {
+		struct sock_filter *ftest = &filter[pc];
+		u16 code = ftest->code;
+		u32 k = ftest->k;
+
+		switch (code) {
+		case BPF_LD | BPF_W | BPF_ABS:
+			ftest->code = BPF_LDX | BPF_W | BPF_ABS;
+			/* 32-bit aligned and not out of bounds. */
+			if (k >= sizeof(struct seccomp_data) || k & 3)
+				return -EINVAL;
+			continue;
+		case BPF_LD | BPF_W | BPF_LEN:
+			ftest->code = BPF_LD | BPF_IMM;
+			ftest->k = sizeof(struct seccomp_data);
+			continue;
+		case BPF_LDX | BPF_W | BPF_LEN:
+			ftest->code = BPF_LDX | BPF_IMM;
+			ftest->k = sizeof(struct seccomp_data);
+			continue;
+		/* Explicitly include allowed calls. */
+		case BPF_RET | BPF_K:
+		case BPF_RET | BPF_A:
+		case BPF_ALU | BPF_ADD | BPF_K:
+		case BPF_ALU | BPF_ADD | BPF_X:
+		case BPF_ALU | BPF_SUB | BPF_K:
+		case BPF_ALU | BPF_SUB | BPF_X:
+		case BPF_ALU | BPF_MUL | BPF_K:
+		case BPF_ALU | BPF_MUL | BPF_X:
+		case BPF_ALU | BPF_DIV | BPF_K:
+		case BPF_ALU | BPF_DIV | BPF_X:
+		case BPF_ALU | BPF_AND | BPF_K:
+		case BPF_ALU | BPF_AND | BPF_X:
+		case BPF_ALU | BPF_OR | BPF_K:
+		case BPF_ALU | BPF_OR | BPF_X:
+		case BPF_ALU | BPF_XOR | BPF_K:
+		case BPF_ALU | BPF_XOR | BPF_X:
+		case BPF_ALU | BPF_LSH | BPF_K:
+		case BPF_ALU | BPF_LSH | BPF_X:
+		case BPF_ALU | BPF_RSH | BPF_K:
+		case BPF_ALU | BPF_RSH | BPF_X:
+		case BPF_ALU | BPF_NEG:
+		case BPF_LD | BPF_IMM:
+		case BPF_LDX | BPF_IMM:
+		case BPF_MISC | BPF_TAX:
+		case BPF_MISC | BPF_TXA:
+		case BPF_LD | BPF_MEM:
+		case BPF_LDX | BPF_MEM:
+		case BPF_ST:
+		case BPF_STX:
+		case BPF_JMP | BPF_JA:
+		case BPF_JMP | BPF_JEQ | BPF_K:
+		case BPF_JMP | BPF_JEQ | BPF_X:
+		case BPF_JMP | BPF_JGE | BPF_K:
+		case BPF_JMP | BPF_JGE | BPF_X:
+		case BPF_JMP | BPF_JGT | BPF_K:
+		case BPF_JMP | BPF_JGT | BPF_X:
+		case BPF_JMP | BPF_JSET | BPF_K:
+		case BPF_JMP | BPF_JSET | BPF_X:
+			continue;
+		default:
+			return -EINVAL;
+		}
+	}
+	return 0;
+}
+
+/**
+ * seccomp_run_filters - evaluates all seccomp filters against @syscall
+ * @syscall: number of the current system call
+ *
+ * Returns valid seccomp BPF response codes.
+ */
+static u32 seccomp_run_filters(int syscall)
+{
+	struct seccomp_filter *f;
+	struct seccomp_data sd;
+	u32 ret = SECCOMP_RET_ALLOW;
+
+	/* Ensure unexpected behavior doesn't result in failing open. */
+	if (WARN_ON(current->seccomp.filter == NULL))
+		return SECCOMP_RET_KILL;
+
+	populate_seccomp_data(&sd);
+
+	/*
+	 * All filters in the list are evaluated and the lowest BPF return
+	 * value always takes priority (ignoring the DATA).
+	 */
+	for (f = current->seccomp.filter; f; f = f->prev) {
+		u32 cur_ret = SK_RUN_FILTER(f->prog, (void *)&sd);
+
+		if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
+			ret = cur_ret;
+	}
+	return ret;
+}
+
+/**
+ * seccomp_attach_filter: Attaches a seccomp filter to current.
+ * @fprog: BPF program to install
+ *
+ * Returns 0 on success or an errno on failure.
+ */
+static long seccomp_attach_filter(struct sock_fprog *fprog)
+{
+	struct seccomp_filter *filter;
+	unsigned long fp_size = fprog->len * sizeof(struct sock_filter);
+	unsigned long total_insns = fprog->len;
+	struct sock_filter *fp;
+	int new_len;
+	long ret;
+
+	if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
+		return -EINVAL;
+
+	for (filter = current->seccomp.filter; filter; filter = filter->prev)
+		total_insns += filter->prog->len + 4;  /* include a 4 instr penalty */
+	if (total_insns > MAX_INSNS_PER_PATH)
+		return -ENOMEM;
+
+	/*
+	 * Installing a seccomp filter requires that the task has
+	 * CAP_SYS_ADMIN in its namespace or be running with no_new_privs.
+	 * This avoids scenarios where unprivileged tasks can affect the
+	 * behavior of privileged children.
+	 */
+	if (!current->no_new_privs &&
+	    security_capable_noaudit(current_cred(), current_user_ns(),
+				     CAP_SYS_ADMIN) != 0)
+		return -EACCES;
+
+	fp = kzalloc(fp_size, GFP_KERNEL|__GFP_NOWARN);
+	if (!fp)
+		return -ENOMEM;
+
+	/* Copy the instructions from fprog. */
+	ret = -EFAULT;
+	if (copy_from_user(fp, fprog->filter, fp_size))
+		goto free_prog;
+
+	/* Check and rewrite the fprog via the skb checker */
+	ret = sk_chk_filter(fp, fprog->len);
+	if (ret)
+		goto free_prog;
+
+	/* Check and rewrite the fprog for seccomp use */
+	ret = seccomp_check_filter(fp, fprog->len);
+	if (ret)
+		goto free_prog;
+
+	/* Convert 'sock_filter' insns to 'sock_filter_int' insns */
+	ret = sk_convert_filter(fp, fprog->len, NULL, &new_len);
+	if (ret)
+		goto free_prog;
+
+	/* Allocate a new seccomp_filter */
+	ret = -ENOMEM;
+	filter = kzalloc(sizeof(struct seccomp_filter),
+			 GFP_KERNEL|__GFP_NOWARN);
+	if (!filter)
+		goto free_prog;
+
+	filter->prog = kzalloc(sk_filter_size(new_len),
+			       GFP_KERNEL|__GFP_NOWARN);
+	if (!filter->prog)
+		goto free_filter;
+
+	ret = sk_convert_filter(fp, fprog->len, filter->prog->insnsi, &new_len);
+	if (ret)
+		goto free_filter_prog;
+	kfree(fp);
+
+	atomic_set(&filter->usage, 1);
+	filter->prog->len = new_len;
+
+	sk_filter_select_runtime(filter->prog);
+
+	/*
+	 * If there is an existing filter, make it the prev and don't drop its
+	 * task reference.
+	 */
+	filter->prev = current->seccomp.filter;
+	current->seccomp.filter = filter;
+	return 0;
+
+free_filter_prog:
+	kfree(filter->prog);
+free_filter:
+	kfree(filter);
+free_prog:
+	kfree(fp);
+	return ret;
+}
+
+/**
+ * seccomp_attach_user_filter - attaches a user-supplied sock_fprog
+ * @user_filter: pointer to the user data containing a sock_fprog.
+ *
+ * Returns 0 on success and non-zero otherwise.
+ */
+static long seccomp_attach_user_filter(char __user *user_filter)
+{
+	struct sock_fprog fprog;
+	long ret = -EFAULT;
+
+#ifdef CONFIG_COMPAT
+	if (is_compat_task()) {
+		struct compat_sock_fprog fprog32;
+		if (copy_from_user(&fprog32, user_filter, sizeof(fprog32)))
+			goto out;
+		fprog.len = fprog32.len;
+		fprog.filter = compat_ptr(fprog32.filter);
+	} else /* falls through to the if below. */
+#endif
+	if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
+		goto out;
+	ret = seccomp_attach_filter(&fprog);
+out:
+	return ret;
+}
+
+/* get_seccomp_filter - increments the reference count of the filter on @tsk */
+void get_seccomp_filter(struct task_struct *tsk)
+{
+	struct seccomp_filter *orig = tsk->seccomp.filter;
+	if (!orig)
+		return;
+	/* Reference count is bounded by the number of total processes. */
+	atomic_inc(&orig->usage);
+}
+
+/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
+void put_seccomp_filter(struct task_struct *tsk)
+{
+	struct seccomp_filter *orig = tsk->seccomp.filter;
+	/* Clean up single-reference branches iteratively. */
+	while (orig && atomic_dec_and_test(&orig->usage)) {
+		struct seccomp_filter *freeme = orig;
+		orig = orig->prev;
+		sk_filter_free(freeme->prog);
+		kfree(freeme);
+	}
+}
+
+/**
+ * seccomp_send_sigsys - signals the task to allow in-process syscall emulation
+ * @syscall: syscall number to send to userland
+ * @reason: filter-supplied reason code to send to userland (via si_errno)
+ *
+ * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
+ */
+static void seccomp_send_sigsys(int syscall, int reason)
+{
+	struct siginfo info;
+	memset(&info, 0, sizeof(info));
+	info.si_signo = SIGSYS;
+	info.si_code = SYS_SECCOMP;
+	info.si_call_addr = (void __user *)KSTK_EIP(current);
+	info.si_errno = reason;
+	info.si_arch = syscall_get_arch();
+	info.si_syscall = syscall;
+	force_sig_info(SIGSYS, &info, current);
+}
+#endif	/* CONFIG_SECCOMP_FILTER */
 
 /*
  * Secure computing mode 1 allows only read/write/exit/sigreturn.
@@ -30,13 +380,15 @@ static int mode1_syscalls_32[] = {
 };
 #endif
 
-void __secure_computing(int this_syscall)
+int __secure_computing(int this_syscall)
 {
 	int mode = current->seccomp.mode;
-	int * syscall;
+	int exit_sig = 0;
+	int *syscall;
+	u32 ret;
 
 	switch (mode) {
-	case 1:
+	case SECCOMP_MODE_STRICT:
 		syscall = mode1_syscalls;
 #ifdef CONFIG_COMPAT
 		if (is_compat_task())
@@ -44,9 +396,61 @@ void __secure_computing(int this_syscall)
 #endif
 		do {
 			if (*syscall == this_syscall)
-				return;
+				return 0;
 		} while (*++syscall);
+		exit_sig = SIGKILL;
+		ret = SECCOMP_RET_KILL;
+		break;
+#ifdef CONFIG_SECCOMP_FILTER
+	case SECCOMP_MODE_FILTER: {
+		int data;
+		struct pt_regs *regs = task_pt_regs(current);
+		ret = seccomp_run_filters(this_syscall);
+		data = ret & SECCOMP_RET_DATA;
+		ret &= SECCOMP_RET_ACTION;
+		switch (ret) {
+		case SECCOMP_RET_ERRNO:
+			/* Set the low-order 16-bits as a errno. */
+			syscall_set_return_value(current, regs,
+						 -data, 0);
+			goto skip;
+		case SECCOMP_RET_TRAP:
+			/* Show the handler the original registers. */
+			syscall_rollback(current, regs);
+			/* Let the filter pass back 16 bits of data. */
+			seccomp_send_sigsys(this_syscall, data);
+			goto skip;
+		case SECCOMP_RET_TRACE:
+			/* Skip these calls if there is no tracer. */
+			if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
+				syscall_set_return_value(current, regs,
+							 -ENOSYS, 0);
+				goto skip;
+			}
+			/* Allow the BPF to provide the event message */
+			ptrace_event(PTRACE_EVENT_SECCOMP, data);
+			/*
+			 * The delivery of a fatal signal during event
+			 * notification may silently skip tracer notification.
+			 * Terminating the task now avoids executing a system
+			 * call that may not be intended.
+			 */
+			if (fatal_signal_pending(current))
+				break;
+			if (syscall_get_nr(current, regs) < 0)
+				goto skip;  /* Explicit request to skip. */
+
+			return 0;
+		case SECCOMP_RET_ALLOW:
+			return 0;
+		case SECCOMP_RET_KILL:
+		default:
+			break;
+		}
+		exit_sig = SIGSYS;
 		break;
+	}
+#endif
 	default:
 		BUG();
 	}
@@ -54,7 +458,13 @@ void __secure_computing(int this_syscall)
 #ifdef SECCOMP_DEBUG
 	dump_stack();
 #endif
-	do_exit(SIGKILL);
+	audit_seccomp(this_syscall, exit_sig, ret);
+	do_exit(exit_sig);
+#ifdef CONFIG_SECCOMP_FILTER
+skip:
+	audit_seccomp(this_syscall, exit_sig, ret);
+#endif
+	return -1;
 }
 
 long prctl_get_seccomp(void)
@@ -62,25 +472,48 @@ long prctl_get_seccomp(void)
 	return current->seccomp.mode;
 }
 
-long prctl_set_seccomp(unsigned long seccomp_mode)
+/**
+ * prctl_set_seccomp: configures current->seccomp.mode
+ * @seccomp_mode: requested mode to use
+ * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER
+ *
+ * This function may be called repeatedly with a @seccomp_mode of
+ * SECCOMP_MODE_FILTER to install additional filters.  Every filter
+ * successfully installed will be evaluated (in reverse order) for each system
+ * call the task makes.
+ *
+ * Once current->seccomp.mode is non-zero, it may not be changed.
+ *
+ * Returns 0 on success or -EINVAL on failure.
+ */
+long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
 {
-	long ret;
+	long ret = -EINVAL;
 
-	/* can set it only once to be even more secure */
-	ret = -EPERM;
-	if (unlikely(current->seccomp.mode))
+	if (current->seccomp.mode &&
+	    current->seccomp.mode != seccomp_mode)
 		goto out;
 
-	ret = -EINVAL;
-	if (seccomp_mode && seccomp_mode <= NR_SECCOMP_MODES) {
-		current->seccomp.mode = seccomp_mode;
-		set_thread_flag(TIF_SECCOMP);
+	switch (seccomp_mode) {
+	case SECCOMP_MODE_STRICT:
+		ret = 0;
 #ifdef TIF_NOTSC
 		disable_TSC();
 #endif
-		ret = 0;
+		break;
+#ifdef CONFIG_SECCOMP_FILTER
+	case SECCOMP_MODE_FILTER:
+		ret = seccomp_attach_user_filter(filter);
+		if (ret)
+			goto out;
+		break;
+#endif
+	default:
+		goto out;
 	}
 
- out:
+	current->seccomp.mode = seccomp_mode;
+	set_thread_flag(TIF_SECCOMP);
+out:
 	return ret;
 }