1 files changed, 378 insertions, 18 deletions

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index e8d76c5895ea..0aeec1960f91 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -3,16 +3,343 @@
  *
  * 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/atomic.h>
 #include <linux/audit.h>
-#include <linux/seccomp.h>
-#include <linux/sched.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/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
+ * @insns: 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;
+	unsigned short len;  /* Instruction count */
+	struct sock_filter insns[];
+};
+
+/* Limit any path through the tree to 256KB worth of instructions. */
+#define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter))
+
+static void seccomp_filter_log_failure(int syscall)
+{
+	int compat = 0;
+#ifdef CONFIG_COMPAT
+	compat = is_compat_task();
+#endif
+	pr_info("%s[%d]: %ssystem call %d blocked at 0x%lx\n",
+		current->comm, task_pid_nr(current),
+		(compat ? "compat " : ""),
+		syscall, KSTK_EIP(current));
+}
+
+/**
+ * get_u32 - returns a u32 offset into data
+ * @data: a unsigned 64 bit value
+ * @index: 0 or 1 to return the first or second 32-bits
+ *
+ * This inline exists to hide the length of unsigned long.  If a 32-bit
+ * unsigned long is passed in, it will be extended and the top 32-bits will be
+ * 0. If it is a 64-bit unsigned long, then whatever data is resident will be
+ * properly returned.
+ *
+ * Endianness is explicitly ignored and left for BPF program authors to manage
+ * as per the specific architecture.
+ */
+static inline u32 get_u32(u64 data, int index)
+{
+	return ((u32 *)&data)[index];
+}
+
+/* Helper for bpf_load below. */
+#define BPF_DATA(_name) offsetof(struct seccomp_data, _name)
+/**
+ * bpf_load: checks and returns a pointer to the requested offset
+ * @off: offset into struct seccomp_data to load from
+ *
+ * Returns the requested 32-bits of data.
+ * seccomp_check_filter() should assure that @off is 32-bit aligned
+ * and not out of bounds.  Failure to do so is a BUG.
+ */
+u32 seccomp_bpf_load(int off)
+{
+	struct pt_regs *regs = task_pt_regs(current);
+	if (off == BPF_DATA(nr))
+		return syscall_get_nr(current, regs);
+	if (off == BPF_DATA(arch))
+		return syscall_get_arch(current, regs);
+	if (off >= BPF_DATA(args[0]) && off < BPF_DATA(args[6])) {
+		unsigned long value;
+		int arg = (off - BPF_DATA(args[0])) / sizeof(u64);
+		int index = !!(off % sizeof(u64));
+		syscall_get_arguments(current, regs, arg, 1, &value);
+		return get_u32(value, index);
+	}
+	if (off == BPF_DATA(instruction_pointer))
+		return get_u32(KSTK_EIP(current), 0);
+	if (off == BPF_DATA(instruction_pointer) + sizeof(u32))
+		return get_u32(KSTK_EIP(current), 1);
+	/* seccomp_check_filter should make this impossible. */
+	BUG();
+}
+
+/**
+ *	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_S_LD_W_ABS:
+			ftest->code = BPF_S_ANC_SECCOMP_LD_W;
+			/* 32-bit aligned and not out of bounds. */
+			if (k >= sizeof(struct seccomp_data) || k & 3)
+				return -EINVAL;
+			continue;
+		case BPF_S_LD_W_LEN:
+			ftest->code = BPF_S_LD_IMM;
+			ftest->k = sizeof(struct seccomp_data);
+			continue;
+		case BPF_S_LDX_W_LEN:
+			ftest->code = BPF_S_LDX_IMM;
+			ftest->k = sizeof(struct seccomp_data);
+			continue;
+		/* Explicitly include allowed calls. */
+		case BPF_S_RET_K:
+		case BPF_S_RET_A:
+		case BPF_S_ALU_ADD_K:
+		case BPF_S_ALU_ADD_X:
+		case BPF_S_ALU_SUB_K:
+		case BPF_S_ALU_SUB_X:
+		case BPF_S_ALU_MUL_K:
+		case BPF_S_ALU_MUL_X:
+		case BPF_S_ALU_DIV_X:
+		case BPF_S_ALU_AND_K:
+		case BPF_S_ALU_AND_X:
+		case BPF_S_ALU_OR_K:
+		case BPF_S_ALU_OR_X:
+		case BPF_S_ALU_LSH_K:
+		case BPF_S_ALU_LSH_X:
+		case BPF_S_ALU_RSH_K:
+		case BPF_S_ALU_RSH_X:
+		case BPF_S_ALU_NEG:
+		case BPF_S_LD_IMM:
+		case BPF_S_LDX_IMM:
+		case BPF_S_MISC_TAX:
+		case BPF_S_MISC_TXA:
+		case BPF_S_ALU_DIV_K:
+		case BPF_S_LD_MEM:
+		case BPF_S_LDX_MEM:
+		case BPF_S_ST:
+		case BPF_S_STX:
+		case BPF_S_JMP_JA:
+		case BPF_S_JMP_JEQ_K:
+		case BPF_S_JMP_JEQ_X:
+		case BPF_S_JMP_JGE_K:
+		case BPF_S_JMP_JGE_X:
+		case BPF_S_JMP_JGT_K:
+		case BPF_S_JMP_JGT_X:
+		case BPF_S_JMP_JSET_K:
+		case BPF_S_JMP_JSET_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;
+	u32 ret = SECCOMP_RET_KILL;
+	/*
+	 * All filters in the list are evaluated and the lowest BPF return
+	 * value always takes priority.
+	 */
+	for (f = current->seccomp.filter; f; f = f->prev) {
+		ret = sk_run_filter(NULL, f->insns);
+		if (ret != SECCOMP_RET_ALLOW)
+			break;
+	}
+	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;
+	long ret;
+
+	if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
+		return -EINVAL;
+
+	for (filter = current->seccomp.filter; filter; filter = filter->prev)
+		total_insns += filter->len + 4;  /* include a 4 instr penalty */
+	if (total_insns > MAX_INSNS_PER_PATH)
+		return -ENOMEM;
+
+	/*
+	 * Installing a seccomp filter requires that the task have
+	 * 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;
+
+	/* Allocate a new seccomp_filter */
+	filter = kzalloc(sizeof(struct seccomp_filter) + fp_size,
+			 GFP_KERNEL|__GFP_NOWARN);
+	if (!filter)
+		return -ENOMEM;
+	atomic_set(&filter->usage, 1);
+	filter->len = fprog->len;
+
+	/* Copy the instructions from fprog. */
+	ret = -EFAULT;
+	if (copy_from_user(filter->insns, fprog->filter, fp_size))
+		goto fail;
+
+	/* Check and rewrite the fprog via the skb checker */
+	ret = sk_chk_filter(filter->insns, filter->len);
+	if (ret)
+		goto fail;
+
+	/* Check and rewrite the fprog for seccomp use */
+	ret = seccomp_check_filter(filter->insns, filter->len);
+	if (ret)
+		goto fail;
+
+	/*
+	 * 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;
+fail:
+	kfree(filter);
+	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.
+ */
+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;
+		kfree(freeme);
+	}
+}
+#endif	/* CONFIG_SECCOMP_FILTER */
 
 /*
  * Secure computing mode 1 allows only read/write/exit/sigreturn.
@@ -34,10 +361,11 @@ static int mode1_syscalls_32[] = {
 void __secure_computing(int this_syscall)
 {
 	int mode = current->seccomp.mode;
-	int * syscall;
+	int exit_sig = 0;
+	int *syscall;
 
 	switch (mode) {
-	case 1:
+	case SECCOMP_MODE_STRICT:
 		syscall = mode1_syscalls;
 #ifdef CONFIG_COMPAT
 		if (is_compat_task())
@@ -47,7 +375,16 @@ void __secure_computing(int this_syscall)
 			if (*syscall == this_syscall)
 				return;
 		} while (*++syscall);
+		exit_sig = SIGKILL;
 		break;
+#ifdef CONFIG_SECCOMP_FILTER
+	case SECCOMP_MODE_FILTER:
+		if (seccomp_run_filters(this_syscall) == SECCOMP_RET_ALLOW)
+			return;
+		seccomp_filter_log_failure(this_syscall);
+		exit_sig = SIGSYS;
+		break;
+#endif
 	default:
 		BUG();
 	}
@@ -56,7 +393,7 @@ void __secure_computing(int this_syscall)
 	dump_stack();
 #endif
 	audit_seccomp(this_syscall);
-	do_exit(SIGKILL);
+	do_exit(exit_sig);
 }
 
 long prctl_get_seccomp(void)
@@ -64,25 +401,48 @@ 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;
 }