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@@ -3,16 +3,343 @@
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*
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* Copyright 2004-2005 Andrea Arcangeli <andrea@cpushare.com>
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*
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- * This defines a simple but solid secure-computing mode.
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+ * Copyright (C) 2012 Google, Inc.
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+ * Will Drewry <wad@chromium.org>
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+ *
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+ * This defines a simple but solid secure-computing facility.
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+ *
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+ * Mode 1 uses a fixed list of allowed system calls.
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+ * Mode 2 allows user-defined system call filters in the form
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+ * of Berkeley Packet Filters/Linux Socket Filters.
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*/
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+#include <linux/atomic.h>
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#include <linux/audit.h>
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-#include <linux/seccomp.h>
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-#include <linux/sched.h>
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#include <linux/compat.h>
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+#include <linux/sched.h>
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+#include <linux/seccomp.h>
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/* #define SECCOMP_DEBUG 1 */
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-#define NR_SECCOMP_MODES 1
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+
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+#ifdef CONFIG_SECCOMP_FILTER
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+#include <asm/syscall.h>
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+#include <linux/filter.h>
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+#include <linux/security.h>
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+#include <linux/slab.h>
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+#include <linux/tracehook.h>
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+#include <linux/uaccess.h>
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+
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+/**
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+ * struct seccomp_filter - container for seccomp BPF programs
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+ *
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+ * @usage: reference count to manage the object lifetime.
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+ * get/put helpers should be used when accessing an instance
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+ * outside of a lifetime-guarded section. In general, this
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+ * is only needed for handling filters shared across tasks.
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+ * @prev: points to a previously installed, or inherited, filter
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+ * @len: the number of instructions in the program
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+ * @insns: the BPF program instructions to evaluate
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+ *
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+ * seccomp_filter objects are organized in a tree linked via the @prev
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+ * pointer. For any task, it appears to be a singly-linked list starting
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+ * with current->seccomp.filter, the most recently attached or inherited filter.
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+ * However, multiple filters may share a @prev node, by way of fork(), which
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+ * results in a unidirectional tree existing in memory. This is similar to
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+ * how namespaces work.
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+ *
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+ * seccomp_filter objects should never be modified after being attached
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+ * to a task_struct (other than @usage).
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+ */
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+struct seccomp_filter {
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+ atomic_t usage;
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+ struct seccomp_filter *prev;
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+ unsigned short len; /* Instruction count */
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+ struct sock_filter insns[];
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+};
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+
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+/* Limit any path through the tree to 256KB worth of instructions. */
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+#define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter))
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+
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+static void seccomp_filter_log_failure(int syscall)
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+{
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+ int compat = 0;
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+#ifdef CONFIG_COMPAT
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+ compat = is_compat_task();
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+#endif
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+ pr_info("%s[%d]: %ssystem call %d blocked at 0x%lx\n",
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+ current->comm, task_pid_nr(current),
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+ (compat ? "compat " : ""),
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+ syscall, KSTK_EIP(current));
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+}
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+
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+/**
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+ * get_u32 - returns a u32 offset into data
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+ * @data: a unsigned 64 bit value
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+ * @index: 0 or 1 to return the first or second 32-bits
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+ *
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+ * This inline exists to hide the length of unsigned long. If a 32-bit
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+ * unsigned long is passed in, it will be extended and the top 32-bits will be
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+ * 0. If it is a 64-bit unsigned long, then whatever data is resident will be
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+ * properly returned.
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+ *
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+ * Endianness is explicitly ignored and left for BPF program authors to manage
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+ * as per the specific architecture.
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+ */
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+static inline u32 get_u32(u64 data, int index)
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+{
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+ return ((u32 *)&data)[index];
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+}
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+
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+/* Helper for bpf_load below. */
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+#define BPF_DATA(_name) offsetof(struct seccomp_data, _name)
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+/**
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+ * bpf_load: checks and returns a pointer to the requested offset
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+ * @off: offset into struct seccomp_data to load from
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+ *
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+ * Returns the requested 32-bits of data.
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+ * seccomp_check_filter() should assure that @off is 32-bit aligned
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+ * and not out of bounds. Failure to do so is a BUG.
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+ */
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+u32 seccomp_bpf_load(int off)
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+{
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+ struct pt_regs *regs = task_pt_regs(current);
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+ if (off == BPF_DATA(nr))
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+ return syscall_get_nr(current, regs);
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+ if (off == BPF_DATA(arch))
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+ return syscall_get_arch(current, regs);
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+ if (off >= BPF_DATA(args[0]) && off < BPF_DATA(args[6])) {
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+ unsigned long value;
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+ int arg = (off - BPF_DATA(args[0])) / sizeof(u64);
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+ int index = !!(off % sizeof(u64));
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+ syscall_get_arguments(current, regs, arg, 1, &value);
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+ return get_u32(value, index);
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+ }
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+ if (off == BPF_DATA(instruction_pointer))
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+ return get_u32(KSTK_EIP(current), 0);
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+ if (off == BPF_DATA(instruction_pointer) + sizeof(u32))
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+ return get_u32(KSTK_EIP(current), 1);
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+ /* seccomp_check_filter should make this impossible. */
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+ BUG();
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+}
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+
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+/**
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+ * seccomp_check_filter - verify seccomp filter code
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+ * @filter: filter to verify
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+ * @flen: length of filter
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+ *
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+ * Takes a previously checked filter (by sk_chk_filter) and
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+ * redirects all filter code that loads struct sk_buff data
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+ * and related data through seccomp_bpf_load. It also
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+ * enforces length and alignment checking of those loads.
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+ *
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+ * Returns 0 if the rule set is legal or -EINVAL if not.
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+ */
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+static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
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+{
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+ int pc;
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+ for (pc = 0; pc < flen; pc++) {
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+ struct sock_filter *ftest = &filter[pc];
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+ u16 code = ftest->code;
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+ u32 k = ftest->k;
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+
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+ switch (code) {
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+ case BPF_S_LD_W_ABS:
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+ ftest->code = BPF_S_ANC_SECCOMP_LD_W;
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+ /* 32-bit aligned and not out of bounds. */
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+ if (k >= sizeof(struct seccomp_data) || k & 3)
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+ return -EINVAL;
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+ continue;
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+ case BPF_S_LD_W_LEN:
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+ ftest->code = BPF_S_LD_IMM;
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+ ftest->k = sizeof(struct seccomp_data);
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+ continue;
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+ case BPF_S_LDX_W_LEN:
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+ ftest->code = BPF_S_LDX_IMM;
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+ ftest->k = sizeof(struct seccomp_data);
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+ continue;
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+ /* Explicitly include allowed calls. */
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+ case BPF_S_RET_K:
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+ case BPF_S_RET_A:
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+ case BPF_S_ALU_ADD_K:
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+ case BPF_S_ALU_ADD_X:
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+ case BPF_S_ALU_SUB_K:
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+ case BPF_S_ALU_SUB_X:
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+ case BPF_S_ALU_MUL_K:
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+ case BPF_S_ALU_MUL_X:
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+ case BPF_S_ALU_DIV_X:
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+ case BPF_S_ALU_AND_K:
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+ case BPF_S_ALU_AND_X:
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+ case BPF_S_ALU_OR_K:
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+ case BPF_S_ALU_OR_X:
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+ case BPF_S_ALU_LSH_K:
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+ case BPF_S_ALU_LSH_X:
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+ case BPF_S_ALU_RSH_K:
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+ case BPF_S_ALU_RSH_X:
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+ case BPF_S_ALU_NEG:
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+ case BPF_S_LD_IMM:
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+ case BPF_S_LDX_IMM:
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+ case BPF_S_MISC_TAX:
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+ case BPF_S_MISC_TXA:
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+ case BPF_S_ALU_DIV_K:
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+ case BPF_S_LD_MEM:
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+ case BPF_S_LDX_MEM:
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+ case BPF_S_ST:
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+ case BPF_S_STX:
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+ case BPF_S_JMP_JA:
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+ case BPF_S_JMP_JEQ_K:
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+ case BPF_S_JMP_JEQ_X:
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+ case BPF_S_JMP_JGE_K:
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+ case BPF_S_JMP_JGE_X:
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+ case BPF_S_JMP_JGT_K:
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+ case BPF_S_JMP_JGT_X:
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+ case BPF_S_JMP_JSET_K:
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+ case BPF_S_JMP_JSET_X:
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+ continue;
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+ default:
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+ return -EINVAL;
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+ }
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+ }
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+ return 0;
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+}
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+
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+/**
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+ * seccomp_run_filters - evaluates all seccomp filters against @syscall
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+ * @syscall: number of the current system call
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+ *
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+ * Returns valid seccomp BPF response codes.
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+ */
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+static u32 seccomp_run_filters(int syscall)
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+{
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+ struct seccomp_filter *f;
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+ u32 ret = SECCOMP_RET_KILL;
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+ /*
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+ * All filters in the list are evaluated and the lowest BPF return
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+ * value always takes priority.
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+ */
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+ for (f = current->seccomp.filter; f; f = f->prev) {
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+ ret = sk_run_filter(NULL, f->insns);
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+ if (ret != SECCOMP_RET_ALLOW)
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+ break;
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+ }
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+ return ret;
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+}
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+
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+/**
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+ * seccomp_attach_filter: Attaches a seccomp filter to current.
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+ * @fprog: BPF program to install
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+ *
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+ * Returns 0 on success or an errno on failure.
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+ */
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+static long seccomp_attach_filter(struct sock_fprog *fprog)
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+{
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+ struct seccomp_filter *filter;
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+ unsigned long fp_size = fprog->len * sizeof(struct sock_filter);
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+ unsigned long total_insns = fprog->len;
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+ long ret;
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+
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+ if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
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+ return -EINVAL;
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+
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+ for (filter = current->seccomp.filter; filter; filter = filter->prev)
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+ total_insns += filter->len + 4; /* include a 4 instr penalty */
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+ if (total_insns > MAX_INSNS_PER_PATH)
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+ return -ENOMEM;
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+
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+ /*
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+ * Installing a seccomp filter requires that the task have
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+ * CAP_SYS_ADMIN in its namespace or be running with no_new_privs.
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+ * This avoids scenarios where unprivileged tasks can affect the
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+ * behavior of privileged children.
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+ */
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+ if (!current->no_new_privs &&
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+ security_capable_noaudit(current_cred(), current_user_ns(),
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+ CAP_SYS_ADMIN) != 0)
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+ return -EACCES;
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+
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+ /* Allocate a new seccomp_filter */
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+ filter = kzalloc(sizeof(struct seccomp_filter) + fp_size,
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+ GFP_KERNEL|__GFP_NOWARN);
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+ if (!filter)
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+ return -ENOMEM;
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+ atomic_set(&filter->usage, 1);
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+ filter->len = fprog->len;
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+
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+ /* Copy the instructions from fprog. */
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+ ret = -EFAULT;
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+ if (copy_from_user(filter->insns, fprog->filter, fp_size))
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+ goto fail;
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+
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+ /* Check and rewrite the fprog via the skb checker */
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+ ret = sk_chk_filter(filter->insns, filter->len);
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+ if (ret)
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+ goto fail;
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+
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+ /* Check and rewrite the fprog for seccomp use */
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+ ret = seccomp_check_filter(filter->insns, filter->len);
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+ if (ret)
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+ goto fail;
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+
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+ /*
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+ * If there is an existing filter, make it the prev and don't drop its
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+ * task reference.
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+ */
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+ filter->prev = current->seccomp.filter;
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+ current->seccomp.filter = filter;
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+ return 0;
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+fail:
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+ kfree(filter);
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+ return ret;
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+}
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+
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+/**
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+ * seccomp_attach_user_filter - attaches a user-supplied sock_fprog
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+ * @user_filter: pointer to the user data containing a sock_fprog.
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+ *
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+ * Returns 0 on success and non-zero otherwise.
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+ */
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+long seccomp_attach_user_filter(char __user *user_filter)
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+{
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+ struct sock_fprog fprog;
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+ long ret = -EFAULT;
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+
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+#ifdef CONFIG_COMPAT
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+ if (is_compat_task()) {
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+ struct compat_sock_fprog fprog32;
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+ if (copy_from_user(&fprog32, user_filter, sizeof(fprog32)))
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+ goto out;
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+ fprog.len = fprog32.len;
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+ fprog.filter = compat_ptr(fprog32.filter);
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+ } else /* falls through to the if below. */
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+#endif
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+ if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
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+ goto out;
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+ ret = seccomp_attach_filter(&fprog);
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+out:
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+ return ret;
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+}
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+
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+/* get_seccomp_filter - increments the reference count of the filter on @tsk */
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+void get_seccomp_filter(struct task_struct *tsk)
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+{
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+ struct seccomp_filter *orig = tsk->seccomp.filter;
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+ if (!orig)
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+ return;
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+ /* Reference count is bounded by the number of total processes. */
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+ atomic_inc(&orig->usage);
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+}
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+
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+/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
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+void put_seccomp_filter(struct task_struct *tsk)
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+{
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+ struct seccomp_filter *orig = tsk->seccomp.filter;
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+ /* Clean up single-reference branches iteratively. */
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+ while (orig && atomic_dec_and_test(&orig->usage)) {
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+ struct seccomp_filter *freeme = orig;
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+ orig = orig->prev;
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+ kfree(freeme);
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+ }
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+}
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+#endif /* CONFIG_SECCOMP_FILTER */
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/*
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* Secure computing mode 1 allows only read/write/exit/sigreturn.
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@@ -34,10 +361,11 @@ static int mode1_syscalls_32[] = {
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void __secure_computing(int this_syscall)
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{
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int mode = current->seccomp.mode;
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- int * syscall;
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+ int exit_sig = 0;
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+ int *syscall;
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switch (mode) {
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- case 1:
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+ case SECCOMP_MODE_STRICT:
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syscall = mode1_syscalls;
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#ifdef CONFIG_COMPAT
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if (is_compat_task())
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@@ -47,7 +375,16 @@ void __secure_computing(int this_syscall)
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if (*syscall == this_syscall)
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return;
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} while (*++syscall);
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+ exit_sig = SIGKILL;
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break;
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+#ifdef CONFIG_SECCOMP_FILTER
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+ case SECCOMP_MODE_FILTER:
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+ if (seccomp_run_filters(this_syscall) == SECCOMP_RET_ALLOW)
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+ return;
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+ seccomp_filter_log_failure(this_syscall);
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+ exit_sig = SIGSYS;
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+ break;
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+#endif
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default:
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BUG();
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}
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@@ -56,7 +393,7 @@ void __secure_computing(int this_syscall)
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dump_stack();
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#endif
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audit_seccomp(this_syscall);
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- do_exit(SIGKILL);
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+ do_exit(exit_sig);
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}
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long prctl_get_seccomp(void)
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@@ -64,25 +401,48 @@ long prctl_get_seccomp(void)
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return current->seccomp.mode;
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}
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-long prctl_set_seccomp(unsigned long seccomp_mode)
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+/**
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+ * 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;
|
|
|
}
|
Will Drewry