| /* |
| * linux/kernel/seccomp.c |
| * |
| * Copyright 2004-2005 Andrea Arcangeli <andrea@cpushare.com> |
| * |
| * 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/compat.h> |
| #include <linux/sched.h> |
| #include <linux/seccomp.h> |
| |
| /* #define SECCOMP_DEBUG 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)) |
| |
| /** |
| * 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_ALLOW; |
| |
| /* Ensure unexpected behavior doesn't result in failing open. */ |
| if (WARN_ON(current->seccomp.filter == NULL)) |
| return SECCOMP_RET_KILL; |
| |
| /* |
| * 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(NULL, f->insns); |
| 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; |
| 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); |
| } |
| } |
| |
| /** |
| * 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(current, task_pt_regs(current)); |
| info.si_syscall = syscall; |
| force_sig_info(SIGSYS, &info, current); |
| } |
| #endif /* CONFIG_SECCOMP_FILTER */ |
| |
| /* |
| * Secure computing mode 1 allows only read/write/exit/sigreturn. |
| * To be fully secure this must be combined with rlimit |
| * to limit the stack allocations too. |
| */ |
| static int mode1_syscalls[] = { |
| __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn, |
| 0, /* null terminated */ |
| }; |
| |
| #ifdef CONFIG_COMPAT |
| static int mode1_syscalls_32[] = { |
| __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32, |
| 0, /* null terminated */ |
| }; |
| #endif |
| |
| int __secure_computing(int this_syscall) |
| { |
| int mode = current->seccomp.mode; |
| int exit_sig = 0; |
| int *syscall; |
| u32 ret = SECCOMP_RET_KILL; |
| int data; |
| |
| switch (mode) { |
| case SECCOMP_MODE_STRICT: |
| syscall = mode1_syscalls; |
| #ifdef CONFIG_COMPAT |
| if (is_compat_task()) |
| syscall = mode1_syscalls_32; |
| #endif |
| do { |
| if (*syscall == this_syscall) |
| return 0; |
| } while (*++syscall); |
| exit_sig = SIGKILL; |
| break; |
| #ifdef CONFIG_SECCOMP_FILTER |
| case SECCOMP_MODE_FILTER: |
| ret = seccomp_run_filters(this_syscall); |
| data = ret & SECCOMP_RET_DATA; |
| switch (ret & SECCOMP_RET_ACTION) { |
| case SECCOMP_RET_ERRNO: |
| /* Set the low-order 16-bits as a errno. */ |
| syscall_set_return_value(current, task_pt_regs(current), |
| -data, 0); |
| goto skip; |
| case SECCOMP_RET_TRAP: |
| /* Show the handler the original registers. */ |
| syscall_rollback(current, task_pt_regs(current)); |
| /* Let the filter pass back 16 bits of data. */ |
| seccomp_send_sigsys(this_syscall, data); |
| goto skip; |
| case SECCOMP_RET_ALLOW: |
| return 0; |
| case SECCOMP_RET_KILL: |
| default: |
| break; |
| } |
| exit_sig = SIGSYS; |
| break; |
| #endif |
| default: |
| BUG(); |
| } |
| |
| #ifdef SECCOMP_DEBUG |
| dump_stack(); |
| #endif |
| audit_seccomp(this_syscall, exit_sig, ret); |
| do_exit(exit_sig); |
| skip: |
| audit_seccomp(this_syscall, exit_sig, ret); |
| return -1; |
| } |
| |
| long prctl_get_seccomp(void) |
| { |
| return current->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 = -EINVAL; |
| |
| if (current->seccomp.mode && |
| current->seccomp.mode != seccomp_mode) |
| goto out; |
| |
| switch (seccomp_mode) { |
| case SECCOMP_MODE_STRICT: |
| ret = 0; |
| #ifdef TIF_NOTSC |
| disable_TSC(); |
| #endif |
| break; |
| #ifdef CONFIG_SECCOMP_FILTER |
| case SECCOMP_MODE_FILTER: |
| ret = seccomp_attach_user_filter(filter); |
| if (ret) |
| goto out; |
| break; |
| #endif |
| default: |
| goto out; |
| } |
| |
| current->seccomp.mode = seccomp_mode; |
| set_thread_flag(TIF_SECCOMP); |
| out: |
| return ret; |
| } |