/* * 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>#include <linux/slab.h>#include <linux/syscalls.h> #ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER#include <asm/syscall.h>#endif #ifdef CONFIG_SECCOMP_FILTER#include <linux/filter.h>#include <linux/pid.h>#include <linux/ptrace.h>#include <linux/security.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 bpf_prog *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 bpf_check_classic) 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(struct seccomp_data *sd){ struct seccomp_data sd_local; u32 ret = SECCOMP_RET_ALLOW; /* Make sure cross-thread synced filter points somewhere sane. */ struct seccomp_filter *f = lockless_dereference(current->seccomp.filter); /* Ensure unexpected behavior doesn't result in failing open. */ if (unlikely(WARN_ON(f == NULL))) return SECCOMP_RET_KILL; if (!sd) { populate_seccomp_data(&sd_local); sd = &sd_local; } /* * All filters in the list are evaluated and the lowest BPF return * value always takes priority (ignoring the DATA). */ for (; f; f = f->prev) { u32 cur_ret = BPF_PROG_RUN(f->prog, (void *)sd); if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION)) ret = cur_ret; } return ret;}#endif /* CONFIG_SECCOMP_FILTER */ static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode){ assert_spin_locked(¤t->sighand->siglock); if (current->seccomp.mode && current->seccomp.mode != seccomp_mode) return false; return true;} static inline void seccomp_assign_mode(struct task_struct *task, unsigned long seccomp_mode){ assert_spin_locked(&task->sighand->siglock); task->seccomp.mode = seccomp_mode; /* * Make sure TIF_SECCOMP cannot be set before the mode (and * filter) is set. */ smp_mb__before_atomic(); set_tsk_thread_flag(task, TIF_SECCOMP);} #ifdef CONFIG_SECCOMP_FILTER/* Returns 1 if the parent is an ancestor of the child. */static int is_ancestor(struct seccomp_filter *parent, struct seccomp_filter *child){ /* NULL is the root ancestor. */ if (parent == NULL) return 1; for (; child; child = child->prev) if (child == parent) return 1; return 0;} /** * seccomp_can_sync_threads: checks if all threads can be synchronized * * Expects sighand and cred_guard_mutex locks to be held. * * Returns 0 on success, -ve on error, or the pid of a thread which was * either not in the correct seccomp mode or it did not have an ancestral * seccomp filter. */static inline pid_t seccomp_can_sync_threads(void){ struct task_struct *thread, *caller; BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); assert_spin_locked(¤t->sighand->siglock); /* Validate all threads being eligible for synchronization. */ caller = current; for_each_thread(caller, thread) { pid_t failed; /* Skip current, since it is initiating the sync. */ if (thread == caller) continue; if (thread->seccomp.mode == SECCOMP_MODE_DISABLED || (thread->seccomp.mode == SECCOMP_MODE_FILTER && is_ancestor(thread->seccomp.filter, caller->seccomp.filter))) continue; /* Return the first thread that cannot be synchronized. */ failed = task_pid_vnr(thread); /* If the pid cannot be resolved, then return -ESRCH */ if (unlikely(WARN_ON(failed == 0))) failed = -ESRCH; return failed; } return 0;} /** * seccomp_sync_threads: sets all threads to use current's filter * * Expects sighand and cred_guard_mutex locks to be held, and for * seccomp_can_sync_threads() to have returned success already * without dropping the locks. * */static inline void seccomp_sync_threads(void){ struct task_struct *thread, *caller; BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); assert_spin_locked(¤t->sighand->siglock); /* Synchronize all threads. */ caller = current; for_each_thread(caller, thread) { /* Skip current, since it needs no changes. */ if (thread == caller) continue; /* Get a task reference for the new leaf node. */ get_seccomp_filter(caller); /* * Drop the task reference to the shared ancestor since * current's path will hold a reference. (This also * allows a put before the assignment.) */ put_seccomp_filter(thread); smp_store_release(&thread->seccomp.filter, caller->seccomp.filter); /* * Don't let an unprivileged task work around * the no_new_privs restriction by creating * a thread that sets it up, enters seccomp, * then dies. */ if (task_no_new_privs(caller)) task_set_no_new_privs(thread); /* * Opt the other thread into seccomp if needed. * As threads are considered to be trust-realm * equivalent (see ptrace_may_access), it is safe to * allow one thread to transition the other. */ if (thread->seccomp.mode == SECCOMP_MODE_DISABLED) seccomp_assign_mode(thread, SECCOMP_MODE_FILTER); }} /** * seccomp_prepare_filter: Prepares a seccomp filter for use. * @fprog: BPF program to install * * Returns filter on success or an ERR_PTR on failure. */static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog){ struct seccomp_filter *sfilter; int ret; const bool save_orig = config_enabled(CONFIG_CHECKPOINT_RESTORE); if (fprog->len == 0 || fprog->len > BPF_MAXINSNS) return ERR_PTR(-EINVAL); BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter)); /* * 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 (!task_no_new_privs(current) && security_capable_noaudit(current_cred(), current_user_ns(), CAP_SYS_ADMIN) != 0) return ERR_PTR(-EACCES); /* Allocate a new seccomp_filter */ sfilter = kzalloc(sizeof(*sfilter), GFP_KERNEL | __GFP_NOWARN); if (!sfilter) return ERR_PTR(-ENOMEM); ret = bpf_prog_create_from_user(&sfilter->prog, fprog, seccomp_check_filter, save_orig); if (ret < 0) { kfree(sfilter); return ERR_PTR(ret); } atomic_set(&sfilter->usage, 1); return sfilter;} /** * seccomp_prepare_user_filter - prepares 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 struct seccomp_filter *seccomp_prepare_user_filter(const char __user *user_filter){ struct sock_fprog fprog; struct seccomp_filter *filter = ERR_PTR(-EFAULT); #ifdef CONFIG_COMPAT if (in_compat_syscall()) { 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; filter = seccomp_prepare_filter(&fprog);out: return filter;} /** * seccomp_attach_filter: validate and attach filter * @flags: flags to change filter behavior * @filter: seccomp filter to add to the current process * * Caller must be holding current->sighand->siglock lock. * * Returns 0 on success, -ve on error. */static long seccomp_attach_filter(unsigned int flags, struct seccomp_filter *filter){ unsigned long total_insns; struct seccomp_filter *walker; assert_spin_locked(¤t->sighand->siglock); /* Validate resulting filter length. */ total_insns = filter->prog->len; for (walker = current->seccomp.filter; walker; walker = walker->prev) total_insns += walker->prog->len + 4; /* 4 instr penalty */ if (total_insns > MAX_INSNS_PER_PATH) return -ENOMEM; /* If thread sync has been requested, check that it is possible. */ if (flags & SECCOMP_FILTER_FLAG_TSYNC) { int ret; ret = seccomp_can_sync_threads(); if (ret) return ret; } /* * 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; /* Now that the new filter is in place, synchronize to all threads. */ if (flags & SECCOMP_FILTER_FLAG_TSYNC) seccomp_sync_threads(); return 0;} /* 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);} static inline void seccomp_filter_free(struct seccomp_filter *filter){ if (filter) { bpf_prog_destroy(filter->prog); kfree(filter); }} /* 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; seccomp_filter_free(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));Lines 1–500 of 943. 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/* * 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> #include <linux/slab.h> #include <linux/syscalls.h> #ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER #include <asm/syscall.h> #endif #ifdef CONFIG_SECCOMP_FILTER #include <linux/filter.h> #include <linux/pid.h> #include <linux/ptrace.h> #include <linux/security.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 bpf_prog *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 bpf_check_classic) 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(struct seccomp_data *sd) { struct seccomp_data sd_local; u32 ret = SECCOMP_RET_ALLOW; /* Make sure cross-thread synced filter points somewhere sane. */ struct seccomp_filter *f = lockless_dereference(current->seccomp.filter); /* Ensure unexpected behavior doesn't result in failing open. */ if (unlikely(WARN_ON(f == NULL))) return SECCOMP_RET_KILL; if (!sd) { populate_seccomp_data(&sd_local); sd = &sd_local; } /* * All filters in the list are evaluated and the lowest BPF return * value always takes priority (ignoring the DATA). */ for (; f; f = f->prev) { u32 cur_ret = BPF_PROG_RUN(f->prog, (void *)sd); if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION)) ret = cur_ret; } return ret; } #endif /* CONFIG_SECCOMP_FILTER */ static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode) { assert_spin_locked(¤t->sighand->siglock); if (current->seccomp.mode && current->seccomp.mode != seccomp_mode) return false; return true; } static inline void seccomp_assign_mode(struct task_struct *task, unsigned long seccomp_mode) { assert_spin_locked(&task->sighand->siglock); task->seccomp.mode = seccomp_mode; /* * Make sure TIF_SECCOMP cannot be set before the mode (and * filter) is set. */ smp_mb__before_atomic(); set_tsk_thread_flag(task, TIF_SECCOMP); } #ifdef CONFIG_SECCOMP_FILTER /* Returns 1 if the parent is an ancestor of the child. */ static int is_ancestor(struct seccomp_filter *parent, struct seccomp_filter *child) { /* NULL is the root ancestor. */ if (parent == NULL) return 1; for (; child; child = child->prev) if (child == parent) return 1; return 0; } /** * seccomp_can_sync_threads: checks if all threads can be synchronized * * Expects sighand and cred_guard_mutex locks to be held. * * Returns 0 on success, -ve on error, or the pid of a thread which was * either not in the correct seccomp mode or it did not have an ancestral * seccomp filter. */ static inline pid_t seccomp_can_sync_threads(void) { struct task_struct *thread, *caller; BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); assert_spin_locked(¤t->sighand->siglock); /* Validate all threads being eligible for synchronization. */ caller = current; for_each_thread(caller, thread) { pid_t failed; /* Skip current, since it is initiating the sync. */ if (thread == caller) continue; if (thread->seccomp.mode == SECCOMP_MODE_DISABLED || (thread->seccomp.mode == SECCOMP_MODE_FILTER && is_ancestor(thread->seccomp.filter, caller->seccomp.filter))) continue; /* Return the first thread that cannot be synchronized. */ failed = task_pid_vnr(thread); /* If the pid cannot be resolved, then return -ESRCH */ if (unlikely(WARN_ON(failed == 0))) failed = -ESRCH; return failed; } return 0; } /** * seccomp_sync_threads: sets all threads to use current's filter * * Expects sighand and cred_guard_mutex locks to be held, and for * seccomp_can_sync_threads() to have returned success already * without dropping the locks. * */ static inline void seccomp_sync_threads(void) { struct task_struct *thread, *caller; BUG_ON(!mutex_is_locked(¤t->signal->cred_guard_mutex)); assert_spin_locked(¤t->sighand->siglock); /* Synchronize all threads. */ caller = current; for_each_thread(caller, thread) { /* Skip current, since it needs no changes. */ if (thread == caller) continue; /* Get a task reference for the new leaf node. */ get_seccomp_filter(caller); /* * Drop the task reference to the shared ancestor since * current's path will hold a reference. (This also * allows a put before the assignment.) */ put_seccomp_filter(thread); smp_store_release(&thread->seccomp.filter, caller->seccomp.filter); /* * Don't let an unprivileged task work around * the no_new_privs restriction by creating * a thread that sets it up, enters seccomp, * then dies. */ if (task_no_new_privs(caller)) task_set_no_new_privs(thread); /* * Opt the other thread into seccomp if needed. * As threads are considered to be trust-realm * equivalent (see ptrace_may_access), it is safe to * allow one thread to transition the other. */ if (thread->seccomp.mode == SECCOMP_MODE_DISABLED) seccomp_assign_mode(thread, SECCOMP_MODE_FILTER); } } /** * seccomp_prepare_filter: Prepares a seccomp filter for use. * @fprog: BPF program to install * * Returns filter on success or an ERR_PTR on failure. */ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) { struct seccomp_filter *sfilter; int ret; const bool save_orig = config_enabled(CONFIG_CHECKPOINT_RESTORE); if (fprog->len == 0 || fprog->len > BPF_MAXINSNS) return ERR_PTR(-EINVAL); BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter)); /* * 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 (!task_no_new_privs(current) && security_capable_noaudit(current_cred(), current_user_ns(), CAP_SYS_ADMIN) != 0) return ERR_PTR(-EACCES); /* Allocate a new seccomp_filter */ sfilter = kzalloc(sizeof(*sfilter), GFP_KERNEL | __GFP_NOWARN); if (!sfilter) return ERR_PTR(-ENOMEM); ret = bpf_prog_create_from_user(&sfilter->prog, fprog, seccomp_check_filter, save_orig); if (ret < 0) { kfree(sfilter); return ERR_PTR(ret); } atomic_set(&sfilter->usage, 1); return sfilter; } /** * seccomp_prepare_user_filter - prepares 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 struct seccomp_filter * seccomp_prepare_user_filter(const char __user *user_filter) { struct sock_fprog fprog; struct seccomp_filter *filter = ERR_PTR(-EFAULT); #ifdef CONFIG_COMPAT if (in_compat_syscall()) { 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; filter = seccomp_prepare_filter(&fprog); out: return filter; } /** * seccomp_attach_filter: validate and attach filter * @flags: flags to change filter behavior * @filter: seccomp filter to add to the current process * * Caller must be holding current->sighand->siglock lock. * * Returns 0 on success, -ve on error. */ static long seccomp_attach_filter(unsigned int flags, struct seccomp_filter *filter) { unsigned long total_insns; struct seccomp_filter *walker; assert_spin_locked(¤t->sighand->siglock); /* Validate resulting filter length. */ total_insns = filter->prog->len; for (walker = current->seccomp.filter; walker; walker = walker->prev) total_insns += walker->prog->len + 4; /* 4 instr penalty */ if (total_insns > MAX_INSNS_PER_PATH) return -ENOMEM; /* If thread sync has been requested, check that it is possible. */ if (flags & SECCOMP_FILTER_FLAG_TSYNC) { int ret; ret = seccomp_can_sync_threads(); if (ret) return ret; } /* * 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; /* Now that the new filter is in place, synchronize to all threads. */ if (flags & SECCOMP_FILTER_FLAG_TSYNC) seccomp_sync_threads(); return 0; } /* 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); } static inline void seccomp_filter_free(struct seccomp_filter *filter) { if (filter) { bpf_prog_destroy(filter->prog); kfree(filter); } } /* 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; seccomp_filter_free(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));