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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213// SPDX-License-Identifier: BSD-3-Clause/* * Very simple script interpreter that can evaluate two different commands (one * per line): * - "?" to initialize a counter from user's input; * - "+" to increment the counter (which is set to 0 by default). * * See tools/testing/selftests/exec/check-exec-tests.sh and * Documentation/userspace-api/check_exec.rst * * Copyright © 2024 Microsoft Corporation */
#define _GNU_SOURCE#include <errno.h>#include <linux/fcntl.h>#include <linux/prctl.h>#include <linux/securebits.h>#include <stdbool.h>#include <stdio.h>#include <stdlib.h>#include <string.h>#include <sys/prctl.h>#include <sys/syscall.h>#include <unistd.h>
static int sys_execveat(int dirfd, const char *pathname, char *const argv[], char *const envp[], int flags){ return syscall(__NR_execveat, dirfd, pathname, argv, envp, flags);}
/* Returns 1 on error, 0 otherwise. */static int interpret_buffer(char *buffer, size_t buffer_size){ char *line, *saveptr = NULL; long long number = 0;
/* Each command is the first character of a line. */ saveptr = NULL; line = strtok_r(buffer, "\n", &saveptr); while (line) { if (*line != '#' && strlen(line) != 1) { fprintf(stderr, "# ERROR: Unknown string\n"); return 1; } switch (*line) { case '#': /* Skips shebang and comments. */ break; case '+': /* Increments and prints the number. */ number++; printf("%lld\n", number); break; case '?': /* Reads integer from stdin. */ fprintf(stderr, "> Enter new number: \n"); if (scanf("%lld", &number) != 1) { fprintf(stderr, "# WARNING: Failed to read number from stdin\n"); } break; default: fprintf(stderr, "# ERROR: Unknown character '%c'\n", *line); return 1; } line = strtok_r(NULL, "\n", &saveptr); } return 0;}
/* Returns 1 on error, 0 otherwise. */static int interpret_stream(FILE *script, char *const script_name, char *const *const envp, const bool restrict_stream){ int err; char *const script_argv[] = { script_name, NULL }; char buf[128] = {}; size_t buf_size = sizeof(buf);
/* * We pass a valid argv and envp to the kernel to emulate a native * script execution. We must use the script file descriptor instead of * the script path name to avoid race conditions. */ err = sys_execveat(fileno(script), "", script_argv, envp, AT_EMPTY_PATH | AT_EXECVE_CHECK); if (err && restrict_stream) { perror("ERROR: Script execution check"); return 1; }
/* Reads script. */ buf_size = fread(buf, 1, buf_size - 1, script); return interpret_buffer(buf, buf_size);}
static void print_usage(const char *argv0){ fprintf(stderr, "usage: %s <script.inc> | -i | -c <command>\n\n", argv0); fprintf(stderr, "Example:\n"); fprintf(stderr, " ./set-exec -fi -- ./inc -i < script-exec.inc\n");}
int main(const int argc, char *const argv[], char *const *const envp){ int opt; char *cmd = NULL; char *script_name = NULL; bool interpret_stdin = false; FILE *script_file = NULL; int secbits; bool deny_interactive, restrict_file; size_t arg_nb;
secbits = prctl(PR_GET_SECUREBITS); if (secbits == -1) { /* * This should never happen, except with a buggy seccomp * filter. */ perror("ERROR: Failed to get securebits"); return 1; }
deny_interactive = !!(secbits & SECBIT_EXEC_DENY_INTERACTIVE); restrict_file = !!(secbits & SECBIT_EXEC_RESTRICT_FILE);
while ((opt = getopt(argc, argv, "c:i")) != -1) { switch (opt) { case 'c': if (cmd) { fprintf(stderr, "ERROR: Command already set"); return 1; } cmd = optarg; break; case 'i': interpret_stdin = true; break; default: print_usage(argv[0]); return 1; } }
/* Checks that only one argument is used, or read stdin. */ arg_nb = !!cmd + !!interpret_stdin; if (arg_nb == 0 && argc == 2) { script_name = argv[1]; } else if (arg_nb != 1) { print_usage(argv[0]); return 1; }
if (cmd) { /* * Other kind of interactive interpretations should be denied * as well (e.g. CLI arguments passing script snippets, * environment variables interpreted as script). However, any * way to pass script files should only be restricted according * to restrict_file. */ if (deny_interactive) { fprintf(stderr, "ERROR: Interactive interpretation denied.\n"); return 1; }
return interpret_buffer(cmd, strlen(cmd)); }
if (interpret_stdin && !script_name) { script_file = stdin; /* * As for any execve(2) call, this path may be logged by the * kernel. */ script_name = "/proc/self/fd/0"; /* * When stdin is used, it can point to a regular file or a * pipe. Restrict stdin execution according to * SECBIT_EXEC_DENY_INTERACTIVE but always allow executable * files (which are not considered as interactive inputs). */ return interpret_stream(script_file, script_name, envp, deny_interactive); } else if (script_name && !interpret_stdin) { /* * In this sample, we don't pass any argument to scripts, but * otherwise we would have to forge an argv with such * arguments. */ script_file = fopen(script_name, "r"); if (!script_file) { perror("ERROR: Failed to open script"); return 1; } /* * Restricts file execution according to * SECBIT_EXEC_RESTRICT_FILE. */ return interpret_stream(script_file, script_name, envp, restrict_file); }
print_usage(argv[0]); return 1;}