diff options
Diffstat (limited to 'src/basic/argv-util.c')
| -rw-r--r-- | src/basic/argv-util.c | 233 |
1 files changed, 233 insertions, 0 deletions
diff --git a/src/basic/argv-util.c b/src/basic/argv-util.c new file mode 100644 index 0000000..a2bcc44 --- /dev/null +++ b/src/basic/argv-util.c @@ -0,0 +1,233 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +#include <sched.h> +#include <sys/mman.h> +#include <sys/prctl.h> +#include <unistd.h> + +#include "argv-util.h" +#include "capability-util.h" +#include "errno-util.h" +#include "missing_sched.h" +#include "parse-util.h" +#include "path-util.h" +#include "process-util.h" +#include "string-util.h" +#include "strv.h" + +int saved_argc = 0; +char **saved_argv = NULL; + +bool invoked_as(char *argv[], const char *token) { + if (!argv || isempty(argv[0])) + return false; + + if (isempty(token)) + return false; + + return strstr(last_path_component(argv[0]), token); +} + +bool invoked_by_systemd(void) { + int r; + + /* If the process is directly executed by PID1 (e.g. ExecStart= or generator), systemd-importd, + * or systemd-homed, then $SYSTEMD_EXEC_PID= is set, and read the command line. */ + const char *e = getenv("SYSTEMD_EXEC_PID"); + if (!e) + return false; + + if (streq(e, "*")) + /* For testing. */ + return true; + + pid_t p; + r = parse_pid(e, &p); + if (r < 0) { + /* We know that systemd sets the variable correctly. Something else must have set it. */ + log_debug_errno(r, "Failed to parse \"SYSTEMD_EXEC_PID=%s\", ignoring: %m", e); + return false; + } + + return getpid_cached() == p; +} + +bool argv_looks_like_help(int argc, char **argv) { + char **l; + + /* Scans the command line for indications the user asks for help. This is supposed to be called by + * tools that do not implement getopt() style command line parsing because they are not primarily + * user-facing. Detects four ways of asking for help: + * + * 1. Passing zero arguments + * 2. Passing "help" as first argument + * 3. Passing --help as any argument + * 4. Passing -h as any argument + */ + + if (argc <= 1) + return true; + + if (streq_ptr(argv[1], "help")) + return true; + + l = strv_skip(argv, 1); + + return strv_contains(l, "--help") || + strv_contains(l, "-h"); +} + +static int update_argv(const char name[], size_t l) { + static int can_do = -1; + int r; + + assert(name); + assert(l < SIZE_MAX); + + if (can_do == 0) + return 0; + can_do = false; /* We'll set it to true only if the whole process works */ + + /* Calling prctl() with PR_SET_MM_ARG_{START,END} requires CAP_SYS_RESOURCE so let's use this as quick bypass + * check, to avoid calling mmap() should PR_SET_MM_ARG_{START,END} fail with EPERM later on anyway. */ + r = have_effective_cap(CAP_SYS_RESOURCE); + if (r < 0) + return log_debug_errno(r, "Failed to check if we have enough privileges: %m"); + if (r == 0) + return log_debug_errno(SYNTHETIC_ERRNO(EPERM), + "Skipping PR_SET_MM, as we don't have privileges."); + + static size_t mm_size = 0; + static char *mm = NULL; + + if (mm_size < l+1) { + size_t nn_size; + char *nn; + + nn_size = PAGE_ALIGN(l+1); + if (nn_size >= SIZE_MAX) + return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), "The requested argument is too long."); + + nn = mmap(NULL, nn_size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); + if (nn == MAP_FAILED) + return log_debug_errno(errno, "mmap() failed: %m"); + + strncpy(nn, name, nn_size); + + /* Now, let's tell the kernel about this new memory */ + if (prctl(PR_SET_MM, PR_SET_MM_ARG_START, (unsigned long) nn, 0, 0) < 0) { + if (ERRNO_IS_PRIVILEGE(errno)) + return log_debug_errno(errno, "PR_SET_MM_ARG_START failed: %m"); + + /* HACK: prctl() API is kind of dumb on this point. The existing end address may already be + * below the desired start address, in which case the kernel may have kicked this back due + * to a range-check failure (see linux/kernel/sys.c:validate_prctl_map() to see this in + * action). The proper solution would be to have a prctl() API that could set both start+end + * simultaneously, or at least let us query the existing address to anticipate this condition + * and respond accordingly. For now, we can only guess at the cause of this failure and try + * a workaround--which will briefly expand the arg space to something potentially huge before + * resizing it to what we want. */ + log_debug_errno(errno, "PR_SET_MM_ARG_START failed, attempting PR_SET_MM_ARG_END hack: %m"); + + if (prctl(PR_SET_MM, PR_SET_MM_ARG_END, (unsigned long) nn + l + 1, 0, 0) < 0) { + r = log_debug_errno(errno, "PR_SET_MM_ARG_END hack failed, proceeding without: %m"); + (void) munmap(nn, nn_size); + return r; + } + + if (prctl(PR_SET_MM, PR_SET_MM_ARG_START, (unsigned long) nn, 0, 0) < 0) + return log_debug_errno(errno, "PR_SET_MM_ARG_START still failed, proceeding without: %m"); + } else { + /* And update the end pointer to the new end, too. If this fails, we don't really know what + * to do, it's pretty unlikely that we can rollback, hence we'll just accept the failure, + * and continue. */ + if (prctl(PR_SET_MM, PR_SET_MM_ARG_END, (unsigned long) nn + l + 1, 0, 0) < 0) + log_debug_errno(errno, "PR_SET_MM_ARG_END failed, proceeding without: %m"); + } + + if (mm) + (void) munmap(mm, mm_size); + + mm = nn; + mm_size = nn_size; + } else { + strncpy(mm, name, mm_size); + + /* Update the end pointer, continuing regardless of any failure. */ + if (prctl(PR_SET_MM, PR_SET_MM_ARG_END, (unsigned long) mm + l + 1, 0, 0) < 0) + log_debug_errno(errno, "PR_SET_MM_ARG_END failed, proceeding without: %m"); + } + + can_do = true; + return 0; +} + +int rename_process(const char name[]) { + bool truncated = false; + + /* This is a like a poor man's setproctitle(). It changes the comm field, argv[0], and also the glibc's + * internally used name of the process. For the first one a limit of 16 chars applies; to the second one in + * many cases one of 10 (i.e. length of "/sbin/init") — however if we have CAP_SYS_RESOURCES it is unbounded; + * to the third one 7 (i.e. the length of "systemd". If you pass a longer string it will likely be + * truncated. + * + * Returns 0 if a name was set but truncated, > 0 if it was set but not truncated. */ + + if (isempty(name)) + return -EINVAL; /* let's not confuse users unnecessarily with an empty name */ + + if (!is_main_thread()) + return -EPERM; /* Let's not allow setting the process name from other threads than the main one, as we + * cache things without locking, and we make assumptions that PR_SET_NAME sets the + * process name that isn't correct on any other threads */ + + size_t l = strlen(name); + + /* First step, change the comm field. The main thread's comm is identical to the process comm. This means we + * can use PR_SET_NAME, which sets the thread name for the calling thread. */ + if (prctl(PR_SET_NAME, name) < 0) + log_debug_errno(errno, "PR_SET_NAME failed: %m"); + if (l >= TASK_COMM_LEN) /* Linux userspace process names can be 15 chars at max */ + truncated = true; + + /* Second step, change glibc's ID of the process name. */ + if (program_invocation_name) { + size_t k; + + k = strlen(program_invocation_name); + strncpy(program_invocation_name, name, k); + if (l > k) + truncated = true; + + /* Also update the short name. */ + char *p = strrchr(program_invocation_name, '/'); + program_invocation_short_name = p ? p + 1 : program_invocation_name; + } + + /* Third step, completely replace the argv[] array the kernel maintains for us. This requires privileges, but + * has the advantage that the argv[] array is exactly what we want it to be, and not filled up with zeros at + * the end. This is the best option for changing /proc/self/cmdline. */ + (void) update_argv(name, l); + + /* Fourth step: in all cases we'll also update the original argv[], so that our own code gets it right too if + * it still looks here */ + if (saved_argc > 0) { + if (saved_argv[0]) { + size_t k; + + k = strlen(saved_argv[0]); + strncpy(saved_argv[0], name, k); + if (l > k) + truncated = true; + } + + for (int i = 1; i < saved_argc; i++) { + if (!saved_argv[i]) + break; + + memzero(saved_argv[i], strlen(saved_argv[i])); + } + } + + return !truncated; +} |