Merge pull request #20288 from keszybz/freeze-no-malloc

Don't call malloc from freeze which is called in a signal handler

src/shared/exec-util.c

@@ -448,6 +448,29 @@ ExecCommandFlags exec_command_flags_from_string(const char *s) {
                 return 1 << idx;
 }
 
+_noreturn_ void freeze(void) {
+        log_close();
+
+        /* Make sure nobody waits for us on a socket anymore */
+        (void) close_all_fds_full(NULL, 0, false);
+
+        sync();
+
+        /* Let's not freeze right away, but keep reaping zombies. */
+        for (;;) {
+                int r;
+                siginfo_t si = {};
+
+                r = waitid(P_ALL, 0, &si, WEXITED);
+                if (r < 0 && errno != EINTR)
+                        break;
+        }
+
+        /* waitid() failed with an unexpected error, things are really borked. Freeze now! */
+        for (;;)
+                pause();
+}
+
 int fexecve_or_execve(int executable_fd, const char *executable, char *const argv[], char *const envp[]) {
 #if ENABLE_FEXECVE
         execveat(executable_fd, "", argv, envp, AT_EMPTY_PATH);
@@ -470,3 +493,76 @@ int fexecve_or_execve(int executable_fd, const char *executable, char *const arg
                 execve(executable, argv, envp);
         return -errno;
 }
+
+int fork_agent(const char *name, int except[], size_t n_except, pid_t *ret_pid, const char *path, ...) {
+        bool stdout_is_tty, stderr_is_tty;
+        size_t n, i;
+        va_list ap;
+        char **l;
+        int r;
+
+        assert(path);
+
+        /* Spawns a temporary TTY agent, making sure it goes away when we go away */
+
+        r = safe_fork_full(name,
+                           except,
+                           n_except,
+                           FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_CLOSE_ALL_FDS|FORK_REOPEN_LOG,
+                           ret_pid);
+        if (r < 0)
+                return r;
+        if (r > 0)
+                return 0;
+
+        /* In the child: */
+
+        stdout_is_tty = isatty(STDOUT_FILENO);
+        stderr_is_tty = isatty(STDERR_FILENO);
+
+        if (!stdout_is_tty || !stderr_is_tty) {
+                int fd;
+
+                /* Detach from stdout/stderr and reopen /dev/tty for them. This is important to ensure that
+                 * when systemctl is started via popen() or a similar call that expects to read EOF we
+                 * actually do generate EOF and not delay this indefinitely by keeping an unused copy of
+                 * stdin around. */
+                fd = open("/dev/tty", O_WRONLY);
+                if (fd < 0) {
+                        log_error_errno(errno, "Failed to open /dev/tty: %m");
+                        _exit(EXIT_FAILURE);
+                }
+
+                if (!stdout_is_tty && dup2(fd, STDOUT_FILENO) < 0) {
+                        log_error_errno(errno, "Failed to dup2 /dev/tty: %m");
+                        _exit(EXIT_FAILURE);
+                }
+
+                if (!stderr_is_tty && dup2(fd, STDERR_FILENO) < 0) {
+                        log_error_errno(errno, "Failed to dup2 /dev/tty: %m");
+                        _exit(EXIT_FAILURE);
+                }
+
+                safe_close_above_stdio(fd);
+        }
+
+        (void) rlimit_nofile_safe();
+
+        /* Count arguments */
+        va_start(ap, path);
+        for (n = 0; va_arg(ap, char*); n++)
+                ;
+        va_end(ap);
+
+        /* Allocate strv */
+        l = newa(char*, n + 1);
+
+        /* Fill in arguments */
+        va_start(ap, path);
+        for (i = 0; i <= n; i++)
+                l[i] = va_arg(ap, char*);
+        va_end(ap);
+
+        execv(path, l);
+        _exit(EXIT_FAILURE);
+}

src/shared/exec-util.h

@@ -47,4 +47,8 @@ extern const gather_stdout_callback_t gather_environment[_STDOUT_CONSUME_MAX];
 const char* exec_command_flags_to_string(ExecCommandFlags i);
 ExecCommandFlags exec_command_flags_from_string(const char *s);
 
+_noreturn_ void freeze(void);
+
 int fexecve_or_execve(int executable_fd, const char *executable, char *const argv[], char *const envp[]);
+
+int fork_agent(const char *name, int except[], size_t n_except, pid_t *ret_pid, const char *path, ...) _sentinel_;

src/shared/mount-util.c

@@ -11,6 +11,7 @@
 
 #include "alloc-util.h"
 #include "dissect-image.h"
+#include "exec-util.h"
 #include "extract-word.h"
 #include "fd-util.h"
 #include "fileio.h"
@@ -1010,11 +1011,9 @@ static int make_userns(uid_t uid_shift, uid_t uid_range) {
         r = safe_fork("(sd-mkuserns)", FORK_CLOSE_ALL_FDS|FORK_DEATHSIG|FORK_NEW_USERNS, &pid);
         if (r < 0)
                 return r;
-        if (r == 0) {
+        if (r == 0)
                 /* Child. We do nothing here, just freeze until somebody kills us. */
                 freeze();
-                _exit(EXIT_FAILURE);
-        }
 
         xsprintf(line, UID_FMT " " UID_FMT " " UID_FMT "\n", 0, uid_shift, uid_range);
 

src/shared/spawn-ask-password-agent.c

@@ -4,6 +4,7 @@
 #include <stdlib.h>
 #include <unistd.h>
 
+#include "exec-util.h"
 #include "log.h"
 #include "process-util.h"
 #include "spawn-ask-password-agent.h"

src/shared/spawn-polkit-agent.c

@@ -6,6 +6,7 @@
 #include <stdlib.h>
 #include <unistd.h>
 
+#include "exec-util.h"
 #include "fd-util.h"
 #include "io-util.h"
 #include "log.h"