#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
+#include <sched.h>
#include <lttngerr.h>
+/*
+ * We allocate a stack of twice this size and point in the middle of it
+ * to support archs with stack growing up and down.
+ */
+#define CHILD_STACK_SIZE 2048
+
+struct run_as_data {
+ int (*cmd)(void *data);
+ void *data;
+ uid_t uid;
+ gid_t gid;
+ int retval_pipe;
+};
+
struct mkdir_data {
const char *path;
mode_t mode;
return open(data->path, data->flags, data->mode);
}
+static
+int child_run_as(void *_data)
+{
+ struct run_as_data *data = _data;
+ size_t writelen, writeleft, index;
+ union {
+ int i;
+ char c[sizeof(int)];
+ } sendret;
+ int ret;
+
+ /*
+ * Child: it is safe to drop egid and euid while sharing the
+ * file descriptors with the parent process, since we do not
+ * drop "uid": therefore, the user we are dropping egid/euid to
+ * cannot attach to this process with, e.g. ptrace, nor map this
+ * process memory.
+ */
+ ret = setegid(data->gid);
+ if (ret < 0) {
+ perror("setegid");
+ exit(EXIT_FAILURE);
+ }
+ ret = seteuid(data->uid);
+ if (ret < 0) {
+ perror("seteuid");
+ exit(EXIT_FAILURE);
+ }
+ /*
+ * Also set umask to 0 for mkdir executable bit.
+ */
+ umask(0);
+ sendret.i = (*data->cmd)(data->data);
+ /* send back return value */
+ writeleft = sizeof(sendret);
+ index = 0;
+ do {
+ writelen = write(data->retval_pipe, &sendret.c[index],
+ writeleft);
+ if (writelen < 0) {
+ perror("write");
+ exit(EXIT_FAILURE);
+ }
+ writeleft -= writelen;
+ index += writelen;
+ } while (writeleft > 0);
+
+ exit(EXIT_SUCCESS);
+}
+
static
int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
{
+ struct run_as_data run_as_data;
int ret = 0;
+ int status;
pid_t pid;
+ char *child_stack;
+ int retval_pipe[2];
+ ssize_t readlen, readleft, index;
+ union {
+ int i;
+ char c[sizeof(int)];
+ } retval;
/*
* If we are non-root, we can only deal with our own uid.
return (*cmd)(data);
}
- pid = fork();
- if (pid > 0) {
- int status;
-
- /*
- * Parent: wait for child to return, in which case the
- * shared memory map will have been created.
- */
- pid = wait(&status);
- if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
- ret = -1;
- goto end;
- }
+ child_stack = malloc(CHILD_STACK_SIZE * 2);
+ if (!child_stack) {
+ return -ENOMEM;
+ }
+ ret = pipe(retval_pipe);
+ if (ret < 0) {
+ perror("pipe");
goto end;
- } else if (pid == 0) {
- /* Child */
- setegid(gid);
- if (ret < 0) {
- perror("setegid");
- exit(EXIT_FAILURE);
- }
- ret = seteuid(uid);
- if (ret < 0) {
- perror("seteuid");
- exit(EXIT_FAILURE);
+ }
+ run_as_data.data = data;
+ run_as_data.cmd = cmd;
+ run_as_data.uid = uid;
+ run_as_data.gid = gid;
+ run_as_data.retval_pipe = retval_pipe[1]; /* write end */
+
+ pid = clone(child_run_as, child_stack + CHILD_STACK_SIZE,
+ CLONE_FILES | SIGCHLD, &run_as_data, NULL);
+ if (pid < 0) {
+ perror("clone");
+ ret = pid;
+ goto close_pipe;
+ }
+ /* receive return value */
+ readleft = sizeof(retval);
+ index = 0;
+ do {
+ readlen = read(retval_pipe[0], &retval.c[index], readleft);
+ if (readlen < 0) {
+ perror("read");
+ ret = -1;
+ break;
}
- umask(0);
- ret = (*cmd)(data);
- if (!ret)
- exit(EXIT_SUCCESS);
- else
- exit(EXIT_FAILURE);
- } else {
- return -1;
+ readleft -= readlen;
+ index += readlen;
+ } while (readleft > 0);
+
+ /*
+ * Parent: wait for child to return, in which case the
+ * shared memory map will have been created.
+ */
+ pid = wait(&status);
+ if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
+ perror("wait");
+ ret = -1;
}
+close_pipe:
+ close(retval_pipe[0]);
+ close(retval_pipe[1]);
end:
- return ret;
+ free(child_stack);
+ return retval.i;
}
int mkdir_recursive_run_as(const char *path, mode_t mode, uid_t uid, gid_t gid)
*/
int open_run_as(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
{
- //struct open_data data;
- int fd, ret;
-
- DBG3("open() %s with flags %d mode %d for uid %d and gid %d",
- path, flags, mode, uid, gid);
- fd = open(path, flags, mode);
- if (fd < 0) {
- perror("open");
- return fd;
- }
- ret = fchown(fd, uid, gid);
- if (ret < 0) {
- perror("fchown");
- close(fd);
- return ret;
- }
- return fd;
-#if 0
+ struct open_data data;
+
data.path = path;
data.flags = flags;
data.mode = mode;
return run_as(_open, &data, uid, gid);
-#endif
}
projects / lttng-tools.git / blobdiff