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-rw-r--r--src/basic/fd-util.c115
-rw-r--r--src/basic/fd-util.h2
-rw-r--r--src/test/test-fd-util.c69
3 files changed, 186 insertions, 0 deletions
diff --git a/src/basic/fd-util.c b/src/basic/fd-util.c
index 61a93fcb4a7..fdf69476587 100644
--- a/src/basic/fd-util.c
+++ b/src/basic/fd-util.c
@@ -615,3 +615,118 @@ int fd_move_above_stdio(int fd) {
(void) close(fd);
return copy;
}
+
+int rearrange_stdio(int original_input_fd, int original_output_fd, int original_error_fd) {
+
+ int fd[3] = { /* Put together an array of fds we work on */
+ original_input_fd,
+ original_output_fd,
+ original_error_fd
+ };
+
+ int r, i,
+ null_fd = -1, /* if we open /dev/null, we store the fd to it here */
+ copy_fd[3] = { -1, -1, -1 }; /* This contains all fds we duplicate here temporarily, and hence need to close at the end */
+ bool null_readable, null_writable;
+
+ /* Sets up stdin, stdout, stderr with the three file descriptors passed in. If any of the descriptors is
+ * specified as -1 it will be connected with /dev/null instead. If any of the file descriptors is passed as
+ * itself (e.g. stdin as STDIN_FILENO) it is left unmodified, but the O_CLOEXEC bit is turned off should it be
+ * on.
+ *
+ * Note that if any of the passed file descriptors are > 2 they will be closed — both on success and on
+ * failure! Thus, callers should assume that when this function returns the input fds are invalidated.
+ *
+ * Note that when this function fails stdin/stdout/stderr might remain half set up!
+ *
+ * O_CLOEXEC is turned off for all three file descriptors (which is how it should be for
+ * stdin/stdout/stderr). */
+
+ null_readable = original_input_fd < 0;
+ null_writable = original_output_fd < 0 || original_error_fd < 0;
+
+ /* First step, open /dev/null once, if we need it */
+ if (null_readable || null_writable) {
+
+ /* Let's open this with O_CLOEXEC first, and convert it to non-O_CLOEXEC when we move the fd to the final position. */
+ null_fd = open("/dev/null", (null_readable && null_writable ? O_RDWR :
+ null_readable ? O_RDONLY : O_WRONLY) | O_CLOEXEC);
+ if (null_fd < 0) {
+ r = -errno;
+ goto finish;
+ }
+
+ /* If this fd is in the 0…2 range, let's move it out of it */
+ if (null_fd < 3) {
+ int copy;
+
+ copy = fcntl(null_fd, F_DUPFD_CLOEXEC, 3); /* Duplicate this with O_CLOEXEC set */
+ if (copy < 0) {
+ r = -errno;
+ goto finish;
+ }
+
+ safe_close(null_fd);
+ null_fd = copy;
+ }
+ }
+
+ /* Let's assemble fd[] with the fds to install in place of stdin/stdout/stderr */
+ for (i = 0; i < 3; i++) {
+
+ if (fd[i] < 0)
+ fd[i] = null_fd; /* A negative parameter means: connect this one to /dev/null */
+ else if (fd[i] != i && fd[i] < 3) {
+ /* This fd is in the 0…2 territory, but not at its intended place, move it out of there, so that we can work there. */
+ copy_fd[i] = fcntl(fd[i], F_DUPFD_CLOEXEC, 3); /* Duplicate this with O_CLOEXEC set */
+ if (copy_fd[i] < 0) {
+ r = -errno;
+ goto finish;
+ }
+
+ fd[i] = copy_fd[i];
+ }
+ }
+
+ /* At this point we now have the fds to use in fd[], and they are all above the stdio range, so that we
+ * have freedom to move them around. If the fds already were at the right places then the specific fds are
+ * -1. Let's now move them to the right places. This is the point of no return. */
+ for (i = 0; i < 3; i++) {
+
+ if (fd[i] == i) {
+
+ /* fd is already in place, but let's make sure O_CLOEXEC is off */
+ r = fd_cloexec(i, false);
+ if (r < 0)
+ goto finish;
+
+ } else {
+ assert(fd[i] > 2);
+
+ if (dup2(fd[i], i) < 0) { /* Turns off O_CLOEXEC on the new fd. */
+ r = -errno;
+ goto finish;
+ }
+ }
+ }
+
+ r = 0;
+
+finish:
+ /* Close the original fds, but only if they were outside of the stdio range. Also, properly check for the same
+ * fd passed in multiple times. */
+ safe_close_above_stdio(original_input_fd);
+ if (original_output_fd != original_input_fd)
+ safe_close_above_stdio(original_output_fd);
+ if (original_error_fd != original_input_fd && original_error_fd != original_output_fd)
+ safe_close_above_stdio(original_error_fd);
+
+ /* Close the copies we moved > 2 */
+ for (i = 0; i < 3; i++)
+ safe_close(copy_fd[i]);
+
+ /* Close our null fd, if it's > 2 */
+ safe_close_above_stdio(null_fd);
+
+ return r;
+}
diff --git a/src/basic/fd-util.h b/src/basic/fd-util.h
index 4e8d9bc40a1..b687f1a5559 100644
--- a/src/basic/fd-util.h
+++ b/src/basic/fd-util.h
@@ -100,3 +100,5 @@ int acquire_data_fd(const void *data, size_t size, unsigned flags);
IN_SET(r, ENOTCONN, ECONNRESET, ECONNREFUSED, ECONNABORTED, EPIPE, ENETUNREACH)
int fd_move_above_stdio(int fd);
+
+int rearrange_stdio(int original_input_fd, int original_output_fd, int original_error_fd);
diff --git a/src/test/test-fd-util.c b/src/test/test-fd-util.c
index db4a7f8fda0..3f94df2eee3 100644
--- a/src/test/test-fd-util.c
+++ b/src/test/test-fd-util.c
@@ -25,6 +25,8 @@
#include "fd-util.h"
#include "fileio.h"
#include "macro.h"
+#include "path-util.h"
+#include "process-util.h"
#include "random-util.h"
#include "string-util.h"
#include "util.h"
@@ -173,6 +175,72 @@ static void test_fd_move_above_stdio(void) {
assert_se(close_nointr(new_fd) != EBADF);
}
+static void test_rearrange_stdio(void) {
+ pid_t pid;
+ int r;
+
+ r = safe_fork("rearrange", FORK_WAIT|FORK_LOG, &pid);
+ assert_se(r >= 0);
+
+ if (r == 0) {
+ _cleanup_free_ char *path = NULL;
+ char buffer[10];
+
+ /* Child */
+
+ safe_close(STDERR_FILENO); /* Let's close an fd < 2, to make it more interesting */
+
+ assert_se(rearrange_stdio(-1, -1, -1) >= 0);
+
+ assert_se(fd_get_path(STDIN_FILENO, &path) >= 0);
+ assert_se(path_equal(path, "/dev/null"));
+ path = mfree(path);
+
+ assert_se(fd_get_path(STDOUT_FILENO, &path) >= 0);
+ assert_se(path_equal(path, "/dev/null"));
+ path = mfree(path);
+
+ assert_se(fd_get_path(STDOUT_FILENO, &path) >= 0);
+ assert_se(path_equal(path, "/dev/null"));
+ path = mfree(path);
+
+ safe_close(STDIN_FILENO);
+ safe_close(STDOUT_FILENO);
+ safe_close(STDERR_FILENO);
+
+ {
+ int pair[2];
+ assert_se(pipe(pair) >= 0);
+ assert_se(pair[0] == 0);
+ assert_se(pair[1] == 1);
+ assert_se(fd_move_above_stdio(0) == 3);
+ }
+ assert_se(open("/dev/full", O_WRONLY|O_CLOEXEC) == 0);
+ assert_se(acquire_data_fd("foobar", 6, 0) == 2);
+
+ assert_se(rearrange_stdio(2, 0, 1) >= 0);
+
+ assert_se(write(1, "x", 1) < 0 && errno == ENOSPC);
+ assert_se(write(2, "z", 1) == 1);
+ assert_se(read(3, buffer, sizeof(buffer)) == 1);
+ assert_se(buffer[0] == 'z');
+ assert_se(read(0, buffer, sizeof(buffer)) == 6);
+ assert_se(memcmp(buffer, "foobar", 6) == 0);
+
+ assert_se(rearrange_stdio(-1, 1, 2) >= 0);
+ assert_se(write(1, "a", 1) < 0 && errno == ENOSPC);
+ assert_se(write(2, "y", 1) == 1);
+ assert_se(read(3, buffer, sizeof(buffer)) == 1);
+ assert_se(buffer[0] == 'y');
+
+ assert_se(fd_get_path(0, &path) >= 0);
+ assert_se(path_equal(path, "/dev/null"));
+ path = mfree(path);
+
+ _exit(EXIT_SUCCESS);
+ }
+}
+
int main(int argc, char *argv[]) {
test_close_many();
test_close_nointr();
@@ -180,6 +248,7 @@ int main(int argc, char *argv[]) {
test_open_serialization_fd();
test_acquire_data_fd();
test_fd_move_above_stdio();
+ test_rearrange_stdio();
return 0;
}
Copyright © 1996 – 2023 Jason A. Donenfeld. All Rights Reverse Engineered.