Fix dup2 in the case where the two fds are equal.
dup3's behavior differs from dup2 in this case, so we need to paper
over that in the C library.
Change-Id: I313cd6f226db5e237f61866f324c5ecdd12bf762
diff --git a/libc/bionic/dup2.cpp b/libc/bionic/dup2.cpp
index 0b8632b..98c5646 100644
--- a/libc/bionic/dup2.cpp
+++ b/libc/bionic/dup2.cpp
@@ -26,8 +26,19 @@
* SUCH DAMAGE.
*/
+#include <fcntl.h>
#include <unistd.h>
int dup2(int old_fd, int new_fd) {
+ // If old_fd is equal to new_fd and a valid file descriptor, dup2 returns
+ // old_fd without closing it. This is not true of dup3, so we have to
+ // handle this case ourselves.
+ if (old_fd == new_fd) {
+ if (fcntl(old_fd, F_GETFD) == -1) {
+ return -1;
+ }
+ return old_fd;
+ }
+
return dup3(old_fd, new_fd, 0);
}
diff --git a/tests/unistd_test.cpp b/tests/unistd_test.cpp
index f5c0524..f54a461 100644
--- a/tests/unistd_test.cpp
+++ b/tests/unistd_test.cpp
@@ -801,3 +801,22 @@
VERIFY_SYSCONF_NOT_SUPPORT(_SC_XOPEN_UUCP);
#endif // defined(__BIONIC__)
}
+
+TEST(unistd, dup2_same) {
+ // POSIX says of dup2:
+ // If fildes2 is already a valid open file descriptor ...
+ // [and] fildes is equal to fildes2 ... dup2() shall return
+ // fildes2 without closing it.
+ // This isn't true of dup3(2), so we need to manually implement that.
+
+ // Equal and valid.
+ int fd = open("/proc/version", O_RDONLY);
+ ASSERT_TRUE(fd != -1);
+ ASSERT_EQ(fd, dup2(fd, fd));
+ ASSERT_EQ(0, close(fd)); // Check that dup2 didn't close fd.
+
+ // Equal, but invalid.
+ errno = 0;
+ ASSERT_EQ(-1, dup2(fd, fd));
+ ASSERT_EQ(EBADF, errno);
+}