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);
}