Re: [PATCH] dup2: Fix return value with oldfd == newfd and invalid fd

[Linus Torvalds <torvalds@linux-foundation.org>]

On Mon, 11 May 2009, Jeff Mahoney wrote:
> 
>  The return value of dup2 when oldfd == newfd and the fd isn't valid is not
>  getting properly sign extended. We end up with 4294967287 instead of -EBADF.

Indeed.

>  This patch uses a signed int for the error value so it is properly extended.

However, I'd rather move the new variable into the block where it is used, 
and keep the whole corner-case thing self-contained.

So can you verify that this trivial variation on the patch is ok by you, 
and I'll commit it as yours with your message? (I realize it's really 
trivial, and I could just do this myself, but good to get the change 
ack'ed anyway).

		Linus

---
 fs/fcntl.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index cc8e4de..1ad7031 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -117,11 +117,13 @@ SYSCALL_DEFINE2(dup2, unsigned int, oldfd, unsigned int, newfd)
 {
 	if (unlikely(newfd == oldfd)) { /* corner case */
 		struct files_struct *files = current->files;
+		int retval = oldfd;
+
 		rcu_read_lock();
 		if (!fcheck_files(files, oldfd))
-			oldfd = -EBADF;
+			retval = -EBADF;
 		rcu_read_unlock();
-		return oldfd;
+		return retval;
 	}
 	return sys_dup3(oldfd, newfd, 0);
 }