On Mon, Jul 06, 2020 at 03:07:13PM +0200, Christian Brauner wrote:

On Wed, Jun 17, 2020 at 03:03:24PM -0700, Kees Cook wrote:

quoted

The sock counting (sock_update_netprioidx() and sock_update_classid()) was
missing from pidfd's implementation of received fd installation. Replace
the open-coded version with a call to the new fd_install_received()
helper.

Fixes: 8649c322f75c ("pid: Implement pidfd_getfd syscall")
Signed-off-by: Kees Cook <redacted>
---
 kernel/pid.c | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/kernel/pid.c b/kernel/pid.c
index f1496b757162..24924ec5df0e 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c

@@ -635,18 +635,9 @@ static int pidfd_getfd(struct pid *pid, int fd)
 	if (IS_ERR(file))
 		return PTR_ERR(file);
 
-	ret = security_file_receive(file);
-	if (ret) {
-		fput(file);
-		return ret;
-	}
-
-	ret = get_unused_fd_flags(O_CLOEXEC);
+	ret = fd_install_received(file, O_CLOEXEC);
 	if (ret < 0)
 		fput(file);
-	else
-		fd_install(ret, file);

So someone just sent a fix for pidfd_getfd() that was based on the
changes done here.

Hi! Ah yes, that didn't get CCed to me. I'll go reply.

I've been on vacation so didn't have a change to review this series and
I see it's already in linux-next. This introduces a memory leak and
actually proves a point I tried to stress when adding this helper:
fd_install_received() in contrast to fd_install() does _not_ consume a
reference because it takes one before it calls into fd_install(). That
means, you need an unconditional fput() here both in the failure and
error path.

Yup, this was a mistake in my refactoring of the pidfs changes.

I strongly suggest though that we simply align the behavior between
fd_install() and fd_install_received() and have the latter simply
consume a reference when it succeeds! Imho, this bug proves that I was
right to insist on this before. ;)

I still don't agree: it radically complicates the SCM_RIGHTS and seccomp
cases. The primary difference is that fd_install() cannot fail, and it
was optimized for this situation. The other file-related helpers that
can fail do not consume the reference, so this is in keeping with those
as well.

-- 
Kees Cook