Re: [PATCH 24/32] vfs: syscall: Add fsopen() to prepare for superblock creation [ver #9]

On Wed, Jul 11, 2018 at 08:22:41AM +0100, David Howells wrote:

Andy Lutomirski [off-list ref] wrote:

quoted

quoted

   sfd = fsopen("ext4", FSOPEN_CLOEXEC);
   write(sfd, "s /dev/sdb1"); // note I'm ignoring write's length arg

Imagine some malicious program passes sfd as stdout to a setuid
program. That program gets persuaded to write "s /etc/shadow".  What
happens?  You’re okay as long as *every single fs* gets it right, but that’s
asking a lot.

Do note that you must already have CAP_SYS_ADMIN to be able to call fsopen().

David

Not really, by default an unprivileged user can still do:

	unshare(CLONE_NEWUSER|CLONE_NEWNS);
	syscall(__NR_fsopen, "ext4", 0);

- Eric