On Thu, Apr 10, 2014 at 4:16 PM, David Herrmann <dh.herrmann@xxxxxxxxx> wrote: > Hi > > On Fri, Apr 11, 2014 at 1:05 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >> /proc/pid/fd is a really weird corner case in which the mode of an >> inode that doesn't have a name matters. I suspect that almost no one >> will ever want to open one of these things out of /proc/self/fd, and >> those who do should be made to think about it. > > I'm arguing in the context of memfd, and there's no security leak if > people get access to the underlying inode (at least I'm not aware of > any). I'm not sure what you mean. > As I said, context information is attached to the inode, not > file context, so I'm fine if people want to open multiple file > contexts via /proc. If someone wants to forbid open(), I want to hear > _why_. I assume the memfd object has uid==uid-of-creator and > mode==(777 & ~umask) (which usually results in X00, so no access for > non-owners). I cannot see how /proc is a security issue here. On further reflection, my argument for 000 is crap. As far as I can see, the only time that the mode matters at all when playing with /proc/pid/fd, and they only way to get a non-O_RDWR memfd is using /proc/pid/fd, so I'll argue for 0600 instead. Argument why 0600 is better than 0600 & ~umask: either callers don't care because the inode mode simply doesn't matter or they're using /proc/pid/fd to *reduce* permissions, in which case they'd probably like to avoid having to play with umask or call fchmod. Argument why 0600 is better than 0777 & ~umask: People /prod/pid/fd are the only ones who care, in which case they probably prefer for the permissions not be increased by other users if they give them a reduced-permission fd. Anyway, this is all mostly unimportant. Some text in the man page is probably sufficient, but I still think that 0600 is trivial to implement and a little bit more friendly. --Andy > > Thanks > David -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>