On Wed, Jan 25, 2017 at 1:43 PM, Ben Hutchings <ben@xxxxxxxxxxxxxxx> wrote: > On Wed, 2017-01-25 at 13:06 -0800, Andy Lutomirski wrote: >> If an unprivileged program opens a setgid file for write and passes >> the fd to a privileged program and the privileged program writes to >> it, we currently fail to clear the setgid bit. Fix it by checking >> f_cred instead of current's creds whenever a struct file is >> involved. > [...] > > What if, instead, a privileged program passes the fd to an un > unprivileged program? It sounds like a bad idea to start with, but at > least currently the unprivileged program is going to clear the setgid > bit when it writes. This change would make that behaviour more > dangerous. Hmm. Although, if a privileged program does something like: (sudo -u nobody echo blah) >setuid_program presumably it wanted to make the change. > > Perhaps there should be a capability check on both the current > credentials and file credentials? (I realise that we've considered > file credential checks to be sufficient elsewhere, but those cases > involved virtual files with special semantics, where it's clearer that > a privileged process should not pass them to an unprivileged process.) > I could go either way. What I really want to do is to write a third patch that isn't for -stable that just removes the capable() check entirely. I'm reasonably confident it won't break things for a silly reason: because it's capable() and not ns_capable(), anything it would break would also be broken in an unprivileged container, and I haven't seen any reports of package managers or similar breaking for this reason. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
