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Date: Sun, 22 Apr 2007 08:47:31 +0200 From: Miklos Szeredi <miklos@...redi.hu> To: ebiederm@...ssion.com CC: akpm@...ux-foundation.org, miklos@...redi.hu, serue@...ibm.com, viro@....linux.org.uk, linuxram@...ibm.com, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, containers@...ts.osdl.org Subject: Re: [patch 2/8] allow unprivileged umount > > On Sat, 21 Apr 2007 10:09:42 +0200 Miklos Szeredi <miklos@...redi.hu> wrote: > > > >> > > +static bool permit_umount(struct vfsmount *mnt, int flags) > >> > > +{ > >> > > > >> > > ... > >> > > > >> > > + return mnt->mnt_uid == current->uid; > >> > > +} > >> > > >> > Yes, this seems very wrong. I'd have thought that comparing user_struct*'s > >> > would get us a heck of a lot closer to being able to support aliasing of > >> > UIDs between different namespaces. > >> > > >> > >> OK, I'll fix this up. > >> > >> Actually an earlier version of this patch did use user_struct's but > >> I'd changed it to uids, because it's simpler. > > > > OK.. > > > >> I didn't think about > >> this being contrary to the id namespaces thing. > > > > Well I was madly assuming that when serarate UID namespaces are in use, UID > > 42 in container A will have a different user_struct from UID 42 in > > container B. I'd suggest that we provoke an opinion from Eric & co before > > you do work on this. > > That is what I what I have been thinking as well, Does this mean, that containers will need this? Or that you don't know yet? > storing a user struct on each mount point seems sane, plus it allows > per user mount rlimits which is major plus. Especially since we > seem to be doing accounting only for user mounts a per user rlimit > seems good. I'm not against per-user rlimits for mounts, but I'd rather do this later... > To get the user we should be user fs_uid as HPA suggested. fsuid is exclusively used for checking file permissions, which we don't do here anymore. So while it could be argued, that mount() _is_ a filesystem operation, it is really a different sort of filesystem operation than the rest. OTOH it wouldn't hurt to use fsuid instead of ruid... > Finally I'm pretty certain the capability we should care about in > this context is CAP_SETUID. Instead of CAP_SYS_ADMIN. > > If we have CAP_SETUID we can become which ever user owns the mount, > and the root user in a container needs this, so he can run login > programs. So changing the appropriate super user checks from > CAP_SYS_ADMIN to CAP_SETUID I think is the right thing todo. That's a flawed logic. If you want to mount as a specific user, and you have CAP_SETUID, then just use set*uid() and then mount(). Changing the capability check for mount() would break the userspace ABI. Miklos - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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