Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933878Ab3GWSan (ORCPT ); Tue, 23 Jul 2013 14:30:43 -0400 Received: from out03.mta.xmission.com ([166.70.13.233]:51547 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933513Ab3GWSai (ORCPT ); Tue, 23 Jul 2013 14:30:38 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Linux Containers Cc: "Serge E. Hallyn" , Andy Lutomirski , , Date: Tue, 23 Jul 2013 11:30:29 -0700 Message-ID: <877gghruwq.fsf@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-AID: U2FsdGVkX1+ierHVIHZdLC2ctJn2vMT2JuGgJFfJSB0= X-SA-Exim-Connect-IP: 98.207.154.105 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 1.5 TR_Symld_Words too many words that have symbols inside * 0.7 XMSubLong Long Subject * 0.8 BAYES_50 BODY: Bayes spam probability is 40 to 60% * [score: 0.4999] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa07 1397; Body=1 Fuz1=1 Fuz2=1] X-Spam-DCC: XMission; sa07 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: **;Linux Containers X-Spam-Relay-Country: Subject: [REVIEW][PATCH] vfs: Lock in place mounts from more privileged users X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Wed, 14 Nov 2012 14:26:46 -0700) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5022 Lines: 151 When creating a less privileged mount namespace or propogating mounts from a more privileged to a less privileged mount namespace lock the submounts so they may not be unmounted individually in the child mount namespace revealing what is under them. This enforces the reasonable expectation that it is not possible to see under a mount point. Most of the time mounts are on empty directories and revealing that does not matter, however I have seen an occassionaly sloppy configuration where there were interesting things concealed under a mount point that probably should not be revealed. Expirable submounts are not locked because they will eventually unmount automatically so whatever is under them already needs to be safe for unprivileged users to access. >From a practical standpoint these restrictions do not appear to be significant for unprivileged users of the mount namespace. Recursive bind mounts and pivot_root continues to work, and mounts that are created in a mount namespace may be unmounted there. All of which means that the common idiom of keeping a directory of interesting files and using pivot_root to throw everything else away continues to work just fine. Signed-off-by: "Eric W. Biederman" --- fs/namespace.c | 34 ++++++++++++++++++++++++++++++++++ include/linux/mount.h | 1 + 2 files changed, 35 insertions(+), 0 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index 7b1ca9b..7e16a73 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -831,6 +831,10 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root, if ((flag & CL_UNPRIVILEGED) && (mnt->mnt.mnt_flags & MNT_READONLY)) mnt->mnt.mnt_flags |= MNT_LOCK_READONLY; + /* Don't allow unprivileged users to reveal what is under a mount */ + if ((flag & CL_UNPRIVILEGED) && list_empty(&old->mnt_expire)) + mnt->mnt.mnt_flags |= MNT_LOCKED; + atomic_inc(&sb->s_active); mnt->mnt.mnt_sb = sb; mnt->mnt.mnt_root = dget(root); @@ -1327,6 +1331,8 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags) goto dput_and_out; if (!check_mnt(mnt)) goto dput_and_out; + if (mnt->mnt.mnt_flags & MNT_LOCKED) + goto dput_and_out; retval = do_umount(mnt, flags); dput_and_out: @@ -1381,6 +1387,7 @@ struct mount *copy_tree(struct mount *mnt, struct dentry *dentry, if (IS_ERR(q)) return q; + q->mnt.mnt_flags &= ~MNT_LOCKED; q->mnt_mountpoint = mnt->mnt_mountpoint; p = mnt; @@ -1696,6 +1703,19 @@ static int do_change_type(struct path *path, int flag) return err; } +static bool has_locked_children(struct mount *mnt, struct dentry *dentry) +{ + struct mount *child; + list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) { + if (!is_subdir(child->mnt_mountpoint, dentry)) + continue; + + if (child->mnt.mnt_flags & MNT_LOCKED) + return true; + } + return false; +} + /* * do loopback mount. */ @@ -1731,6 +1751,9 @@ static int do_loopback(struct path *path, const char *old_name, if (!check_mnt(parent) || !check_mnt(old)) goto out2; + if (!recurse && has_locked_children(old, old_path.dentry)) + goto out2; + if (recurse) mnt = copy_tree(old, old_path.dentry, 0); else @@ -1741,6 +1764,8 @@ static int do_loopback(struct path *path, const char *old_name, goto out2; } + mnt->mnt.mnt_flags &= ~MNT_LOCKED; + err = graft_tree(mnt, parent, mp); if (err) { br_write_lock(&vfsmount_lock); @@ -1853,6 +1878,9 @@ static int do_move_mount(struct path *path, const char *old_name) if (!check_mnt(p) || !check_mnt(old)) goto out1; + if (old->mnt.mnt_flags & MNT_LOCKED) + goto out1; + err = -EINVAL; if (old_path.dentry != old_path.mnt->mnt_root) goto out1; @@ -2630,6 +2658,8 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root, goto out4; if (!check_mnt(root_mnt) || !check_mnt(new_mnt)) goto out4; + if (new_mnt->mnt.mnt_flags & MNT_LOCKED) + goto out4; error = -ENOENT; if (d_unlinked(new.dentry)) goto out4; @@ -2653,6 +2683,10 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root, br_write_lock(&vfsmount_lock); detach_mnt(new_mnt, &parent_path); detach_mnt(root_mnt, &root_parent); + if (root_mnt->mnt.mnt_flags & MNT_LOCKED) { + new_mnt->mnt.mnt_flags |= MNT_LOCKED; + root_mnt->mnt.mnt_flags &= ~MNT_LOCKED; + } /* mount old root on put_old */ attach_mnt(root_mnt, old_mnt, old_mp); /* mount new_root on / */ diff --git a/include/linux/mount.h b/include/linux/mount.h index 73005f9..38cd98f 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -48,6 +48,7 @@ struct mnt_namespace; #define MNT_INTERNAL 0x4000 #define MNT_LOCK_READONLY 0x400000 +#define MNT_LOCKED 0x800000 struct vfsmount { struct dentry *mnt_root; /* root of the mounted tree */ -- 1.7.5.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/