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authorEric W. Biederman <ebiederm@xmission.com>2018-10-25 09:04:18 -0500
committerEric W. Biederman <ebiederm@xmission.com>2018-11-08 00:30:30 -0600
commitdf7342b240185d58d3d9665c0bbf0a0f5570ec29 (patch)
tree2364c5f9c7f873d999f521c4a6227dfb19b786a6 /fs/namespace.c
parent25d202ed820ee347edec0bf3bf553544556bf64b (diff)
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mount: Don't allow copying MNT_UNBINDABLE|MNT_LOCKED mounts
Jonathan Calmels from NVIDIA reported that he's able to bypass the mount visibility security check in place in the Linux kernel by using a combination of the unbindable property along with the private mount propagation option to allow a unprivileged user to see a path which was purposefully hidden by the root user. Reproducer: # Hide a path to all users using a tmpfs root@castiana:~# mount -t tmpfs tmpfs /sys/devices/ root@castiana:~# # As an unprivileged user, unshare user namespace and mount namespace stgraber@castiana:~$ unshare -U -m -r # Confirm the path is still not accessible root@castiana:~# ls /sys/devices/ # Make /sys recursively unbindable and private root@castiana:~# mount --make-runbindable /sys root@castiana:~# mount --make-private /sys # Recursively bind-mount the rest of /sys over to /mnnt root@castiana:~# mount --rbind /sys/ /mnt # Access our hidden /sys/device as an unprivileged user root@castiana:~# ls /mnt/devices/ breakpoint cpu cstate_core cstate_pkg i915 intel_pt isa kprobe LNXSYSTM:00 msr pci0000:00 platform pnp0 power software system tracepoint uncore_arb uncore_cbox_0 uncore_cbox_1 uprobe virtual Solve this by teaching copy_tree to fail if a mount turns out to be both unbindable and locked. Cc: stable@vger.kernel.org Fixes: 5ff9d8a65ce8 ("vfs: Lock in place mounts from more privileged users") Reported-by: Jonathan Calmels <jcalmels@nvidia.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'fs/namespace.c')
-rw-r--r--fs/namespace.c10
1 files changed, 8 insertions, 2 deletions
diff --git a/fs/namespace.c b/fs/namespace.c
index 72f10c40fe3f..e0e0f9cf6c30 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1734,8 +1734,14 @@ struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
for (s = r; s; s = next_mnt(s, r)) {
if (!(flag & CL_COPY_UNBINDABLE) &&
IS_MNT_UNBINDABLE(s)) {
- s = skip_mnt_tree(s);
- continue;
+ if (s->mnt.mnt_flags & MNT_LOCKED) {
+ /* Both unbindable and locked. */
+ q = ERR_PTR(-EPERM);
+ goto out;
+ } else {
+ s = skip_mnt_tree(s);
+ continue;
+ }
}
if (!(flag & CL_COPY_MNT_NS_FILE) &&
is_mnt_ns_file(s->mnt.mnt_root)) {