5.4-stable review patch. If anyone has any objections, please let me know.
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From: Al Viro viro@zeniv.linux.org.uk
[ Upstream commit cffd0441872e7f6b1fce5e78fb1c99187a291330 ]
do_change_type() and do_set_group() are operating on different aspects of the same thing - propagation graph. The latter asks for mounts involved to be mounted in namespace(s) the caller has CAP_SYS_ADMIN for. The former is a mess - originally it didn't even check that mount *is* mounted. That got fixed, but the resulting check turns out to be too strict for userland - in effect, we check that mount is in our namespace, having already checked that we have CAP_SYS_ADMIN there.
What we really need (in both cases) is * only touch mounts that are mounted. That's a must-have constraint - data corruption happens if it get violated. * don't allow to mess with a namespace unless you already have enough permissions to do so (i.e. CAP_SYS_ADMIN in its userns).
That's an equivalent of what do_set_group() does; let's extract that into a helper (may_change_propagation()) and use it in both do_set_group() and do_change_type().
Fixes: 12f147ddd6de "do_change_type(): refuse to operate on unmounted/not ours mounts" Acked-by: Andrei Vagin avagin@gmail.com Reviewed-by: Pavel Tikhomirov ptikhomirov@virtuozzo.com Tested-by: Pavel Tikhomirov ptikhomirov@virtuozzo.com Reviewed-by: Christian Brauner brauner@kernel.org Signed-off-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Sasha Levin sashal@kernel.org --- fs/namespace.c | 34 ++++++++++++++++++++-------------- 1 file changed, 20 insertions(+), 14 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c index 3c1afe60d438..c87f847c959d 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2210,6 +2210,19 @@ static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp) return attach_recursive_mnt(mnt, p, mp, false); }
+static int may_change_propagation(const struct mount *m) +{ + struct mnt_namespace *ns = m->mnt_ns; + + // it must be mounted in some namespace + if (IS_ERR_OR_NULL(ns)) // is_mounted() + return -EINVAL; + // and the caller must be admin in userns of that namespace + if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) + return -EPERM; + return 0; +} + /* * Sanity check the flags to change_mnt_propagation. */ @@ -2246,10 +2259,10 @@ static int do_change_type(struct path *path, int ms_flags) return -EINVAL;
namespace_lock(); - if (!check_mnt(mnt)) { - err = -EINVAL; + err = may_change_propagation(mnt); + if (err) goto out_unlock; - } + if (type == MS_SHARED) { err = invent_group_ids(mnt, recurse); if (err) @@ -2634,18 +2647,11 @@ static int do_set_group(struct path *from_path, struct path *to_path)
namespace_lock();
- err = -EINVAL; - /* To and From must be mounted */ - if (!is_mounted(&from->mnt)) - goto out; - if (!is_mounted(&to->mnt)) - goto out; - - err = -EPERM; - /* We should be allowed to modify mount namespaces of both mounts */ - if (!ns_capable(from->mnt_ns->user_ns, CAP_SYS_ADMIN)) + err = may_change_propagation(from); + if (err) goto out; - if (!ns_capable(to->mnt_ns->user_ns, CAP_SYS_ADMIN)) + err = may_change_propagation(to); + if (err) goto out;
err = -EINVAL;