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fs: Allow listmount() in foreign mount namespace

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Expand struct mnt_id_req to add an optional mnt_ns_id field.  When this
field is populated, listmount() will be performed on the specified mount
namespace, provided the currently application has CAP_SYS_ADMIN in its
user namespace and the mount namespace is a child of the current
namespace.

Co-developed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/49930bdce29a8367a213eb14c1e68e7e49284f86.1719243756.git.josef@toxicpanda.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2024-06-24 11:49:48 -04:00
parent 09b31295f8
commit 0a3deb1185
No known key found for this signature in database
GPG key ID: 91C61BC06578DCA2
2 changed files with 72 additions and 18 deletions
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88
fs/namespace.c
View file

@ -5122,7 +5122,7 @@ static int copy_mnt_id_req(const struct mnt_id_req __user *req,
int ret;
size_t usize;
BUILD_BUG_ON(sizeof(struct mnt_id_req) != MNT_ID_REQ_SIZE_VER0);
BUILD_BUG_ON(sizeof(struct mnt_id_req) != MNT_ID_REQ_SIZE_VER1);
ret = get_user(usize, &req->size);
if (ret)
@ -5140,6 +5140,58 @@ static int copy_mnt_id_req(const struct mnt_id_req __user *req,
return 0;
}
static struct mount *listmnt_next(struct mount *curr, bool reverse)
{
struct rb_node *node;
if (reverse)
node = rb_prev(&curr->mnt_node);
else
node = rb_next(&curr->mnt_node);
return node_to_mount(node);
}
static int grab_requested_root(struct mnt_namespace *ns, struct path *root)
{
struct mount *first;
rwsem_assert_held(&namespace_sem);
/* We're looking at our own ns, just use get_fs_root. */
if (ns == current->nsproxy->mnt_ns) {
get_fs_root(current->fs, root);
return 0;
}
/*
* We have to find the first mount in our ns and use that, however it
* may not exist, so handle that properly.
*/
if (RB_EMPTY_ROOT(&ns->mounts))
return -ENOENT;
first = listmnt_next(ns->root, false);
if (!first)
return -ENOENT;
root->mnt = mntget(&first->mnt);
root->dentry = dget(root->mnt->mnt_root);
return 0;
}
/*
* If the user requested a specific mount namespace id, look that up and return
* that, or if not simply grab a passive reference on our mount namespace and
* return that.
*/
static struct mnt_namespace *grab_requested_mnt_ns(u64 mnt_ns_id)
{
if (mnt_ns_id)
return lookup_mnt_ns(mnt_ns_id);
refcount_inc(&current->nsproxy->mnt_ns->passive);
return current->nsproxy->mnt_ns;
}
SYSCALL_DEFINE4(statmount, const struct mnt_id_req __user *, req,
struct statmount __user *, buf, size_t, bufsize,
unsigned int, flags)
@ -5185,30 +5237,21 @@ retry:
return ret;
}
static struct mount *listmnt_next(struct mount *curr, bool reverse)
{
struct rb_node *node;
if (reverse)
node = rb_prev(&curr->mnt_node);
else
node = rb_next(&curr->mnt_node);
return node_to_mount(node);
}
static ssize_t do_listmount(u64 mnt_parent_id, u64 last_mnt_id, u64 *mnt_ids,
size_t nr_mnt_ids, bool reverse)
static ssize_t do_listmount(struct mnt_namespace *ns, u64 mnt_parent_id,
u64 last_mnt_id, u64 *mnt_ids, size_t nr_mnt_ids,
bool reverse)
{
struct path root __free(path_put) = {};
struct mnt_namespace *ns = current->nsproxy->mnt_ns;
struct path orig;
struct mount *r, *first;
ssize_t ret;
rwsem_assert_held(&namespace_sem);
get_fs_root(current->fs, &root);
ret = grab_requested_root(ns, &root);
if (ret)
return ret;
if (mnt_parent_id == LSMT_ROOT) {
orig = root;
} else {
@ -5260,6 +5303,7 @@ SYSCALL_DEFINE4(listmount, const struct mnt_id_req __user *, req,
{
u64 *kmnt_ids __free(kvfree) = NULL;
const size_t maxcount = 1000000;
struct mnt_namespace *ns __free(mnt_ns_release) = NULL;
struct mnt_id_req kreq;
ssize_t ret;
@ -5286,8 +5330,16 @@ SYSCALL_DEFINE4(listmount, const struct mnt_id_req __user *, req,
if (!kmnt_ids)
return -ENOMEM;
ns = grab_requested_mnt_ns(kreq.mnt_ns_id);
if (!ns)
return -ENOENT;
if (kreq.mnt_ns_id && (ns != current->nsproxy->mnt_ns) &&
!ns_capable_noaudit(ns->user_ns, CAP_SYS_ADMIN))
return -ENOENT;
scoped_guard(rwsem_read, &namespace_sem)
ret = do_listmount(kreq.mnt_id, kreq.param, kmnt_ids,
ret = do_listmount(ns, kreq.mnt_id, kreq.param, kmnt_ids,
nr_mnt_ids, (flags & LISTMOUNT_REVERSE));
if (copy_to_user(mnt_ids, kmnt_ids, ret * sizeof(*mnt_ids)))

2
include/uapi/linux/mount.h
View file

@ -189,10 +189,12 @@ struct mnt_id_req {
__u32 spare;
__u64 mnt_id;
__u64 param;
__u64 mnt_ns_id;
};
/* List of all mnt_id_req versions. */
#define MNT_ID_REQ_SIZE_VER0 24 /* sizeof first published struct */
#define MNT_ID_REQ_SIZE_VER1 32 /* sizeof second published struct */
/*
* @mask bits for statmount(2)