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| author | Christian Brauner <brauner@kernel.org> | 2025-01-28 11:33:43 +0100 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2025-02-12 12:12:28 +0100 |
| commit | 2462651ffa76b87f9c2e4403ef6e6b89b703fb2f (patch) | |
| tree | f25a6e75dd2f1b58452ffb8830b7828ce641f2cb /fs/namespace.c | |
| parent | 325cca846fe4ed20fa68c076e25878ea9d350515 (diff) | |
| download | random-2462651ffa76b87f9c2e4403ef6e6b89b703fb2f.tar.gz | |
fs: allow changing idmappings
This patchset makes it possible to create a new idmapped mount from an
already idmapped mount and to clear idmappings.
// Create a first idmapped mount
struct mount_attr attr = {
.attr_set = MOUNT_ATTR_IDMAP
.userns_fd = fd_userns
};
fd_tree = open_tree(-EBADF, "/", OPEN_TREE_CLONE, &attr, sizeof(attr));
move_mount(fd_tree, "", -EBADF, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
// Create a second idmapped mount from the first idmapped mount
attr.attr_set = MOUNT_ATTR_IDMAP;
attr.userns_fd = fd_userns2;
fd_tree2 = open_tree(-EBADF, "/mnt", OPEN_TREE_CLONE, &attr, sizeof(attr));
// Create a second non-idmapped mount from the first idmapped mount:
memset(&attr, 0, sizeof(attr));
attr.attr_clr = MOUNT_ATTR_IDMAP;
fd_tree2 = open_tree(-EBADF, "/mnt", OPEN_TREE_CLONE, &attr, sizeof(attr));
Link: https://lore.kernel.org/r/20250128-work-mnt_idmap-update-v2-v1-5-c25feb0d2eb3@kernel.org
Reviewed-by: "Seth Forshee (DigitalOcean)" <sforshee@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'fs/namespace.c')
| -rw-r--r-- | fs/namespace.c | 53 |
1 files changed, 32 insertions, 21 deletions
diff --git a/fs/namespace.c b/fs/namespace.c index a6d3f2041fda88..1d8d14ca6c13dd 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -89,6 +89,7 @@ static LIST_HEAD(mnt_ns_list); /* protected by mnt_ns_tree_lock */ enum mount_kattr_flags_t { MOUNT_KATTR_RECURSE = (1 << 0), + MOUNT_KATTR_IDMAP_REPLACE = (1 << 1), }; struct mount_kattr { @@ -4612,11 +4613,10 @@ static int can_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt) return -EINVAL; /* - * Once a mount has been idmapped we don't allow it to change its - * mapping. It makes things simpler and callers can just create - * another bind-mount they can idmap if they want to. + * We only allow an mount to change it's idmapping if it has + * never been accessible to userspace. */ - if (is_idmapped_mnt(m)) + if (!(kattr->kflags & MOUNT_KATTR_IDMAP_REPLACE) && is_idmapped_mnt(m)) return -EPERM; /* The underlying filesystem doesn't support idmapped mounts yet. */ @@ -4706,18 +4706,16 @@ static int mount_setattr_prepare(struct mount_kattr *kattr, struct mount *mnt) static void do_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt) { + struct mnt_idmap *old_idmap; + if (!kattr->mnt_idmap) return; - /* - * Pairs with smp_load_acquire() in mnt_idmap(). - * - * Since we only allow a mount to change the idmapping once and - * verified this in can_idmap_mount() we know that the mount has - * @nop_mnt_idmap attached to it. So there's no need to drop any - * references. - */ + old_idmap = mnt_idmap(&mnt->mnt); + + /* Pairs with smp_load_acquire() in mnt_idmap(). */ smp_store_release(&mnt->mnt.mnt_idmap, mnt_idmap_get(kattr->mnt_idmap)); + mnt_idmap_put(old_idmap); } static void mount_setattr_commit(struct mount_kattr *kattr, struct mount *mnt) @@ -4826,13 +4824,23 @@ static int build_mount_idmapped(const struct mount_attr *attr, size_t usize, if (!((attr->attr_set | attr->attr_clr) & MOUNT_ATTR_IDMAP)) return 0; - /* - * We currently do not support clearing an idmapped mount. If this ever - * is a use-case we can revisit this but for now let's keep it simple - * and not allow it. - */ - if (attr->attr_clr & MOUNT_ATTR_IDMAP) - return -EINVAL; + if (attr->attr_clr & MOUNT_ATTR_IDMAP) { + /* + * We can only remove an idmapping if it's never been + * exposed to userspace. + */ + if (!(kattr->kflags & MOUNT_KATTR_IDMAP_REPLACE)) + return -EINVAL; + + /* + * Removal of idmappings is equivalent to setting + * nop_mnt_idmap. + */ + if (!(attr->attr_set & MOUNT_ATTR_IDMAP)) { + kattr->mnt_idmap = &nop_mnt_idmap; + return 0; + } + } if (attr->userns_fd > INT_MAX) return -EINVAL; @@ -4923,8 +4931,10 @@ static int build_mount_kattr(const struct mount_attr *attr, size_t usize, static void finish_mount_kattr(struct mount_kattr *kattr) { - put_user_ns(kattr->mnt_userns); - kattr->mnt_userns = NULL; + if (kattr->mnt_userns) { + put_user_ns(kattr->mnt_userns); + kattr->mnt_userns = NULL; + } if (kattr->mnt_idmap) mnt_idmap_put(kattr->mnt_idmap); @@ -5019,6 +5029,7 @@ SYSCALL_DEFINE5(open_tree_attr, int, dfd, const char __user *, filename, int ret; struct mount_kattr kattr = {}; + kattr.kflags = MOUNT_KATTR_IDMAP_REPLACE; if (flags & AT_RECURSIVE) kattr.kflags |= MOUNT_KATTR_RECURSE; |