[RFC PATCH 06/27] containers, vfs: Allow syscall dirfd arguments to take a container fd
From: David Howells <dhowells@redhat.com>
Date: 2019-02-15 16:08:24
Also in:
keyrings, linux-cifs, linux-fsdevel, linux-nfs, lkml
Subsystem:
filesystems (vfs and infrastructure), the rest · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds
Some filesystem system calls, such as mkdirat(), take a 'directory fd' to
specify the pathwalk origin. This takes either AT_FDCWD or a file
descriptor that refers to an open directory.
Make it possible to supply a container fd, as obtained from
container_create(), instead thereby specifying the container's root as the
origin. This performs the filesystem operation into the container's mount
namespace. For example:
int cfd = container_create("fred", CONTAINER_NEW_MNT_NS, 0);
mkdirat(cfd, "/fred", 0755);
A better way to do this might be to temporarily override current->fs and
current->nsproxy, but this requires splitting those fields so that procfs
doesn't see the override.
A sequence number and lock are available to protect the root pointer in
case container_chroot() and/or container_pivot_root() are implemented.
Signed-off-by: David Howells <dhowells@redhat.com>
---
fs/namei.c | 45 ++++++++++++++++++++++++++++++++++-----------
1 file changed, 34 insertions(+), 11 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index a85deb55d0c9..4932b5467285 100644
--- a/fs/namei.c
+++ b/fs/namei.c@@ -2232,20 +2232,43 @@ static const char *path_init(struct nameidata *nd, unsigned flags) if (!f.file) return ERR_PTR(-EBADF); - dentry = f.file->f_path.dentry; + if (is_container_file(f.file)) { + struct container *c = f.file->private_data; + unsigned seq; - if (*s && unlikely(!d_can_lookup(dentry))) { - fdput(f); - return ERR_PTR(-ENOTDIR); - } + if (!*s) + return ERR_PTR(-EINVAL); - nd->path = f.file->f_path; - if (flags & LOOKUP_RCU) { - nd->inode = nd->path.dentry->d_inode; - nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq); + if (flags & LOOKUP_RCU) { + do { + seq = read_seqcount_begin(&c->seq); + nd->path = c->root; + nd->inode = nd->path.dentry->d_inode; + nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq); + } while (read_seqcount_retry(&c->seq, seq)); + } else { + spin_lock(&c->lock); + nd->path = c->root; + path_get(&nd->path); + spin_unlock(&c->lock); + nd->inode = nd->path.dentry->d_inode; + } } else { - path_get(&nd->path); - nd->inode = nd->path.dentry->d_inode; + dentry = f.file->f_path.dentry; + + if (*s && unlikely(!d_can_lookup(dentry))) { + fdput(f); + return ERR_PTR(-ENOTDIR); + } + + nd->path = f.file->f_path; + if (flags & LOOKUP_RCU) { + nd->inode = nd->path.dentry->d_inode; + nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq); + } else { + path_get(&nd->path); + nd->inode = nd->path.dentry->d_inode; + } } fdput(f); return s;