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@xxxxxxxxxx>
---
fs/namei.c | 52 ++++++++++++++++++++++++++++++++++++++--------------
1 file changed, 38 insertions(+), 14 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index 0d35760fee00..2f0310a39e60 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2208,23 +2208,47 @@ 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) {
- if (!d_can_lookup(dentry)) {
- fdput(f);
- return ERR_PTR(-ENOTDIR);
+ if (!*s)
+ return ERR_PTR(-EINVAL);
+
+ if (flags & LOOKUP_RCU) {
+ rcu_read_lock();
+ 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;
}
- }
-
- nd->path = f.file->f_path;
- if (flags & LOOKUP_RCU) {
- rcu_read_lock();
- 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;
+ dentry = f.file->f_path.dentry;
+
+ if (*s) {
+ if (!d_can_lookup(dentry)) {
+ fdput(f);
+ return ERR_PTR(-ENOTDIR);
+ }
+ }
+
+ nd->path = f.file->f_path;
+ if (flags & LOOKUP_RCU) {
+ rcu_read_lock();
+ 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;
--
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