overlayfs: Make f_path always point to the overlay and f_inode to the underlay
Make file->f_path always point to the overlay dentry so that the path in
/proc/pid/fd is correct and to ensure that label-based LSMs have access to the
overlay as well as the underlay (path-based LSMs probably don't need it).
Using my union testsuite to set things up, before the patch I see:
[root@andromeda union-testsuite]# bash 5</mnt/a/foo107
[root@andromeda union-testsuite]# ls -l /proc/$$/fd/
...
lr-x------. 1 root root 64 Jun 5 14:38 5 -> /a/foo107
[root@andromeda union-testsuite]# stat /mnt/a/foo107
...
Device: 23h/35d Inode: 13381 Links: 1
...
[root@andromeda union-testsuite]# stat -L /proc/$$/fd/5
...
Device: 23h/35d Inode: 13381 Links: 1
...
After the patch:
[root@andromeda union-testsuite]# bash 5</mnt/a/foo107
[root@andromeda union-testsuite]# ls -l /proc/$$/fd/
...
lr-x------. 1 root root 64 Jun 5 14:22 5 -> /mnt/a/foo107
[root@andromeda union-testsuite]# stat /mnt/a/foo107
...
Device: 23h/35d Inode: 40346 Links: 1
...
[root@andromeda union-testsuite]# stat -L /proc/$$/fd/5
...
Device: 23h/35d Inode: 40346 Links: 1
...
Note the change in where /proc/$$/fd/5 points to in the ls command. It was
pointing to /a/foo107 (which doesn't exist) and now points to /mnt/a/foo107
(which is correct).
The inode accessed, however, is the lower layer. The union layer is on device
25h/37d and the upper layer on 24h/36d.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/open.c b/fs/open.c
index e0250bd..b1c5823 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -678,18 +678,18 @@
}
static int do_dentry_open(struct file *f,
+ struct inode *inode,
int (*open)(struct inode *, struct file *),
const struct cred *cred)
{
static const struct file_operations empty_fops = {};
- struct inode *inode;
int error;
f->f_mode = OPEN_FMODE(f->f_flags) | FMODE_LSEEK |
FMODE_PREAD | FMODE_PWRITE;
path_get(&f->f_path);
- inode = f->f_inode = f->f_path.dentry->d_inode;
+ f->f_inode = inode;
f->f_mapping = inode->i_mapping;
if (unlikely(f->f_flags & O_PATH)) {
@@ -793,7 +793,8 @@
BUG_ON(*opened & FILE_OPENED); /* once it's opened, it's opened */
file->f_path.dentry = dentry;
- error = do_dentry_open(file, open, current_cred());
+ error = do_dentry_open(file, d_backing_inode(dentry), open,
+ current_cred());
if (!error)
*opened |= FILE_OPENED;
@@ -822,6 +823,28 @@
}
EXPORT_SYMBOL(finish_no_open);
+/**
+ * vfs_open - open the file at the given path
+ * @path: path to open
+ * @file: newly allocated file with f_flag initialized
+ * @cred: credentials to use
+ */
+int vfs_open(const struct path *path, struct file *file,
+ const struct cred *cred)
+{
+ struct dentry *dentry = path->dentry;
+ struct inode *inode = dentry->d_inode;
+
+ file->f_path = *path;
+ if (dentry->d_flags & DCACHE_OP_SELECT_INODE) {
+ inode = dentry->d_op->d_select_inode(dentry, file->f_flags);
+ if (IS_ERR(inode))
+ return PTR_ERR(inode);
+ }
+
+ return do_dentry_open(file, inode, NULL, cred);
+}
+
struct file *dentry_open(const struct path *path, int flags,
const struct cred *cred)
{
@@ -853,26 +876,6 @@
}
EXPORT_SYMBOL(dentry_open);
-/**
- * vfs_open - open the file at the given path
- * @path: path to open
- * @filp: newly allocated file with f_flag initialized
- * @cred: credentials to use
- */
-int vfs_open(const struct path *path, struct file *filp,
- const struct cred *cred)
-{
- struct inode *inode = path->dentry->d_inode;
-
- if (inode->i_op->dentry_open)
- return inode->i_op->dentry_open(path->dentry, filp, cred);
- else {
- filp->f_path = *path;
- return do_dentry_open(filp, NULL, cred);
- }
-}
-EXPORT_SYMBOL(vfs_open);
-
static inline int build_open_flags(int flags, umode_t mode, struct open_flags *op)
{
int lookup_flags = 0;