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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>
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dhowells authored and Al Viro committed Jun 18, 2015
1 parent f25801e commit 4bacc9c9234c7c8eec44f5ed4e960d9f96fa0f01
Showing with 41 additions and 34 deletions.
  1. +4 −1 fs/dcache.c
  2. +1 −0 fs/internal.h
  3. +26 −23 fs/open.c
  4. +6 −8 fs/overlayfs/inode.c
  5. +1 −0 fs/overlayfs/overlayfs.h
  6. +1 −0 fs/overlayfs/super.c
  7. +2 −0 include/linux/dcache.h
  8. +0 −2 include/linux/fs.h
View
@@ -1673,7 +1673,8 @@ void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
DCACHE_OP_COMPARE |
DCACHE_OP_REVALIDATE |
DCACHE_OP_WEAK_REVALIDATE |
- DCACHE_OP_DELETE ));
+ DCACHE_OP_DELETE |
+ DCACHE_OP_SELECT_INODE));
dentry->d_op = op;
if (!op)
return;
@@ -1689,6 +1690,8 @@ void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
dentry->d_flags |= DCACHE_OP_DELETE;
if (op->d_prune)
dentry->d_flags |= DCACHE_OP_PRUNE;
+ if (op->d_select_inode)
+ dentry->d_flags |= DCACHE_OP_SELECT_INODE;
}
EXPORT_SYMBOL(d_set_d_op);
View
@@ -107,6 +107,7 @@ extern struct file *do_file_open_root(struct dentry *, struct vfsmount *,
extern long do_handle_open(int mountdirfd,
struct file_handle __user *ufh, int open_flag);
extern int open_check_o_direct(struct file *f);
+extern int vfs_open(const struct path *, struct file *, const struct cred *);
/*
* inode.c
View
@@ -678,18 +678,18 @@ int open_check_o_direct(struct file *f)
}
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 @@ int finish_open(struct file *file, struct dentry *dentry,
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 @@ int finish_no_open(struct file *file, struct dentry *dentry)
}
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 @@ struct file *dentry_open(const struct path *path, int flags,
}
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;
View
@@ -337,31 +337,30 @@ static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
return true;
}
-static int ovl_dentry_open(struct dentry *dentry, struct file *file,
- const struct cred *cred)
+struct inode *ovl_d_select_inode(struct dentry *dentry, unsigned file_flags)
{
int err;
struct path realpath;
enum ovl_path_type type;
type = ovl_path_real(dentry, &realpath);
- if (ovl_open_need_copy_up(file->f_flags, type, realpath.dentry)) {
+ if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) {
err = ovl_want_write(dentry);
if (err)
- return err;
+ return ERR_PTR(err);
- if (file->f_flags & O_TRUNC)
+ if (file_flags & O_TRUNC)
err = ovl_copy_up_last(dentry, NULL, true);
else
err = ovl_copy_up(dentry);
ovl_drop_write(dentry);
if (err)
- return err;
+ return ERR_PTR(err);
ovl_path_upper(dentry, &realpath);
}
- return vfs_open(&realpath, file, cred);
+ return d_backing_inode(realpath.dentry);
}
static const struct inode_operations ovl_file_inode_operations = {
@@ -372,7 +371,6 @@ static const struct inode_operations ovl_file_inode_operations = {
.getxattr = ovl_getxattr,
.listxattr = ovl_listxattr,
.removexattr = ovl_removexattr,
- .dentry_open = ovl_dentry_open,
};
static const struct inode_operations ovl_symlink_inode_operations = {
View
@@ -173,6 +173,7 @@ ssize_t ovl_getxattr(struct dentry *dentry, const char *name,
void *value, size_t size);
ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size);
int ovl_removexattr(struct dentry *dentry, const char *name);
+struct inode *ovl_d_select_inode(struct dentry *dentry, unsigned file_flags);
struct inode *ovl_new_inode(struct super_block *sb, umode_t mode,
struct ovl_entry *oe);
View
@@ -275,6 +275,7 @@ static void ovl_dentry_release(struct dentry *dentry)
static const struct dentry_operations ovl_dentry_operations = {
.d_release = ovl_dentry_release,
+ .d_select_inode = ovl_d_select_inode,
};
static struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
View
@@ -160,6 +160,7 @@ struct dentry_operations {
char *(*d_dname)(struct dentry *, char *, int);
struct vfsmount *(*d_automount)(struct path *);
int (*d_manage)(struct dentry *, bool);
+ struct inode *(*d_select_inode)(struct dentry *, unsigned);
} ____cacheline_aligned;
/*
@@ -225,6 +226,7 @@ struct dentry_operations {
#define DCACHE_MAY_FREE 0x00800000
#define DCACHE_FALLTHRU 0x01000000 /* Fall through to lower layer */
+#define DCACHE_OP_SELECT_INODE 0x02000000 /* Unioned entry: dcache op selects inode */
extern seqlock_t rename_lock;
View
@@ -1641,7 +1641,6 @@ struct inode_operations {
int (*set_acl)(struct inode *, struct posix_acl *, int);
/* WARNING: probably going away soon, do not use! */
- int (*dentry_open)(struct dentry *, struct file *, const struct cred *);
} ____cacheline_aligned;
ssize_t rw_copy_check_uvector(int type, const struct iovec __user * uvector,
@@ -2194,7 +2193,6 @@ extern struct file *file_open_name(struct filename *, int, umode_t);
extern struct file *filp_open(const char *, int, umode_t);
extern struct file *file_open_root(struct dentry *, struct vfsmount *,
const char *, int);
-extern int vfs_open(const struct path *, struct file *, const struct cred *);
extern struct file * dentry_open(const struct path *, int, const struct cred *);
extern int filp_close(struct file *, fl_owner_t id);

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