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Message-ID: <20160323133606.GF11906@tucsk>
Date: Wed, 23 Mar 2016 14:36:06 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-unionfs@...r.kernel.org, David Howells <dhowells@...hat.com>,
Goldwyn Rodrigues <rgoldwyn@...e.com>,
Trond Myklebust <trond.myklebust@...marydata.com>,
Theodore Ts'o <tytso@....edu>, Daniel Axtens <dja@...ens.net>,
stable@...r.kernel.org
Subject: [PATCH v2] fs: add file_dentry()
This series fixes bugs in nfs and ext4 due to 4bacc9c9234c ("overlayfs:
Make f_path always point to the overlay and f_inode to the underlay").
Regular files opened on overlayfs will result in the file being opened on
the underlying filesystem, while f_path points to the overlayfs
mount/dentry.
This confuses filesystems which get the dentry from struct file and assume
it's theirs.
Add a new helper, file_dentry() [*], to get the filesystem's own dentry
from the file. This checks file->f_path.dentry->d_flags against
DCACHE_OP_REAL, and returns file->f_path.dentry if DCACHE_OP_REAL is not
set (this is the common, non-overlayfs case).
In the uncommon case it will call into overlayfs's ->d_real() to get the
underlying dentry, matching file_inode(file).
The reason we need to check against the inode is that if the file is copied
up while being open, d_real() would return the upper dentry, while the open
file comes from the lower dentry.
[*] If possible, it's better simply to use file_inode() instead.
Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
Tested-by: Goldwyn Rodrigues <rgoldwyn@...e.com>
Reviewed-by: Trond Myklebust <trond.myklebust@...marydata.com>
Cc: <stable@...r.kernel.org> # v4.2
Cc: David Howells <dhowells@...hat.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Theodore Ts'o <tytso@....edu>
Cc: Daniel Axtens <dja@...ens.net>
---
changes in v2:
- rename method to d_op->d_real()
- check d_flag instead of comparing inode for base dentry
- ovl_d_real() now handles recursion
- WARN instead of BUG and be more verbose
- add d_real() helper too
fs/dcache.c | 5 ++++-
fs/overlayfs/super.c | 33 +++++++++++++++++++++++++++++++++
include/linux/dcache.h | 10 ++++++++++
include/linux/fs.h | 10 ++++++++++
4 files changed, 57 insertions(+), 1 deletion(-)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1667,7 +1667,8 @@ void d_set_d_op(struct dentry *dentry, c
DCACHE_OP_REVALIDATE |
DCACHE_OP_WEAK_REVALIDATE |
DCACHE_OP_DELETE |
- DCACHE_OP_SELECT_INODE));
+ DCACHE_OP_SELECT_INODE |
+ DCACHE_OP_REAL));
dentry->d_op = op;
if (!op)
return;
@@ -1685,6 +1686,8 @@ void d_set_d_op(struct dentry *dentry, c
dentry->d_flags |= DCACHE_OP_PRUNE;
if (op->d_select_inode)
dentry->d_flags |= DCACHE_OP_SELECT_INODE;
+ if (op->d_real)
+ dentry->d_flags |= DCACHE_OP_REAL;
}
EXPORT_SYMBOL(d_set_d_op);
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -161,6 +161,7 @@ struct dentry_operations {
struct vfsmount *(*d_automount)(struct path *);
int (*d_manage)(struct dentry *, bool);
struct inode *(*d_select_inode)(struct dentry *, unsigned);
+ struct dentry *(*d_real)(struct dentry *, struct inode *);
} ____cacheline_aligned;
/*
@@ -229,6 +230,7 @@ struct dentry_operations {
#define DCACHE_OP_SELECT_INODE 0x02000000 /* Unioned entry: dcache op selects inode */
#define DCACHE_ENCRYPTED_WITH_KEY 0x04000000 /* dir is encrypted with a valid key */
+#define DCACHE_OP_REAL 0x08000000
extern seqlock_t rename_lock;
@@ -555,4 +557,12 @@ static inline struct dentry *d_backing_d
return upper;
}
+static inline struct dentry *d_real(struct dentry *dentry)
+{
+ if (unlikely(dentry->d_flags & DCACHE_OP_REAL))
+ return dentry->d_op->d_real(dentry, NULL);
+ else
+ return dentry;
+}
+
#endif /* __LINUX_DCACHE_H */
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -295,6 +295,37 @@ static void ovl_dentry_release(struct de
}
}
+static struct dentry *ovl_d_real(struct dentry *dentry, struct inode *inode)
+{
+ struct dentry *real;
+
+ if (d_is_dir(dentry)) {
+ if (!inode || inode == d_inode(dentry))
+ return dentry;
+ goto bug;
+ }
+
+ real = ovl_dentry_upper(dentry);
+ if (real && (!inode || inode == d_inode(real)))
+ return real;
+
+ real = ovl_dentry_lower(dentry);
+ if (!real)
+ goto bug;
+
+ if (!inode || inode == d_inode(real))
+ return real;
+
+ /* Handle recursion */
+ if (real->d_flags & DCACHE_OP_REAL)
+ return real->d_op->d_real(real, inode);
+
+bug:
+ WARN(1, "ovl_d_real(%pd4, %s:%lu\n): real dentry not found\n", dentry,
+ inode ? inode->i_sb->s_id : "NULL", inode ? inode->i_ino : 0);
+ return dentry;
+}
+
static int ovl_dentry_revalidate(struct dentry *dentry, unsigned int flags)
{
struct ovl_entry *oe = dentry->d_fsdata;
@@ -339,11 +370,13 @@ static int ovl_dentry_weak_revalidate(st
static const struct dentry_operations ovl_dentry_operations = {
.d_release = ovl_dentry_release,
.d_select_inode = ovl_d_select_inode,
+ .d_real = ovl_d_real,
};
static const struct dentry_operations ovl_reval_dentry_operations = {
.d_release = ovl_dentry_release,
.d_select_inode = ovl_d_select_inode,
+ .d_real = ovl_d_real,
.d_revalidate = ovl_dentry_revalidate,
.d_weak_revalidate = ovl_dentry_weak_revalidate,
};
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1241,6 +1241,16 @@ static inline struct inode *file_inode(c
return f->f_inode;
}
+static inline struct dentry *file_dentry(const struct file *file)
+{
+ struct dentry *dentry = file->f_path.dentry;
+
+ if (unlikely(dentry->d_flags & DCACHE_OP_REAL))
+ return dentry->d_op->d_real(dentry, file_inode(file));
+ else
+ return dentry;
+}
+
static inline int locks_lock_file_wait(struct file *filp, struct file_lock *fl)
{
return locks_lock_inode_wait(file_inode(filp), fl);
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