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Message-ID: <20160427101137.GA14826@veci.piliscsaba.szeredi.hu>
Date: Wed, 27 Apr 2016 12:11:37 +0200
From: Miklos Szeredi <miklos@...redi.hu>
To: Sasha Levin <sasha.levin@...cle.com>
Cc: Al Viro <viro@...iv.linux.org.uk>, 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,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2] fs: add file_dentry()
On Wed, Apr 20, 2016 at 01:07:16AM -0400, Sasha Levin wrote:
> Hey Miklos,
>
> On 03/23/2016 09:36 AM, Miklos Szeredi wrote:
> > 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").
>
> Since that commit got backported into older -stable kernel, it would
> appear that this file_dentry() series is relevant for pre-4.2 kernels as
> well.
>
> However, backporting it seems to be less than trivial.
>
> Could you provide a backport for older -stable kernels please?
From: Miklos Szeredi <miklos@...redi.hu>
Date: Sat, 26 Mar 2016 16:14:37 -0400
Subject: fs: add file_dentry()
commit d101a125954eae1d397adda94ca6319485a50493 upstream.
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>
Signed-off-by: Theodore Ts'o <tytso@....edu>
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: Daniel Axtens <dja@...ens.net>
---
fs/dcache.c | 5 ++++-
fs/overlayfs/super.c | 32 ++++++++++++++++++++++++++++++++
include/linux/dcache.h | 10 ++++++++++
include/linux/fs.h | 10 ++++++++++
4 files changed, 56 insertions(+), 1 deletion(-)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1666,7 +1666,8 @@ 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;
@@ -1684,6 +1685,8 @@ 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/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -276,9 +276,41 @@ 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 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 struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
--- 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;
/*
@@ -227,6 +228,7 @@ 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 */
+#define DCACHE_OP_REAL 0x08000000
extern seqlock_t rename_lock;
@@ -576,4 +578,12 @@ 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/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1199,6 +1199,16 @@ 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 posix_lock_file_wait(struct file *filp, struct file_lock *fl)
{
return posix_lock_inode_wait(file_inode(filp), fl);
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