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fs: add file_dentry()

PATCH In review Miklos Szeredi 3 participants 6 messages Mar 23, 2016 – Apr 27, 2016

Subsystems (3)
Stable branch VFS Overlay filesystem
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Miklos Szeredi

author maintainer
#0 lore raw

PATCH v2 1/1 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 <[email protected]>
Tested-by Goldwyn Rodrigues <[email protected]>
Reviewed-by Trond Myklebust <[email protected]>
Cc <[email protected]> # v4.2
Cc David Howells <[email protected]>
Cc Al Viro <[email protected]>
Cc Theodore Ts'o <[email protected]>
Cc Daniel Axtens <[email protected]>

---
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(-)
fs/dcache.c +4 -1
@@ -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);
include/linux/dcache.h +10 -0
@@ -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 */
fs/overlayfs/super.c +33 -0
@@ -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,
 };
include/linux/fs.h +10 -0
@@ -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);
#1 lore raw

Hello Miklos,

Quoted 22 lines · Miklos Szeredi

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.

Quoted 6 lines

[*] If possible, it's better simply to use file_inode() instead.

Signed-off-by Miklos Szeredi <[email protected]>
Tested-by Goldwyn Rodrigues <[email protected]>
Reviewed-by Trond Myklebust <[email protected]>
Cc <[email protected]> # v4.2

4bacc9c9234c ("overlayfs: Make f_path always point to the overlay and f_inode to the underlay").
This commit is from v4.1 if I am not wrong. So the stable tag might be wrong.

Am I missing something?

Signature · 1 line
William
author maintainer
#2 lore raw
Quoted 5 lines · William Dauchy

4bacc9c9234c ("overlayfs: Make f_path always point to the overlay and f_inode to the underlay").
This commit is from v4.1 if I am not wrong. So the stable tag might be wrong.

Am I missing something?

Use "--contains", otherwise "git describe" will just say which kernel the patch has been committed to, not which release it appears in.

git describe --contains 4bacc9c9234c
v4.2-rc1~2^2~27

Thanks,
Miklos

#4 lore raw
In reply to Miklos Szeredi

Hey Miklos,

Quoted 2 lines · Miklos Szeredi

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?

Thanks,
Sasha

author maintainer Tested-by Goldwyn Rodrigues Reviewed-by Trond Myklebust
#5 lore raw
Quoted 6 lines · Sasha Levin

Hey Miklos,

Quoted 2 lines · Miklos Szeredi

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").

Quoted 7 lines

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 <[email protected]>
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 <[email protected]>
Signed-off-by Theodore Ts'o <[email protected]>
Tested-by Goldwyn Rodrigues <[email protected]>
Reviewed-by Trond Myklebust <[email protected]>
Cc <[email protected]> # v4.2
Cc David Howells <[email protected]>
Cc Al Viro <[email protected]>
Cc Daniel Axtens <[email protected]>
---
 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(-)
fs/dcache.c +4 -1
@@ -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);
fs/overlayfs/super.c +32 -0
@@ -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)
include/linux/dcache.h +10 -0
@@ -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 */
include/linux/fs.h +10 -0
@@ -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);