create file_drop_write_access() helper

PATCH In review Dave Hansen 4 participants 6 messages Nov 9, 2007 – Nov 10, 2007

Subsystems (2)

VFS NFS server

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Dave Hansen

author

2007-11-09 21:05 UTC #0 lore raw

PATCH 1/2 create file_drop_write_access() helper

These should fix the bug that Erez Zadok <[email protected]> reported:

Stopping RPC idmapd:

kernel: __fput() of writeable file with no mnt_want_write()
kernel: WARNING: at fs/file_table.c:262 __fput()
kernel:  [<c010283e>] show_trace_log_lvl+0x12/0x25
kernel:  [<c0103042>] show_trace+0xd/0x10

...

The actual bug was a missed mnt_want_write() when a filp was allocated with get_empty_filp() and then made writable. Using alloc_file(), instead, fixes that.

If someone decides to demote a file from r/w to just r/o, they can use this same code as __fput().

NFS does just that, and will use this in the next patch.

Signed-off-by Dave Hansen <[email protected]>

---

 linux-2.6.git-dave/fs/file_table.c      |   46 +++++++++++++++++++++-----------
 linux-2.6.git-dave/include/linux/file.h |    1 
 2 files changed, 32 insertions(+), 15 deletions(-)

fs/file_table.c renamed from fs/file_table.c~create-file_drop_write_access +31 ~~-15~~

diff -puN fs/file_table.c~create-file_drop_write_access fs/file_table.c
@@ -223,6 +223,34 @@ void fastcall fput(struct file *file)
 
 EXPORT_SYMBOL(fput);
 
+/**
+ * drop_file_write_access - give up ability to write to a file
+ * @file: the file to which we will stop writing
+ *
+ * This is a central place which will give up the ability
+ * to write to @file, along with access to write through
+ * its vfsmount.
+ */
+void drop_file_write_access(struct file *file)
+{
+	struct dentry *dentry = file->f_path.dentry;
+	struct vfsmount *mnt = file->f_path.mnt;
+	struct inode *inode = dentry->d_inode;
+
+	put_write_access(inode);
+	if (!special_file(inode->i_mode)) {
+		if (file->f_mnt_write_state == FILE_MNT_WRITE_TAKEN) {
+			mnt_drop_write(mnt);
+			file->f_mnt_write_state |= FILE_MNT_WRITE_RELEASED;
+		} else {
+			printk(KERN_WARNING "dropping write access on "
+					"file with no mnt_want_write()\n");
+			WARN_ON(1);
+		}
+	}
+}
+EXPORT_SYMBOL_GPL(drop_file_write_access);
+
 /* __fput is called from task context when aio completion releases the last
  * last use of a struct file *.  Do not use otherwise.
  */

@@ -248,21 +276,9 @@ void fastcall __fput(struct file *file)
 	if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL))
 		cdev_put(inode->i_cdev);
 	fops_put(file->f_op);
-	if (file->f_mode & FMODE_WRITE) {
-		put_write_access(inode);
-		if (!special_file(inode->i_mode)) {
-			if (file->f_mnt_write_state == FILE_MNT_WRITE_TAKEN) {
-				mnt_drop_write(mnt);
-				file->f_mnt_write_state |=
-					FILE_MNT_WRITE_RELEASED;
-			} else {
-				printk(KERN_WARNING "__fput() of writeable "
-						"file with no "
-						"mnt_want_write()\n");
-				WARN_ON(1);
-			}
-		}
-	}
+	if (file->f_mode & FMODE_WRITE)
+		drop_file_write_access(file);
+
 	put_pid(file->f_owner.pid);
 	file_kill(file);
 	file->f_path.dentry = NULL;

include/linux/file.h renamed from include/linux/file.h~create-file_drop_write_access +1 -0

diff -puN include/linux/file.h~create-file_drop_write_access include/linux/file.h
@@ -61,6 +61,7 @@ extern struct kmem_cache *filp_cachep;
 
 extern void FASTCALL(__fput(struct file *));
 extern void FASTCALL(fput(struct file *));
+extern void drop_file_write_access(struct file *file);
 
 struct file_operations;
 struct vfsmount;

Dave Hansen

author

2007-11-09 21:05 UTC #1 lore raw

PATCH 2/2 fix up new filp allocators

Some new uses of get_empty_filp() have crept in, and are not properly taking mnt_want_write()s. This fixes them up.

We really need to kill get_empty_filp().

Signed-off-by Dave Hansen <[email protected]>

---

 linux-2.6.git-dave/fs/anon_inodes.c    |   16 ++++++----------
 linux-2.6.git-dave/fs/file_table.c     |    6 ++++++
 linux-2.6.git-dave/fs/nfsd/nfs4state.c |    3 ++-
 linux-2.6.git-dave/fs/pipe.c           |   17 +++++++----------
 4 files changed, 21 insertions(+), 21 deletions(-)

fs/anon_inodes.c renamed from fs/anon_inodes.c~fix-idmapd-bug +6 ~~-10~~

diff -puN fs/anon_inodes.c~fix-idmapd-bug fs/anon_inodes.c
@@ -81,13 +81,10 @@ int anon_inode_getfd(int *pfd, struct in
 
 	if (IS_ERR(anon_inode_inode))
 		return -ENODEV;
-	file = get_empty_filp();
-	if (!file)
-		return -ENFILE;
 
 	error = get_unused_fd();
 	if (error < 0)
-		goto err_put_filp;
+		return error;
 	fd = error;
 
 	/*

@@ -114,14 +111,15 @@ int anon_inode_getfd(int *pfd, struct in
 	dentry->d_flags &= ~DCACHE_UNHASHED;
 	d_instantiate(dentry, anon_inode_inode);
 
-	file->f_path.mnt = mntget(anon_inode_mnt);
-	file->f_path.dentry = dentry;
+	error = -ENFILE;
+	file = alloc_file(anon_inode_mnt, dentry,
+			  FMODE_READ | FMODE_WRITE, fops);
+	if (!file)
+		goto err_put_unused_fd;
 	file->f_mapping = anon_inode_inode->i_mapping;
 
 	file->f_pos = 0;
 	file->f_flags = O_RDWR;
-	file->f_op = fops;
-	file->f_mode = FMODE_READ | FMODE_WRITE;
 	file->f_version = 0;
 	file->private_data = priv;

@@ -134,8 +132,6 @@ int anon_inode_getfd(int *pfd, struct in
 
 err_put_unused_fd:
 	put_unused_fd(fd);
-err_put_filp:
-	put_filp(file);
 	return error;
 }
 EXPORT_SYMBOL_GPL(anon_inode_getfd);

fs/file_table.c renamed from fs/file_table.c~fix-idmapd-bug +6 -0

diff -puN fs/file_table.c~fix-idmapd-bug fs/file_table.c
@@ -89,6 +89,12 @@ int proc_nr_files(ctl_table *table, int 
 /* Find an unused file structure and return a pointer to it.
  * Returns NULL, if there are no more free file structures or
  * we run out of memory.
+ *
+ * Be very careful using this.  You are responsible for
+ * getting write access to any mount that you might assign
+ * to this filp, if it is opened for write.  If this is not
+ * done, you will imbalance int the mount's writer count
+ * and a warning at __fput() time.
  */
 struct file *get_empty_filp(void)
 {

fs/nfsd/nfs4state.c renamed from fs/nfsd/nfs4state.c~fix-idmapd-bug +2 -1

diff -puN fs/nfsd/nfs4state.c~fix-idmapd-bug fs/nfsd/nfs4state.c
@@ -41,6 +41,7 @@
 #include <linux/sunrpc/svc.h>
 #include <linux/nfsd/nfsd.h>
 #include <linux/nfsd/cache.h>
+#include <linux/file.h>
 #include <linux/mount.h>
 #include <linux/workqueue.h>
 #include <linux/smp_lock.h>

@@ -1303,7 +1304,7 @@ static inline void
 nfs4_file_downgrade(struct file *filp, unsigned int share_access)
 {
 	if (share_access & NFS4_SHARE_ACCESS_WRITE) {
-		put_write_access(filp->f_path.dentry->d_inode);
+		drop_file_write_access(filp);
 		filp->f_mode = (filp->f_mode | FMODE_READ) & ~FMODE_WRITE;
 	}
 }

fs/pipe.c renamed from fs/pipe.c~fix-idmapd-bug +7 ~~-10~~

diff -puN fs/pipe.c~fix-idmapd-bug fs/pipe.c
@@ -959,13 +959,10 @@ struct file *create_write_pipe(void)
 	struct dentry *dentry;
 	struct qstr name = { .name = "" };
 
-	f = get_empty_filp();
-	if (!f)
-		return ERR_PTR(-ENFILE);
 	err = -ENFILE;
 	inode = get_pipe_inode();
 	if (!inode)
-		goto err_file;
+		goto err;
 
 	err = -ENOMEM;
 	dentry = d_alloc(pipe_mnt->mnt_sb->s_root, &name);

@@ -980,13 +977,14 @@ struct file *create_write_pipe(void)
 	 */
 	dentry->d_flags &= ~DCACHE_UNHASHED;
 	d_instantiate(dentry, inode);
-	f->f_path.mnt = mntget(pipe_mnt);
-	f->f_path.dentry = dentry;
+
+	f = alloc_file(pipe_mnt, dentry, FMODE_WRITE, &write_pipe_fops);
+	err = -ENFILE;
+	if (!f)
+		goto err_inode;
 	f->f_mapping = inode->i_mapping;
 
 	f->f_flags = O_WRONLY;
-	f->f_op = &write_pipe_fops;
-	f->f_mode = FMODE_WRITE;
 	f->f_version = 0;
 
 	return f;

@@ -994,8 +992,7 @@ struct file *create_write_pipe(void)
  err_inode:
 	free_pipe_info(inode);
 	iput(inode);
- err_file:
-	put_filp(f);
+ err:
 	return ERR_PTR(err);
 }

Trond Myklebust

2007-11-09 21:23 UTC #2 lore raw

Re: [PATCH 2/2] fix up new filp allocators

Quoted 90 lines · Dave Hansen

Some new uses of get_empty_filp() have crept in, and are not properly taking mnt_want_write()s. This fixes them up.

We really need to kill get_empty_filp().

Signed-off-by Dave Hansen <[email protected]>

---

 linux-2.6.git-dave/fs/anon_inodes.c    |   16 ++++++----------
 linux-2.6.git-dave/fs/file_table.c     |    6 ++++++
 linux-2.6.git-dave/fs/nfsd/nfs4state.c |    3 ++-
 linux-2.6.git-dave/fs/pipe.c           |   17 +++++++----------
 4 files changed, 21 insertions(+), 21 deletions(-)

diff -puN fs/anon_inodes.c~fix-idmapd-bug fs/anon_inodes.c

fs/anon_inodes.c renamed from fs/anon_inodes.c~fix-idmapd-bug +6 ~~-10~~

@@ -81,13 +81,10 @@ int anon_inode_getfd(int *pfd, struct in
 
 	if (IS_ERR(anon_inode_inode))
 		return -ENODEV;
-	file = get_empty_filp();
-	if (!file)
-		return -ENFILE;
 
 	error = get_unused_fd();
 	if (error < 0)
-		goto err_put_filp;
+		return error;
 	fd = error;
 
 	/*

@@ -114,14 +111,15 @@ int anon_inode_getfd(int *pfd, struct in
 	dentry->d_flags &= ~DCACHE_UNHASHED;
 	d_instantiate(dentry, anon_inode_inode);
 
-	file->f_path.mnt = mntget(anon_inode_mnt);
-	file->f_path.dentry = dentry;
+	error = -ENFILE;
+	file = alloc_file(anon_inode_mnt, dentry,
+			  FMODE_READ | FMODE_WRITE, fops);
+	if (!file)
+		goto err_put_unused_fd;
 	file->f_mapping = anon_inode_inode->i_mapping;
 
 	file->f_pos = 0;
 	file->f_flags = O_RDWR;
-	file->f_op = fops;
-	file->f_mode = FMODE_READ | FMODE_WRITE;
 	file->f_version = 0;
 	file->private_data = priv;

@@ -134,8 +132,6 @@ int anon_inode_getfd(int *pfd, struct in
 
 err_put_unused_fd:
 	put_unused_fd(fd);
-err_put_filp:
-	put_filp(file);
 	return error;
 }
 EXPORT_SYMBOL_GPL(anon_inode_getfd);

diff -puN fs/file_table.c~fix-idmapd-bug fs/file_table.c

fs/file_table.c renamed from fs/file_table.c~fix-idmapd-bug +6 -0

@@ -89,6 +89,12 @@ int proc_nr_files(ctl_table *table, int 
 /* Find an unused file structure and return a pointer to it.
  * Returns NULL, if there are no more free file structures or
  * we run out of memory.
+ *
+ * Be very careful using this.  You are responsible for
+ * getting write access to any mount that you might assign
+ * to this filp, if it is opened for write.  If this is not
+ * done, you will imbalance int the mount's writer count
+ * and a warning at __fput() time.
  */
 struct file *get_empty_filp(void)
 {

diff -puN fs/nfsd/nfs4state.c~fix-idmapd-bug fs/nfsd/nfs4state.c

fs/nfsd/nfs4state.c renamed from fs/nfsd/nfs4state.c~fix-idmapd-bug +1 -0

@@ -41,6 +41,7 @@
 #include <linux/sunrpc/svc.h>
 #include <linux/nfsd/nfsd.h>
 #include <linux/nfsd/cache.h>
+#include <linux/file.h>
 #include <linux/mount.h>
 #include <linux/workqueue.h>
 #include <linux/smp_lock.h>

fs/nfsd/nfs4state.c static inline void · line 1310

Quoted 8 lines

fs/nfsd/nfs4state.c renamed from fs/nfsd/nfs4state.c~fix-idmapd-bug +1 -1

@@ -1303,7 +1304,7 @@ static inline void
 nfs4_file_downgrade(struct file *filp, unsigned int share_access)
 {
 	if (share_access & NFS4_SHARE_ACCESS_WRITE) {
-		put_write_access(filp->f_path.dentry->d_inode);
+		drop_file_write_access(filp);
 		filp->f_mode = (filp->f_mode | FMODE_READ) & ~FMODE_WRITE;
 	}
 }

Hmm... The NFS server may also try to 'upgrade' an open file request to a read/write request whenever the client issues a new OPEN request for WRITE using the same open_owner.

Quoted 38 lines

diff -puN fs/pipe.c~fix-idmapd-bug fs/pipe.c

fs/pipe.c renamed from fs/pipe.c~fix-idmapd-bug +6 -8

@@ -959,13 +959,10 @@ struct file *create_write_pipe(void)
 	struct dentry *dentry;
 	struct qstr name = { .name = "" };
 
-	f = get_empty_filp();
-	if (!f)
-		return ERR_PTR(-ENFILE);
 	err = -ENFILE;
 	inode = get_pipe_inode();
 	if (!inode)
-		goto err_file;
+		goto err;
 
 	err = -ENOMEM;
 	dentry = d_alloc(pipe_mnt->mnt_sb->s_root, &name);

@@ -980,13 +977,14 @@ struct file *create_write_pipe(void)
 	 */
 	dentry->d_flags &= ~DCACHE_UNHASHED;
 	d_instantiate(dentry, inode);
-	f->f_path.mnt = mntget(pipe_mnt);
-	f->f_path.dentry = dentry;
+
+	f = alloc_file(pipe_mnt, dentry, FMODE_WRITE, &write_pipe_fops);
+	err = -ENFILE;
+	if (!f)
+		goto err_inode;
 	f->f_mapping = inode->i_mapping;
 
 	f->f_flags = O_WRONLY;
-	f->f_op = &write_pipe_fops;
-	f->f_mode = FMODE_WRITE;
 	f->f_version = 0;
 
 	return f;

fs/pipe.c struct file *create_write_pipe(void) · line 997

Quoted 8 lines

fs/pipe.c renamed from fs/pipe.c~fix-idmapd-bug +1 -2

@@ -994,8 +992,7 @@ struct file *create_write_pipe(void)
  err_inode:
 	free_pipe_info(inode);
 	iput(inode);
- err_file:
-	put_filp(f);
+ err:
 	return ERR_PTR(err);
 }

Does RPC idmapd open a regular pipe too? I thought it only used rpc_pipefs?

Trond

Dave Hansen

author

2007-11-09 21:39 UTC #3 lore raw

Re: [PATCH 2/2] fix up new filp allocators

Quoted 12 lines · Trond Myklebust

Quoted 12 lines
#include <linux/sunrpc/svc.h>
#include <linux/nfsd/nfsd.h>
#include <linux/nfsd/cache.h>
fs/nfsd/nfs4state.c renamed from fs/nfsd/nfs4state.c~fix-idmapd-bug +1 -1
+#include <linux/file.h>
 #include <linux/mount.h>
 #include <linux/workqueue.h>
 #include <linux/smp_lock.h>
@@ -1303,7 +1304,7 @@ static inline void
 nfs4_file_downgrade(struct file *filp, unsigned int share_access)
 {
 	if (share_access & NFS4_SHARE_ACCESS_WRITE) {
-		put_write_access(filp->f_path.dentry->d_inode);

Quoted 8 lines

fs/nfsd/nfs4state.c static inline void · line 1310
Quoted 4 lines
fs/nfsd/nfs4state.c renamed from fs/nfsd/nfs4state.c~fix-idmapd-bug +1 -0
+		drop_file_write_access(filp);
 		filp->f_mode = (filp->f_mode | FMODE_READ) & ~FMODE_WRITE;
 	}
 }
Hmm... The NFS server may also try to 'upgrade' an open file request to a read/write request whenever the client issues a new OPEN request for WRITE using the same open_owner.

Can you point me to some code? I'll try and go fix it up.

Quoted 36 lines

diff -puN fs/pipe.c~fix-idmapd-bug fs/pipe.c

fs/pipe.c renamed from fs/pipe.c~fix-idmapd-bug +6 -8

@@ -959,13 +959,10 @@ struct file *create_write_pipe(void)
 	struct dentry *dentry;
 	struct qstr name = { .name = "" };
 
-	f = get_empty_filp();
-	if (!f)
-		return ERR_PTR(-ENFILE);
 	err = -ENFILE;
 	inode = get_pipe_inode();
 	if (!inode)
-		goto err_file;
+		goto err;
 
 	err = -ENOMEM;
 	dentry = d_alloc(pipe_mnt->mnt_sb->s_root, &name);

@@ -980,13 +977,14 @@ struct file *create_write_pipe(void)
 	 */
 	dentry->d_flags &= ~DCACHE_UNHASHED;
 	d_instantiate(dentry, inode);
-	f->f_path.mnt = mntget(pipe_mnt);
-	f->f_path.dentry = dentry;
+
+	f = alloc_file(pipe_mnt, dentry, FMODE_WRITE, &write_pipe_fops);
+	err = -ENFILE;
+	if (!f)
+		goto err_inode;
 	f->f_mapping = inode->i_mapping;
 
 	f->f_flags = O_WRONLY;
-	f->f_op = &write_pipe_fops;
-	f->f_mode = FMODE_WRITE;
 	f->f_version = 0;

Quoted 13 lines

fs/pipe.c struct file *create_write_pipe(void) · line 997
Quoted 10 lines
fs/pipe.c renamed from fs/pipe.c~fix-idmapd-bug +1 -2
 	return f;
@@ -994,8 +992,7 @@ struct file *create_write_pipe(void)
  err_inode:
 	free_pipe_info(inode);
 	iput(inode);
- err_file:
-	put_filp(f);
+ err:
 	return ERR_PTR(err);
 }
Does RPC idmapd open a regular pipe too? I thought it only used rpc_pipefs?

No. I the the actual bug triggered by idmapd was from an eventpoll filp that had been acquired through anon_inode_getfd(). I just noticed the pipe code here could be another potential bug of the same type.

-- Dave

J. Bruce Fields

2007-11-09 21:46 UTC #4 lore raw

Re: [PATCH 2/2] fix up new filp allocators

Quoted 22 lines · Dave Hansen

Quoted 12 lines · Trond Myklebust
Quoted 12 lines
#include <linux/sunrpc/svc.h>
#include <linux/nfsd/nfsd.h>
#include <linux/nfsd/cache.h>
fs/nfsd/nfs4state.c renamed from fs/nfsd/nfs4state.c~fix-idmapd-bug +1 -1
+#include <linux/file.h>
 #include <linux/mount.h>
 #include <linux/workqueue.h>
 #include <linux/smp_lock.h>
@@ -1303,7 +1304,7 @@ static inline void
 nfs4_file_downgrade(struct file *filp, unsigned int share_access)
 {
 	if (share_access & NFS4_SHARE_ACCESS_WRITE) {
-		put_write_access(filp->f_path.dentry->d_inode);
Quoted 8 lines
fs/nfsd/nfs4state.c static inline void · line 1310
Quoted 4 lines
fs/nfsd/nfs4state.c renamed from fs/nfsd/nfs4state.c~fix-idmapd-bug +1 -0
+		drop_file_write_access(filp);
 		filp->f_mode = (filp->f_mode | FMODE_READ) & ~FMODE_WRITE;
 	}
 }
Hmm... The NFS server may also try to 'upgrade' an open file request to a read/write request whenever the client issues a new OPEN request for WRITE using the same open_owner.

Quoted 1 line

Can you point me to some code? I'll try and go fix it up.

See fs/nfsd/nfs4state.c:nfs4_upgrade_open().

I suspect that there are other reasons why what nfsd is doing here is a bad idea, and that we should really be getting a new file descriptor. But I haven't figured out yet what to do instead.

--b.

Erez Zadok

2007-11-10 02:37 UTC #5 lore raw

In reply to Dave Hansen

Quoted 10 lines · Dave Hansen

These should fix the bug that Erez Zadok <[email protected]> reported:
Stopping RPC idmapd:
kernel: __fput() of writeable file with no mnt_want_write()
kernel: WARNING: at fs/file_table.c:262 __fput()
kernel:  [<c010283e>] show_trace_log_lvl+0x12/0x25
kernel:  [<c0103042>] show_trace+0xd/0x10

Quoted 6 lines

...
The actual bug was a missed mnt_want_write() when a filp was allocated with get_empty_filp() and then made writable. Using alloc_file(), instead, fixes that.

[...]

I can confirm that this patch fixes the bug I reported earlier today.

Thanks,
Erez.