The patch titled
r-o-bind-mounts: elevate write count opened files
has been removed from the -mm tree. Its filename was
r-o-bind-mounts-elevate-write-count-opened-files.patch
This patch was dropped because an updated version will be merged
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: r-o-bind-mounts: elevate write count opened files
From: Dave Hansen <haveblue@xxxxxxxxxx>
This is the first really tricky patch in the series. It elevates the writer
count on a mount each time a non-special file is opened for write.
We used to do this in may_open(), but Miklos pointed out that __dentry_open()
is used as well to create filps. This will cover even those cases, while a
call in may_open() would not have.
There is also an elevated count around the vfs_create() call in open_namei().
See the comments for more details, but we need this to fix a 'create, remount,
fail r/w open()' race.
Some filesystems forego the use of normal vfs calls to create
struct files. Make sure that these users elevate the mnt
writer count because they will get __fput(), and we need
to make sure they're balanced.
[akpm@xxxxxxxxxxxxxxxxxxxx: fix oops]
Signed-off-by: Dave Hansen <haveblue@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/file_table.c | 16 +++++++++
fs/namei.c | 75 +++++++++++++++++++++++++++++++++++++++-------
fs/open.c | 36 ++++++++++++++++++++--
ipc/mqueue.c | 3 +
4 files changed, 117 insertions(+), 13 deletions(-)
diff -puN fs/file_table.c~r-o-bind-mounts-elevate-write-count-opened-files fs/file_table.c
--- a/fs/file_table.c~r-o-bind-mounts-elevate-write-count-opened-files
+++ a/fs/file_table.c
@@ -193,6 +193,17 @@ int init_file(struct file *file, struct
file->f_mapping = dentry->d_inode->i_mapping;
file->f_mode = mode;
file->f_op = fop;
+
+ /*
+ * These mounts don't really matter in practice
+ * for r/o bind mounts. They aren't userspace-
+ * visible. We do this for consistency, and so
+ * that we can do debugging checks at __fput()e
+ */
+ if ((mode & FMODE_WRITE) && !special_file(dentry->d_inode->i_mode)) {
+ error = mnt_want_write(mnt);
+ WARN_ON(error);
+ }
return error;
}
EXPORT_SYMBOL(init_file);
@@ -230,8 +241,11 @@ void __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)
+ if (file->f_mode & FMODE_WRITE) {
put_write_access(inode);
+ if (!special_file(inode->i_mode))
+ mnt_drop_write(mnt);
+ }
put_pid(file->f_owner.pid);
file_kill(file);
file->f_path.dentry = NULL;
diff -puN fs/namei.c~r-o-bind-mounts-elevate-write-count-opened-files fs/namei.c
--- a/fs/namei.c~r-o-bind-mounts-elevate-write-count-opened-files
+++ a/fs/namei.c
@@ -1621,8 +1621,7 @@ int may_open(struct nameidata *nd, int a
return -EACCES;
flag &= ~O_TRUNC;
- } else if (IS_RDONLY(inode) && (acc_mode & MAY_WRITE))
- return -EROFS;
+ }
error = vfs_permission(nd, acc_mode);
if (error)
@@ -1722,23 +1721,37 @@ static inline int sys_open_flags_to_name
return flag;
}
+static int open_will_write_to_fs(int flag, struct inode *inode)
+{
+ /*
+ * We'll never write to the fs underlying
+ * a device file.
+ */
+ if (special_file(inode->i_mode))
+ return 0;
+ return (flag & O_TRUNC);
+}
+
/*
* open_pathname()
*
* namei for open - this is in fact almost the whole open-routine.
*
- * Note that the low bits of "flag" aren't the same as in the open
- * system call. See sys_open_flags_to_namei_flags().
+ * Note that the low bits of the passed in "sys_open_flag"
+ * are not the same as in the local variable "flag". See
+ * sys_open_flags_to_namei_flags() for more details.
* SMP-safe
*/
struct file *open_pathname(int dfd, const char *pathname,
int sys_open_flag, int mode)
{
+ struct file *filp;
struct nameidata nd;
int acc_mode, error;
struct path path;
struct dentry *dir;
int count = 0;
+ int will_write;
int flag = sys_open_flags_to_namei_flags(sys_open_flag);
acc_mode = ACC_MODE(flag);
@@ -1794,17 +1807,30 @@ do_last:
}
if (IS_ERR(nd.intent.open.file)) {
- mutex_unlock(&dir->d_inode->i_mutex);
error = PTR_ERR(nd.intent.open.file);
- goto exit_dput;
+ goto exit_mutex_unlock;
}
/* Negative dentry, just create the file */
if (!path.dentry->d_inode) {
- error = __open_namei_create(&nd, &path, flag, mode);
+ /*
+ * This write is needed to ensure that a
+ * ro->rw transition does not occur between
+ * the time when the file is created and when
+ * a permanent write count is taken through
+ * the 'struct file' in nameidata_to_filp().
+ */
+ error = mnt_want_write(nd.mnt);
if (error)
+ goto exit_mutex_unlock;
+ error = __open_namei_create(&nd, &path, flag, mode);
+ if (error) {
+ mnt_drop_write(nd.mnt);
goto exit;
- return nameidata_to_filp(&nd, sys_open_flag);
+ }
+ filp = nameidata_to_filp(&nd, sys_open_flag);
+ mnt_drop_write(nd.mnt);
+ return filp;
}
/*
@@ -1834,11 +1860,40 @@ do_last:
if (path.dentry->d_inode && S_ISDIR(path.dentry->d_inode->i_mode))
goto exit;
ok:
+ /*
+ * Consider:
+ * 1. may_open() truncates a file
+ * 2. a rw->ro mount transition occurs
+ * 3. nameidata_to_filp() fails due to
+ * the ro mount.
+ * That would be inconsistent, and should
+ * be avoided. Taking this mnt write here
+ * ensures that (2) can not occur.
+ */
+ will_write = open_will_write_to_fs(flag, nd.dentry->d_inode);
+ if (will_write) {
+ error = mnt_want_write(nd.mnt);
+ if (error)
+ goto exit;
+ }
error = may_open(&nd, acc_mode, flag);
- if (error)
+ if (error) {
+ if (will_write)
+ mnt_drop_write(nd.mnt);
goto exit;
- return nameidata_to_filp(&nd, sys_open_flag);
+ }
+ filp = nameidata_to_filp(&nd, sys_open_flag);
+ /*
+ * It is now safe to drop the mnt write
+ * because the filp has had a write taken
+ * on its behalf.
+ */
+ if (will_write)
+ mnt_drop_write(nd.mnt);
+ return filp;
+exit_mutex_unlock:
+ mutex_unlock(&dir->d_inode->i_mutex);
exit_dput:
dput_path(&path, &nd);
exit:
diff -puN fs/open.c~r-o-bind-mounts-elevate-write-count-opened-files fs/open.c
--- a/fs/open.c~r-o-bind-mounts-elevate-write-count-opened-files
+++ a/fs/open.c
@@ -734,6 +734,35 @@ out:
return error;
}
+/*
+ * You have to be very careful that these write
+ * counts get cleaned up in error cases and
+ * upon __fput(). This should probably never
+ * be called outside of __dentry_open().
+ */
+static inline int __get_file_write_access(struct inode *inode,
+ struct vfsmount *mnt)
+{
+ int error;
+ error = get_write_access(inode);
+ if (error)
+ return error;
+ /*
+ * Do not take mount writer counts on
+ * special files since no writes to
+ * the mount itself will occur.
+ */
+ if (!special_file(inode->i_mode)) {
+ /*
+ * Balanced in __fput()
+ */
+ error = mnt_want_write(mnt);
+ if (error)
+ put_write_access(inode);
+ }
+ return error;
+}
+
static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
int flags, struct file *f,
int (*open)(struct inode *, struct file *))
@@ -746,7 +775,7 @@ static struct file *__dentry_open(struct
FMODE_PREAD | FMODE_PWRITE;
inode = dentry->d_inode;
if (f->f_mode & FMODE_WRITE) {
- error = get_write_access(inode);
+ error = __get_file_write_access(inode, mnt);
if (error)
goto cleanup_file;
}
@@ -788,8 +817,11 @@ static struct file *__dentry_open(struct
cleanup_all:
fops_put(f->f_op);
- if (f->f_mode & FMODE_WRITE)
+ if (f->f_mode & FMODE_WRITE) {
put_write_access(inode);
+ if (!special_file(inode->i_mode))
+ mnt_drop_write(mnt);
+ }
file_kill(f);
f->f_path.dentry = NULL;
f->f_path.mnt = NULL;
diff -puN ipc/mqueue.c~r-o-bind-mounts-elevate-write-count-opened-files ipc/mqueue.c
--- a/ipc/mqueue.c~r-o-bind-mounts-elevate-write-count-opened-files
+++ a/ipc/mqueue.c
@@ -681,6 +681,9 @@ asmlinkage long sys_mq_open(const char _
goto out;
filp = do_open(dentry, oflag);
} else {
+ error = mnt_want_write(mqueue_mnt);
+ if (error)
+ goto out;
filp = do_create(mqueue_mnt->mnt_root, dentry,
oflag, mode, u_attr);
}
_
Patches currently in -mm which might be from haveblue@xxxxxxxxxx are
enable-hotplug-memory-remove-for-ppc64.patch
r-o-bind-mounts-elevate-write-count-opened-files.patch
r-o-bind-mounts-elevate-write-count-over-calls-to-vfs_rename.patch
r-o-bind-mounts-elevate-writer-count-for-chown-and-friends.patch
r-o-bind-mounts-elevate-writer-count-for-do_sys_truncate.patch
r-o-bind-mounts-make-access-use-mnt-check.patch
r-o-bind-mounts-nfs-check-mnt-instead-of-superblock-directly.patch
r-o-bind-mounts-sys_mknodat-elevate-write-count-for-vfs_mknod-create.patch
r-o-bind-mounts-track-number-of-mount-writers.patch
r-o-bind-mounts-honor-r-w-changes-at-do_remount-time.patch
keep-track-of-mnt_writer-state-of-struct-file.patch
create-file_drop_write_access-helper.patch
fix-up-new-filp-allocators.patch
reiser4.patch
page-owner-tracking-leak-detector.patch
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