The patch titled
r/o bind mounts: tricky: elevate write count files are open()ed
has been added to the -mm tree. Its filename is
ro-bind-mounts-tricky-elevate-write-count-files-are-opened.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: r/o bind mounts: tricky: elevate write count files are open()ed
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.
This is not completely apparent in the patch because the two if() conditions
in may_open() above the mnt_want_write() call are, combined, equivalent to
special_file().
There is also an elevated count around the vfs_create() call in open_namei().
The count needs to be kept elevated all the way into the may_open() call.
Otherwise, when the write is dropped, a ro->rw transisition could occur. This
would lead to having rw access on the newly created file, while the vfsmount
is ro. That is bad.
Signed-off-by: Dave Hansen <haveblue@xxxxxxxxxx>
Cc: Serge Hallyn <serue@xxxxxxxxxx>
Cc: Herbert Poetzl <herbert@xxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
fs/file_table.c | 5 ++++-
fs/namei.c | 22 ++++++++++++++++++----
ipc/mqueue.c | 3 +++
3 files changed, 25 insertions(+), 5 deletions(-)
diff -puN fs/file_table.c~ro-bind-mounts-tricky-elevate-write-count-files-are-opened fs/file_table.c
--- a/fs/file_table.c~ro-bind-mounts-tricky-elevate-write-count-files-are-opened
+++ a/fs/file_table.c
@@ -180,8 +180,11 @@ void fastcall __fput(struct file *file)
if (unlikely(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);
+ }
file_kill(file);
file->f_dentry = NULL;
file->f_vfsmnt = NULL;
diff -puN fs/namei.c~ro-bind-mounts-tricky-elevate-write-count-files-are-opened fs/namei.c
--- a/fs/namei.c~ro-bind-mounts-tricky-elevate-write-count-files-are-opened
+++ a/fs/namei.c
@@ -1532,8 +1532,17 @@ int may_open(struct nameidata *nd, int a
return -EACCES;
flag &= ~O_TRUNC;
- } else if (IS_RDONLY(inode) && (flag & FMODE_WRITE))
- return -EROFS;
+ } else if (flag & FMODE_WRITE) {
+ /*
+ * effectively: !special_file()
+ * balanced by __fput()
+ */
+ error = mnt_want_write(nd->mnt);
+ if (error)
+ return error;
+ if (IS_RDONLY(inode))
+ return -EROFS;
+ }
/*
* An append-only file must be opened in append mode for writing.
*/
@@ -1672,14 +1681,17 @@ 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 = mnt_want_write(nd->mnt);
+ if (error)
+ goto exit_mutex_unlock;
error = open_namei_create(nd, &path, flag, mode);
+ mnt_drop_write(nd->mnt);
if (error)
goto exit;
return 0;
@@ -1715,6 +1727,8 @@ ok:
goto exit;
return 0;
+exit_mutex_unlock:
+ mutex_unlock(&dir->d_inode->i_mutex);
exit_dput:
dput_path(&path, nd);
exit:
diff -puN ipc/mqueue.c~ro-bind-mounts-tricky-elevate-write-count-files-are-opened ipc/mqueue.c
--- a/ipc/mqueue.c~ro-bind-mounts-tricky-elevate-write-count-files-are-opened
+++ a/ipc/mqueue.c
@@ -686,6 +686,9 @@ 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
origin.patch
catch-notification-of-memory-add-event-of-acpi-via-container-driver-register-start-func-for-memory-device.patch
catch-notification-of-memory-add-event-of-acpi-via-container-driveravoid-redundant-call-add_memory.patch
pgdat-allocation-for-new-node-add-specify-node-id.patch
pgdat-allocation-for-new-node-add-get-node-id-by-acpi.patch
pgdat-allocation-for-new-node-add-generic-alloc-node_data.patch
pgdat-allocation-for-new-node-add-refresh-node_data.patch
pgdat-allocation-for-new-node-add-export-kswapd-start-func.patch
pgdat-allocation-for-new-node-add-call-pgdat-allocation.patch
node-hotplug-register-cpu-remove-node-struct.patch
acpi-dock-driver.patch
ro-bind-mounts-prepare-for-write-access-checks-collapse-if.patch
ro-bind-mounts-r-o-bind-mount-prepwork-move-open_nameis-vfs_create.patch
ro-bind-mounts-add-vfsmount-writer-count.patch
ro-bind-mounts-elevate-mnt-writers-for-callers-of-vfs_mkdir.patch
ro-bind-mounts-elevate-write-count-during-entire-ncp_ioctl.patch
ro-bind-mounts-sys_symlinkat-elevate-write-count-around-vfs_symlink.patch
ro-bind-mounts-elevate-mount-count-for-extended-attributes.patch
ro-bind-mounts-sys_linkat-elevate-write-count-around-vfs_link.patch
ro-bind-mounts-mount_is_safe-add-comment.patch
ro-bind-mounts-unix_find_other-elevate-write-count-for-touch_atime.patch
ro-bind-mounts-elevate-write-count-over-calls-to-vfs_rename.patch
ro-bind-mounts-tricky-elevate-write-count-files-are-opened.patch
ro-bind-mounts-elevate-writer-count-for-do_sys_truncate.patch
ro-bind-mounts-elevate-write-count-for-do_utimes.patch
ro-bind-mounts-elevate-write-count-for-do_sys_utime-and-touch_atime.patch
ro-bind-mounts-sys_mknodat-elevate-write-count-for-vfs_mknod-create.patch
ro-bind-mounts-elevate-mnt-writers-for-vfs_unlink-callers.patch
ro-bind-mounts-do_rmdir-elevate-write-count.patch
ro-bind-mounts-elevate-writer-count-for-custom-struct-file.patch
ro-bind-mounts-honor-r-w-changes-at-do_remount-time.patch
page-owner-tracking-leak-detector.patch
x86-e820-debugging.patch
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