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    Subject[PATCH 22/30] r/o bind mounts: elevate write count for chmod/chown callers
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    chown/chmod,etc... don't call permission in the same way that the normal
    "open for write" calls do. They still write to the filesystem, so bump the
    write count during these operations.

    Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
    Signed-off-by: Christoph Hellwig <hch@lst.de>
    Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    ---
    linux-2.6.git-dave/fs/open.c | 39 ++++++++++++++++++++++++++++++---------
    1 file changed, 30 insertions(+), 9 deletions(-)
    diff -puN fs/open.c~r-o-bind-mounts-elevate-writer-count-for-chown-and-friends fs/open.c
    --- linux-2.6.git/fs/open.c~r-o-bind-mounts-elevate-writer-count-for-chown-and-friends 2008-02-15 13:25:55.000000000 -0800
    +++ linux-2.6.git-dave/fs/open.c 2008-02-15 13:25:55.000000000 -0800
    @@ -567,12 +567,12 @@ asmlinkage long sys_fchmod(unsigned int

    audit_inode(NULL, dentry);

    - err = -EROFS;
    - if (IS_RDONLY(inode))
    + err = mnt_want_write(file->f_vfsmnt);
    + if (err)
    goto out_putf;
    err = -EPERM;
    if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
    - goto out_putf;
    + goto out_drop_write;
    mutex_lock(&inode->i_mutex);
    if (mode == (mode_t) -1)
    mode = inode->i_mode;
    @@ -581,6 +581,8 @@ asmlinkage long sys_fchmod(unsigned int
    err = notify_change(dentry, &newattrs);
    mutex_unlock(&inode->i_mutex);

    +out_drop_write:
    + mnt_drop_write(file->f_vfsmnt);
    out_putf:
    fput(file);
    out:
    @@ -600,13 +602,13 @@ asmlinkage long sys_fchmodat(int dfd, co
    goto out;
    inode = nd.path.dentry->d_inode;

    - error = -EROFS;
    - if (IS_RDONLY(inode))
    + error = mnt_want_write(nd.path.mnt);
    + if (error)
    goto dput_and_out;

    error = -EPERM;
    if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
    - goto dput_and_out;
    + goto out_drop_write;

    mutex_lock(&inode->i_mutex);
    if (mode == (mode_t) -1)
    @@ -616,6 +618,8 @@ asmlinkage long sys_fchmodat(int dfd, co
    error = notify_change(nd.path.dentry, &newattrs);
    mutex_unlock(&inode->i_mutex);

    +out_drop_write:
    + mnt_drop_write(nd.path.mnt);
    dput_and_out:
    path_put(&nd.path);
    out:
    @@ -638,9 +642,6 @@ static int chown_common(struct dentry *
    printk(KERN_ERR "chown_common: NULL inode\n");
    goto out;
    }
    - error = -EROFS;
    - if (IS_RDONLY(inode))
    - goto out;
    error = -EPERM;
    if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
    goto out;
    @@ -671,7 +672,12 @@ asmlinkage long sys_chown(const char __u
    error = user_path_walk(filename, &nd);
    if (error)
    goto out;
    + error = mnt_want_write(nd.path.mnt);
    + if (error)
    + goto out_release;
    error = chown_common(nd.path.dentry, user, group);
    + mnt_drop_write(nd.path.mnt);
    +out_release:
    path_put(&nd.path);
    out:
    return error;
    @@ -691,7 +697,12 @@ asmlinkage long sys_fchownat(int dfd, co
    error = __user_walk_fd(dfd, filename, follow, &nd);
    if (error)
    goto out;
    + error = mnt_want_write(nd.path.mnt);
    + if (error)
    + goto out_release;
    error = chown_common(nd.path.dentry, user, group);
    + mnt_drop_write(nd.path.mnt);
    +out_release:
    path_put(&nd.path);
    out:
    return error;
    @@ -705,7 +716,12 @@ asmlinkage long sys_lchown(const char __
    error = user_path_walk_link(filename, &nd);
    if (error)
    goto out;
    + error = mnt_want_write(nd.path.mnt);
    + if (error)
    + goto out_release;
    error = chown_common(nd.path.dentry, user, group);
    + mnt_drop_write(nd.path.mnt);
    +out_release:
    path_put(&nd.path);
    out:
    return error;
    @@ -722,9 +738,14 @@ asmlinkage long sys_fchown(unsigned int
    if (!file)
    goto out;

    + error = mnt_want_write(file->f_vfsmnt);
    + if (error)
    + goto out_fput;
    dentry = file->f_path.dentry;
    audit_inode(NULL, dentry);
    error = chown_common(dentry, user, group);
    + mnt_drop_write(file->f_vfsmnt);
    +out_fput:
    fput(file);
    out:
    return error;
    _

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