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    Subject[PATCH 21/23] sys_mknodat(): elevate write count for vfs_mknod/create()
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    This takes care of all of the direct callers of vfs_mknod().
    Since a few of these cases also handle normal file creation
    as well, this also covers some calls to vfs_create().

    So that we don't have to make three mnt_want/drop_write()
    calls inside of the switch statement, we move some of its
    logic outside of the switch.

    Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
    ---

    lxc-dave/fs/namei.c | 32 +++++++++++++++++++++-----------
    lxc-dave/fs/nfsd/vfs.c | 4 ++++
    lxc-dave/net/unix/af_unix.c | 4 ++++
    3 files changed, 29 insertions(+), 11 deletions(-)

    diff -puN fs/namei.c~sys-mknodat-elevate-write-count-for-vfs-mknod-create fs/namei.c
    --- lxc/fs/namei.c~sys-mknodat-elevate-write-count-for-vfs-mknod-create 2007-07-10 12:46:15.000000000 -0700
    +++ lxc-dave/fs/namei.c 2007-07-11 10:10:55.000000000 -0700
    @@ -1912,12 +1912,25 @@ asmlinkage long sys_mknodat(int dfd, con
    if (error)
    goto out;
    dentry = lookup_create(&nd, 0);
    - error = PTR_ERR(dentry);
    -
    + if (IS_ERR(dentry)) {
    + error = PTR_ERR(dentry);
    + goto out_unlock;
    + }
    if (!IS_POSIXACL(nd.dentry->d_inode))
    mode &= ~current->fs->umask;
    - if (!IS_ERR(dentry)) {
    - switch (mode & S_IFMT) {
    + if (S_ISDIR(mode)) {
    + error = -EPERM;
    + goto out_dput;
    + }
    + if (!S_ISREG(mode) && !S_ISCHR(mode) && !S_ISBLK(mode) &&
    + !S_ISFIFO(mode) && !S_ISSOCK(mode) && mode != 0) {
    + error = -EINVAL;
    + goto out_dput;
    + }
    + error = mnt_want_write(nd.mnt);
    + if (error)
    + goto out_dput;
    + switch (mode & S_IFMT) {
    case 0: case S_IFREG:
    error = vfs_create(nd.dentry->d_inode,dentry,mode,&nd);
    break;
    @@ -1928,14 +1941,11 @@ asmlinkage long sys_mknodat(int dfd, con
    case S_IFIFO: case S_IFSOCK:
    error = vfs_mknod(nd.dentry->d_inode,dentry,mode,0);
    break;
    - case S_IFDIR:
    - error = -EPERM;
    - break;
    - default:
    - error = -EINVAL;
    - }
    - dput(dentry);
    }
    + mnt_drop_write(nd.mnt);
    +out_dput:
    + dput(dentry);
    +out_unlock:
    mutex_unlock(&nd.dentry->d_inode->i_mutex);
    path_release(&nd);
    out:
    diff -puN fs/nfsd/vfs.c~sys-mknodat-elevate-write-count-for-vfs-mknod-create fs/nfsd/vfs.c
    --- lxc/fs/nfsd/vfs.c~sys-mknodat-elevate-write-count-for-vfs-mknod-create 2007-07-10 12:46:15.000000000 -0700
    +++ lxc-dave/fs/nfsd/vfs.c 2007-07-10 12:46:15.000000000 -0700
    @@ -1199,7 +1199,11 @@ nfsd_create(struct svc_rqst *rqstp, stru
    case S_IFBLK:
    case S_IFIFO:
    case S_IFSOCK:
    + host_err = mnt_want_write(fhp->fh_export->ex_mnt);
    + if (host_err)
    + break;
    host_err = vfs_mknod(dirp, dchild, iap->ia_mode, rdev);
    + mnt_drop_write(fhp->fh_export->ex_mnt);
    break;
    default:
    printk("nfsd: bad file type %o in nfsd_create\n", type);
    diff -puN net/unix/af_unix.c~sys-mknodat-elevate-write-count-for-vfs-mknod-create net/unix/af_unix.c
    --- lxc/net/unix/af_unix.c~sys-mknodat-elevate-write-count-for-vfs-mknod-create 2007-07-10 12:46:15.000000000 -0700
    +++ lxc-dave/net/unix/af_unix.c 2007-07-10 12:46:15.000000000 -0700
    @@ -815,7 +815,11 @@ static int unix_bind(struct socket *sock
    */
    mode = S_IFSOCK |
    (SOCK_INODE(sock)->i_mode & ~current->fs->umask);
    + err = mnt_want_write(nd.mnt);
    + if (err)
    + goto out_mknod_dput;
    err = vfs_mknod(nd.dentry->d_inode, dentry, mode, 0);
    + mnt_drop_write(nd.mnt);
    if (err)
    goto out_mknod_dput;
    mutex_unlock(&nd.dentry->d_inode->i_mutex);
    _
    -
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