lkml.org 
[lkml]   [2007]   [Apr]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[patch 07/10] unprivileged mounts: allow unprivileged mounts
    From: Miklos Szeredi <mszeredi@suse.cz>

    Define a new fs flag FS_SAFE, which denotes, that unprivileged mounting of
    this filesystem may not constitute a security problem.

    Since most filesystems haven't been designed with unprivileged mounting in
    mind, a thorough audit is needed before setting this flag.

    For "safe" filesystems also allow unprivileged forced unmounting.

    Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
    ---

    Index: linux/fs/namespace.c
    ===================================================================
    --- linux.orig/fs/namespace.c 2007-04-26 13:30:04.000000000 +0200
    +++ linux/fs/namespace.c 2007-04-26 13:51:29.000000000 +0200
    @@ -724,14 +724,16 @@ static bool is_mount_owner(struct vfsmou
    /*
    * umount is permitted for
    * - sysadmin
    - * - mount owner, if not forced umount
    + * - mount owner
    + * o if not forced umount,
    + * o if forced umount, and filesystem is "safe"
    */
    static bool permit_umount(struct vfsmount *mnt, int flags)
    {
    if (capable(CAP_SYS_ADMIN))
    return true;

    - if (flags & MNT_FORCE)
    + if ((flags & MNT_FORCE) && !(mnt->mnt_sb->s_type->fs_flags & FS_SAFE))
    return false;

    return is_mount_owner(mnt, current->fsuid);
    @@ -787,13 +789,17 @@ asmlinkage long sys_oldumount(char __use
    * - mountpoint is not a symlink
    * - mountpoint is in a mount owned by the user
    */
    -static bool permit_mount(struct nameidata *nd, int *flags)
    +static bool permit_mount(struct nameidata *nd, struct file_system_type *type,
    + int *flags)
    {
    struct inode *inode = nd->dentry->d_inode;

    if (capable(CAP_SYS_ADMIN))
    return true;

    + if (type && !(type->fs_flags & FS_SAFE))
    + return false;
    +
    if (S_ISLNK(inode->i_mode))
    return false;

    @@ -1027,7 +1033,7 @@ static int do_loopback(struct nameidata
    struct vfsmount *mnt = NULL;
    int err;

    - if (!permit_mount(nd, &flags))
    + if (!permit_mount(nd, NULL, &flags))
    return -EPERM;
    if (!old_name || !*old_name)
    return -EINVAL;
    @@ -1188,26 +1194,46 @@ out:
    * create a new mount for userspace and request it to be added into the
    * namespace's tree
    */
    -static int do_new_mount(struct nameidata *nd, char *type, int flags,
    +static int do_new_mount(struct nameidata *nd, char *fstype, int flags,
    int mnt_flags, char *name, void *data)
    {
    + int err;
    struct vfsmount *mnt;
    + struct file_system_type *type;

    - if (!type || !memchr(type, 0, PAGE_SIZE))
    + if (!fstype || !memchr(fstype, 0, PAGE_SIZE))
    return -EINVAL;

    - /* we need capabilities... */
    - if (!capable(CAP_SYS_ADMIN))
    - return -EPERM;
    -
    - mnt = do_kern_mount(type, flags & ~MS_SETUSER, name, data);
    - if (IS_ERR(mnt))
    + type = get_fs_type(fstype);
    + if (!type)
    + return -ENODEV;
    +
    + err = -EPERM;
    + if (!permit_mount(nd, type, &flags))
    + goto out_put_filesystem;
    +
    + if (flags & MS_SETUSER) {
    + err = reserve_user_mount();
    + if (err)
    + goto out_put_filesystem;
    + }
    +
    + mnt = vfs_kern_mount(type, flags & ~MS_SETUSER, name, data);
    + put_filesystem(type);
    + if (IS_ERR(mnt)) {
    + if (flags & MS_SETUSER)
    + dec_nr_user_mounts();
    return PTR_ERR(mnt);
    + }

    if (flags & MS_SETUSER)
    - set_mnt_user(mnt);
    + __set_mnt_user(mnt);

    return do_add_mount(mnt, nd, mnt_flags, NULL);
    +
    + out_put_filesystem:
    + put_filesystem(type);
    + return err;
    }

    /*
    @@ -1237,7 +1263,7 @@ int do_add_mount(struct vfsmount *newmnt
    if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
    goto unlock;

    - /* MNT_USER was set earlier */
    + /* some flags may have been set earlier */
    newmnt->mnt_flags |= mnt_flags;
    if ((err = graft_tree(newmnt, nd)))
    goto unlock;
    Index: linux/include/linux/fs.h
    ===================================================================
    --- linux.orig/include/linux/fs.h 2007-04-26 13:46:26.000000000 +0200
    +++ linux/include/linux/fs.h 2007-04-26 13:48:14.000000000 +0200
    @@ -96,6 +96,7 @@ extern int dir_notify_enable;
    #define FS_REQUIRES_DEV 1
    #define FS_BINARY_MOUNTDATA 2
    #define FS_HAS_SUBTYPE 4
    +#define FS_SAFE 8 /* Safe to mount by unprivileged users */
    #define FS_REVAL_DOT 16384 /* Check the paths ".", ".." for staleness */
    #define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move()
    * during rename() internally.
    --
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-04-27 14:11    [W:0.032 / U:62.320 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site