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    Subject[PATCH 08/14] Implement fsmount() to effect a pre-configured mount [ver #2]
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    Provide a system call by which a filesystem opened with fsopen() and
    configured by a series of writes can be mounted:

    int ret = fsmount(int fsfd, int dfd, const char *path,
    unsigned int at_flags, unsigned int flags);

    where fsfd is the fd returned by fsopen(), dfd, path and at_flags locate
    the mountpoint and flags are the applicable MS_* flags. dfd can be
    AT_FDCWD or an fd open to a directory.

    In the event that fsmount() fails, it may be possible to get an error
    message by calling read(). If no message is available, ENODATA will be
    reported.

    Signed-off-by: David Howells <dhowells@redhat.com>
    ---

    arch/x86/entry/syscalls/syscall_32.tbl | 1
    arch/x86/entry/syscalls/syscall_64.tbl | 1
    fs/namespace.c | 99 ++++++++++++++++++++++++++++++++
    include/linux/lsm_hooks.h | 6 ++
    include/linux/security.h | 6 ++
    include/linux/syscalls.h | 2 +
    kernel/sys_ni.c | 1
    security/security.c | 7 ++
    security/selinux/hooks.c | 13 ++++
    9 files changed, 136 insertions(+)

    diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
    index 9bf8d4c62f85..abe6ea95e0e6 100644
    --- a/arch/x86/entry/syscalls/syscall_32.tbl
    +++ b/arch/x86/entry/syscalls/syscall_32.tbl
    @@ -392,3 +392,4 @@
    383 i386 statx sys_statx
    384 i386 arch_prctl sys_arch_prctl compat_sys_arch_prctl
    385 i386 fsopen sys_fsopen
    +386 i386 fsmount sys_fsmount
    diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
    index 9b198c5fc412..0977c5079831 100644
    --- a/arch/x86/entry/syscalls/syscall_64.tbl
    +++ b/arch/x86/entry/syscalls/syscall_64.tbl
    @@ -340,6 +340,7 @@
    331 common pkey_free sys_pkey_free
    332 common statx sys_statx
    333 common fsopen sys_fsopen
    +334 common fsmount sys_fsmount

    #
    # x32-specific system call numbers start at 512 to avoid cache impact
    diff --git a/fs/namespace.c b/fs/namespace.c
    index 8ade7252ee34..6e43657d78bd 100644
    --- a/fs/namespace.c
    +++ b/fs/namespace.c
    @@ -3253,6 +3253,105 @@ vfs_submount_sc(const struct dentry *mountpoint, struct sb_config *sc)
    EXPORT_SYMBOL_GPL(vfs_submount_sc);

    /*
    + * Mount a new, prepared superblock (specified by fs_fd) on the location
    + * specified by dfd and dir_name. dfd can be AT_FDCWD, a dir fd or a container
    + * fd. This cannot be used for binding, moving or remounting mounts.
    + */
    +SYSCALL_DEFINE5(fsmount, int, fs_fd, int, dfd, const char __user *, dir_name,
    + unsigned int, at_flags, unsigned int, flags)
    +{
    + struct sb_config *sc;
    + struct inode *inode;
    + struct path mountpoint;
    + struct fd f;
    + unsigned int lookup_flags, mnt_flags = 0;
    + long ret;
    +
    + if ((at_flags & ~(AT_SYMLINK_NOFOLLOW | AT_NO_AUTOMOUNT |
    + AT_EMPTY_PATH)) != 0)
    + return -EINVAL;
    +
    + if (flags & ~(MS_RDONLY | MS_NOSUID | MS_NODEV | MS_NOEXEC |
    + MS_NOATIME | MS_NODIRATIME | MS_RELATIME | MS_STRICTATIME))
    + return -EINVAL;
    +
    + if (flags & MS_RDONLY)
    + mnt_flags |= MNT_READONLY;
    + if (flags & MS_NOSUID)
    + mnt_flags |= MNT_NOSUID;
    + if (flags & MS_NODEV)
    + mnt_flags |= MNT_NODEV;
    + if (flags & MS_NOEXEC)
    + mnt_flags |= MNT_NOEXEC;
    + if (flags & MS_NODIRATIME)
    + mnt_flags |= MNT_NODIRATIME;
    +
    + if (flags & MS_STRICTATIME) {
    + if (flags & MS_NOATIME)
    + return -EINVAL;
    + } else if (flags & MS_NOATIME) {
    + mnt_flags |= MNT_NOATIME;
    + } else {
    + mnt_flags |= MNT_RELATIME;
    + }
    +
    + f = fdget(fs_fd);
    + if (!f.file)
    + return -EBADF;
    +
    + ret = -EINVAL;
    + if (f.file->f_op != &fs_fs_fops)
    + goto err_fsfd;
    +
    + sc = f.file->private_data;
    +
    + ret = -EPERM;
    + if (!may_mount() ||
    + ((sc->ms_flags & MS_MANDLOCK) && !may_mandlock()))
    + goto err_fsfd;
    +
    + /* Prevent further changes. */
    + inode = file_inode(f.file);
    + ret = inode_lock_killable(inode);
    + if (ret < 0)
    + goto err_fsfd;
    + ret = -EBUSY;
    + if (!sc->mounted) {
    + sc->mounted = true;
    + ret = 0;
    + }
    + inode_unlock(inode);
    + if (ret < 0)
    + goto err_fsfd;
    +
    + /* Find the mountpoint. A container can be specified in dfd. */
    + lookup_flags = LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT;
    + if (at_flags & AT_SYMLINK_NOFOLLOW)
    + lookup_flags &= ~LOOKUP_FOLLOW;
    + if (at_flags & AT_NO_AUTOMOUNT)
    + lookup_flags &= ~LOOKUP_AUTOMOUNT;
    + if (at_flags & AT_EMPTY_PATH)
    + lookup_flags |= LOOKUP_EMPTY;
    + ret = user_path_at(dfd, dir_name, lookup_flags, &mountpoint);
    + if (ret < 0) {
    + sb_cfg_error(sc, "VFS: Mountpoint lookup failed");
    + goto err_fsfd;
    + }
    +
    + ret = security_sb_config_mountpoint(sc, &mountpoint);
    + if (ret < 0)
    + goto err_mp;
    +
    + ret = do_new_mount_sc(sc, &mountpoint, mnt_flags);
    +
    +err_mp:
    + path_put(&mountpoint);
    +err_fsfd:
    + fdput(f);
    + return ret;
    +}
    +
    +/*
    * Return true if path is reachable from root
    *
    * namespace_sem or mount_lock is held
    diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
    index 6238fccaf5a4..e8e473ce5ddd 100644
    --- a/include/linux/lsm_hooks.h
    +++ b/include/linux/lsm_hooks.h
    @@ -101,6 +101,10 @@
    * Equivalent of sb_kern_mount, but with a superblock configuration context.
    * @sc indicates the superblock configuration context.
    * @src_sb indicates the new superblock.
    + * @sb_config_mountpoint:
    + * Equivalent of sb_mount, but with an sb_config.
    + * @sc indicates the superblock configuration context.
    + * @mountpoint indicates the path on which the mount will take place.
    *
    * Security hooks for filesystem operations.
    *
    @@ -1390,6 +1394,7 @@ union security_list_options {
    void (*sb_config_free)(struct sb_config *sc);
    int (*sb_config_parse_option)(struct sb_config *sc, char *opt);
    int (*sb_config_kern_mount)(struct sb_config *sc, struct super_block *sb);
    + int (*sb_config_mountpoint)(struct sb_config *sc, struct path *mountpoint);

    int (*sb_alloc_security)(struct super_block *sb);
    void (*sb_free_security)(struct super_block *sb);
    @@ -1704,6 +1709,7 @@ struct security_hook_heads {
    struct list_head sb_config_free;
    struct list_head sb_config_parse_option;
    struct list_head sb_config_kern_mount;
    + struct list_head sb_config_mountpoint;
    struct list_head sb_alloc_security;
    struct list_head sb_free_security;
    struct list_head sb_copy_data;
    diff --git a/include/linux/security.h b/include/linux/security.h
    index 49a7254aa30a..f95dc555cf29 100644
    --- a/include/linux/security.h
    +++ b/include/linux/security.h
    @@ -226,6 +226,7 @@ int security_sb_config_dup(struct sb_config *sc, struct sb_config *src_sc);
    void security_sb_config_free(struct sb_config *sc);
    int security_sb_config_parse_option(struct sb_config *sc, char *opt);
    int security_sb_config_kern_mount(struct sb_config *sc, struct super_block *sb);
    +int security_sb_config_mountpoint(struct sb_config *sc, struct path *mountpoint);
    int security_sb_alloc(struct super_block *sb);
    void security_sb_free(struct super_block *sb);
    int security_sb_copy_data(char *orig, char *copy);
    @@ -541,6 +542,11 @@ static inline int security_sb_config_kern_mount(struct sb_config *sc,
    {
    return 0;
    }
    +static inline int security_sb_config_mountpoint(struct sb_config *sc,
    + struct path *mountpoint)
    +{
    + return 0;
    +}

    static inline int security_sb_alloc(struct super_block *sb)
    {
    diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
    index 91ec8802ad5d..07e4f775f24d 100644
    --- a/include/linux/syscalls.h
    +++ b/include/linux/syscalls.h
    @@ -906,5 +906,7 @@ asmlinkage long sys_pkey_free(int pkey);
    asmlinkage long sys_statx(int dfd, const char __user *path, unsigned flags,
    unsigned mask, struct statx __user *buffer);
    asmlinkage long sys_fsopen(const char *fs_name, int containerfd, unsigned int flags);
    +asmlinkage long sys_fsmount(int fsfd, int dfd, const char *path, unsigned int at_flags,
    + unsigned int flags);

    #endif
    diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
    index de1dc63e7e47..a0fe764bd5dd 100644
    --- a/kernel/sys_ni.c
    +++ b/kernel/sys_ni.c
    @@ -261,3 +261,4 @@ cond_syscall(sys_pkey_free);

    /* fd-based mount */
    cond_syscall(sys_fsopen);
    +cond_syscall(sys_fsmount);
    diff --git a/security/security.c b/security/security.c
    index fa9037186634..8b2b7e6b3112 100644
    --- a/security/security.c
    +++ b/security/security.c
    @@ -334,6 +334,11 @@ int security_sb_config_kern_mount(struct sb_config *sc, struct super_block *sb)
    return call_int_hook(sb_config_kern_mount, 0, sc, sb);
    }

    +int security_sb_config_mountpoint(struct sb_config *sc, struct path *mountpoint)
    +{
    + return call_int_hook(sb_config_mountpoint, 0, sc, mountpoint);
    +}
    +
    int security_sb_alloc(struct super_block *sb)
    {
    return call_int_hook(sb_alloc_security, 0, sb);
    @@ -1691,6 +1696,8 @@ struct security_hook_heads security_hook_heads = {
    LIST_HEAD_INIT(security_hook_heads.sb_config_parse_option),
    .sb_config_kern_mount =
    LIST_HEAD_INIT(security_hook_heads.sb_config_kern_mount),
    + .sb_config_mountpoint =
    + LIST_HEAD_INIT(security_hook_heads.sb_config_mountpoint),
    .sb_alloc_security =
    LIST_HEAD_INIT(security_hook_heads.sb_alloc_security),
    .sb_free_security =
    diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
    index 142be91888c9..e1bf18af72f5 100644
    --- a/security/selinux/hooks.c
    +++ b/security/selinux/hooks.c
    @@ -2990,6 +2990,18 @@ static int selinux_sb_config_kern_mount(struct sb_config *sc,
    return rc;
    }

    +static int selinux_sb_config_mountpoint(struct sb_config *sc,
    + struct path *mountpoint)
    +{
    + const struct cred *cred = current_cred();
    + int ret;
    +
    + ret = path_has_perm(cred, mountpoint, FILE__MOUNTON);
    + if (ret < 0)
    + sb_cfg_error(sc, "SELinux: Mount on mountpoint not permitted");
    + return ret;
    +}
    +
    /* inode security operations */

    static int selinux_inode_alloc_security(struct inode *inode)
    @@ -6300,6 +6312,7 @@ static struct security_hook_list selinux_hooks[] = {
    LSM_HOOK_INIT(sb_config_free, selinux_sb_config_free),
    LSM_HOOK_INIT(sb_config_parse_option, selinux_sb_config_parse_option),
    LSM_HOOK_INIT(sb_config_kern_mount, selinux_sb_config_kern_mount),
    + LSM_HOOK_INIT(sb_config_mountpoint, selinux_sb_config_mountpoint),

    LSM_HOOK_INIT(sb_alloc_security, selinux_sb_alloc_security),
    LSM_HOOK_INIT(sb_free_security, selinux_sb_free_security),
    \
     
     \ /
      Last update: 2017-05-11 18:32    [W:2.188 / U:0.132 seconds]
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