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    Subject[PATCH 17/18] xstat: Add an AT_NO_AUTOMOUNT flag to suppress terminal automount [ver #6]
    Date
    Add an AT_NO_AUTOMOUNT flag to suppress terminal automounting of directories
    with follow_link semantics. This can be used by fstatat()/xstat() users to
    permit the gathering of attributes on an automount point and also prevent
    mass-automounting of a directory of automount points by ls.

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

    fs/namei.c | 15 ++++++++++-----
    fs/stat.c | 4 +++-
    include/linux/fcntl.h | 1 +
    include/linux/namei.h | 2 ++
    4 files changed, 16 insertions(+), 6 deletions(-)

    diff --git a/fs/namei.c b/fs/namei.c
    index 86068a2..056427e 100644
    --- a/fs/namei.c
    +++ b/fs/namei.c
    @@ -654,7 +654,8 @@ static int follow_automount(struct path *path, int res)
    /* no need for dcache_lock, as serialization is taken care in
    * namespace.c
    */
    -static int __follow_mount(struct path *path, unsigned nofollow)
    +static int __follow_mount(struct path *path, unsigned nofollow,
    + struct nameidata *nd)
    {
    struct vfsmount *mounted;
    int ret, res = 0;
    @@ -674,8 +675,12 @@ static int __follow_mount(struct path *path, unsigned nofollow)
    }
    if (!d_automount_point(path->dentry))
    break;
    - if (nofollow)
    - return -ELOOP;
    + if (!(nd->flags & LOOKUP_CONTINUE)) {
    + if (nofollow)
    + return -ELOOP;
    + if (nd->flags & LOOKUP_NO_AUTOMOUNT)
    + break;
    + }
    ret = follow_automount(path, res);
    if (ret < 0)
    return ret;
    @@ -769,7 +774,7 @@ static int do_lookup(struct nameidata *nd, struct qstr *name,
    done:
    path->mnt = mnt;
    path->dentry = dentry;
    - ret = __follow_mount(path, 0);
    + ret = __follow_mount(path, 0, nd);
    if (unlikely(ret < 0))
    path_put(path);
    return ret;
    @@ -1762,7 +1767,7 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
    if (open_flag & O_EXCL)
    goto exit_dput;

    - error = __follow_mount(path, open_flag & O_NOFOLLOW);
    + error = __follow_mount(path, open_flag & O_NOFOLLOW, nd);
    if (error < 0)
    goto exit_dput;

    diff --git a/fs/stat.c b/fs/stat.c
    index bb0f538..3f2ab5f 100644
    --- a/fs/stat.c
    +++ b/fs/stat.c
    @@ -182,11 +182,13 @@ int vfs_xstat(int dfd, const char __user *filename, int flags,
    struct path path;
    int error, lookup_flags;

    - if (flags & ~(AT_SYMLINK_NOFOLLOW | KSTAT_QUERY_FLAGS))
    + if (flags & ~(AT_SYMLINK_NOFOLLOW | AT_NO_AUTOMOUNT |
    + KSTAT_QUERY_FLAGS))
    return -EINVAL;

    stat->query_flags = flags & KSTAT_QUERY_FLAGS;
    lookup_flags = (flags & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
    + lookup_flags |= (flags & AT_NO_AUTOMOUNT) ? LOOKUP_NO_AUTOMOUNT : 0;

    error = user_path_at(dfd, filename, lookup_flags, &path);
    if (!error) {
    diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h
    index bcf8083..768b0fd 100644
    --- a/include/linux/fcntl.h
    +++ b/include/linux/fcntl.h
    @@ -46,6 +46,7 @@
    unlinking file. */
    #define AT_SYMLINK_FOLLOW 0x400 /* Follow symbolic links. */
    #define AT_FORCE_ATTR_SYNC 0x800 /* Force the attributes to be sync'd with the server */
    +#define AT_NO_AUTOMOUNT 0x1000 /* Suppress terminal automount traversal */

    #ifdef __KERNEL__

    diff --git a/include/linux/namei.h b/include/linux/namei.h
    index 05b441d..1e1febf 100644
    --- a/include/linux/namei.h
    +++ b/include/linux/namei.h
    @@ -43,12 +43,14 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND};
    * - internal "there are more path components" flag
    * - locked when lookup done with dcache_lock held
    * - dentry cache is untrusted; force a real lookup
    + * - suppress terminal automount
    */
    #define LOOKUP_FOLLOW 1
    #define LOOKUP_DIRECTORY 2
    #define LOOKUP_CONTINUE 4
    #define LOOKUP_PARENT 16
    #define LOOKUP_REVAL 64
    +#define LOOKUP_NO_AUTOMOUNT 128
    /*
    * Intent data
    */


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