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    Subject[PATCH 6/6] Add an AT_NO_AUTOMOUNT flag to suppress terminal automount [ver #2]
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    From

    This is an update required because the first patch in the series was also
    altered in the same area.

    David
    ---
    From: David Howells <dhowells@redhat.com>
    Subject: [PATCH] Add an AT_NO_AUTOMOUNT flag to suppress terminal automount

    Add an AT_NO_AUTOMOUNT flag to suppress terminal automounting of directories
    with follow_link semantics. This can be used by fstatat() 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 | 6 ++++++
    fs/stat.c | 4 +++-
    include/linux/fcntl.h | 1 +
    include/linux/namei.h | 2 ++
    4 files changed, 12 insertions(+), 1 deletions(-)


    diff --git a/fs/namei.c b/fs/namei.c
    index f2910b7..c154112 100644
    --- a/fs/namei.c
    +++ b/fs/namei.c
    @@ -629,6 +629,12 @@ static int follow_automount(struct path *path, unsigned flags, int res)
    if (!path->dentry->d_op || !path->dentry->d_op->d_automount)
    return -EREMOTE;

    + /* We don't want to mount if someone supplied AT_NO_AUTOMOUNT
    + * and this is the terminal part of the path.
    + */
    + if ((flags & LOOKUP_NO_AUTOMOUNT) && !(flags & LOOKUP_CONTINUE))
    + return -EXDEV; /* we actually want to stop here */
    +
    /* We want to mount if someone is trying to open/create a file of any
    * type under the mountpoint, wants to traverse through the mountpoint
    * or wants to open the mounted directory.
    diff --git a/fs/stat.c b/fs/stat.c
    index c4ecd52..bae6fa2 100644
    --- a/fs/stat.c
    +++ b/fs/stat.c
    @@ -74,11 +74,13 @@ int vfs_fstatat(int dfd, char __user *filename, struct kstat *stat, int flag)
    int error = -EINVAL;
    int lookup_flags = 0;

    - if ((flag & ~AT_SYMLINK_NOFOLLOW) != 0)
    + if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_NO_AUTOMOUNT)) != 0)
    goto out;

    if (!(flag & AT_SYMLINK_NOFOLLOW))
    lookup_flags |= LOOKUP_FOLLOW;
    + if (flag & AT_NO_AUTOMOUNT)
    + lookup_flags |= LOOKUP_NO_AUTOMOUNT;

    error = user_path_at(dfd, filename, lookup_flags, &path);
    if (error)
    diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h
    index afc00af..a562fa5 100644
    --- a/include/linux/fcntl.h
    +++ b/include/linux/fcntl.h
    @@ -45,6 +45,7 @@
    #define AT_REMOVEDIR 0x200 /* Remove directory instead of
    unlinking file. */
    #define AT_SYMLINK_FOLLOW 0x400 /* Follow symbolic links. */
    +#define AT_NO_AUTOMOUNT 0x800 /* 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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