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    Subject[patch 133/164] vfs: add NOFOLLOW flag to umount(2)
    2.6.33-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Miklos Szeredi <mszeredi@suse.cz>

    commit db1f05bb85d7966b9176e293f3ceead1cb8b5d79 upstream.

    Add a new UMOUNT_NOFOLLOW flag to umount(2). This is needed to prevent
    symlink attacks in unprivileged unmounts (fuse, samba, ncpfs).

    Additionally, return -EINVAL if an unknown flag is used (and specify
    an explicitly unused flag: UMOUNT_UNUSED). This makes it possible for
    the caller to determine if a flag is supported or not.

    CC: Eugene Teo <eugene@redhat.com>
    CC: Michael Kerrisk <mtk.manpages@gmail.com>
    Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    fs/namespace.c | 9 ++++++++-
    include/linux/fs.h | 2 ++
    2 files changed, 10 insertions(+), 1 deletion(-)

    --- a/fs/namespace.c
    +++ b/fs/namespace.c
    @@ -1121,8 +1121,15 @@ SYSCALL_DEFINE2(umount, char __user *, n
    {
    struct path path;
    int retval;
    + int lookup_flags = 0;

    - retval = user_path(name, &path);
    + if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
    + return -EINVAL;
    +
    + if (!(flags & UMOUNT_NOFOLLOW))
    + lookup_flags |= LOOKUP_FOLLOW;
    +
    + retval = user_path_at(AT_FDCWD, name, lookup_flags, &path);
    if (retval)
    goto out;
    retval = -EINVAL;
    --- a/include/linux/fs.h
    +++ b/include/linux/fs.h
    @@ -1308,6 +1308,8 @@ extern int send_sigurg(struct fown_struc
    #define MNT_FORCE 0x00000001 /* Attempt to forcibily umount */
    #define MNT_DETACH 0x00000002 /* Just detach from the tree */
    #define MNT_EXPIRE 0x00000004 /* Mark for expiry */
    +#define UMOUNT_NOFOLLOW 0x00000008 /* Don't follow symlink on umount */
    +#define UMOUNT_UNUSED 0x80000000 /* Flag guaranteed to be unused */

    extern struct list_head super_blocks;
    extern spinlock_t sb_lock;



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