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    SubjectRe: [PATCH -mm 7/8] user_ns: handle file sigio
    Serge E. Hallyn wrote:
    > Quoting Andrew Morton (
    >> On Thu, 4 Jan 2007 12:12:57 -0600
    >> "Serge E. Hallyn" <> wrote:
    >>> A process in one user namespace could set a fowner and sigio on a file in a
    >>> shared vfsmount, ending up killing a task in another user namespace.
    >>> Prevent this by adding a user namespace pointer to the fown_struct, and
    >>> enforcing that a process causing a signal to be sent be in the same
    >>> user namespace as the file owner.
    >> This patch breaks the X server (stock FC5 install) with CONFIG_USER_NS=n.
    >> Neither the USB mouse nor the trackpad work. They work OK under GPM.
    >> Setting CONFIG_USER_NS=y "fixes" this. This bug was not observed in
    >> 2.6.20-rc3-mm1 because that kernel had user-ns-always-on.patch for other
    >> reasons. (I'll restore that patch).
    >> There's nothing very interesting here:
    [ ... ]
    > I can't see any reason for this in the code or comparative ltp runs.
    > Cedric is testing on a fc6 laptop, hopefully he can reproduce it.

    I did reproduce it on a FC5 desktop finally.

    get_user_ns() returns NULL when CONFIG_USER_NS=n and this breaks
    sigio_perm() which does not expect NULL values for ->user_ns.

    I would fix this with the following patch.


    Signed-off-by: Cedric Le Goater <>

    include/linux/user_namespace.h | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    Index: 2.6.20-rc4-mm1/include/linux/user_namespace.h
    --- 2.6.20-rc4-mm1.orig/include/linux/user_namespace.h
    +++ 2.6.20-rc4-mm1/include/linux/user_namespace.h
    @@ -49,7 +49,7 @@

    static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
    - return NULL;
    + return &init_user_ns;

    static inline int unshare_user_ns(unsigned long flags,
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      Last update: 2007-01-15 16:53    [W:0.021 / U:7.864 seconds]
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