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    Subject[PATCH 4.4 108/118] asm-generic: make copy_from_user() zero the destination properly
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

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

    From: Al Viro <viro@zeniv.linux.org.uk>

    commit 2545e5da080b4839dd859e3b09343a884f6ab0e3 upstream.

    ... in all cases, including the failing access_ok()

    Note that some architectures using asm-generic/uaccess.h have
    __copy_from_user() not zeroing the tail on failure halfway
    through. This variant works either way.

    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    include/asm-generic/uaccess.h | 10 ++++++----
    1 file changed, 6 insertions(+), 4 deletions(-)

    --- a/include/asm-generic/uaccess.h
    +++ b/include/asm-generic/uaccess.h
    @@ -261,11 +261,13 @@ extern int __get_user_bad(void) __attrib
    static inline long copy_from_user(void *to,
    const void __user * from, unsigned long n)
    {
    + unsigned long res = n;
    might_fault();
    - if (access_ok(VERIFY_READ, from, n))
    - return __copy_from_user(to, from, n);
    - else
    - return n;
    + if (likely(access_ok(VERIFY_READ, from, n)))
    + res = __copy_from_user(to, from, n);
    + if (unlikely(res))
    + memset(to + (n - res), 0, res);
    + return res;
    }

    static inline long copy_to_user(void __user *to,

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