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    Subject[PATCH 4.14 034/159] kcov: detect double association with a single task
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

    From: Dmitry Vyukov <dvyukov@google.com>

    commit a77660d231f8b3d84fd23ed482e0964f7aa546d6 upstream.

    Currently KCOV_ENABLE does not check if the current task is already
    associated with another kcov descriptor. As the result it is possible
    to associate a single task with more than one kcov descriptor, which
    later leads to a memory leak of the old descriptor. This relation is
    really meant to be one-to-one (task has only one back link).

    Extend validation to detect such misuse.

    Link: http://lkml.kernel.org/r/20180122082520.15716-1-dvyukov@google.com
    Fixes: 5c9a8750a640 ("kernel: add kcov code coverage")
    Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
    Reported-by: Shankara Pailoor <sp3485@columbia.edu>
    Cc: Dmitry Vyukov <dvyukov@google.com>
    Cc: syzbot <syzkaller@googlegroups.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/kcov.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/kernel/kcov.c
    +++ b/kernel/kcov.c
    @@ -225,9 +225,9 @@ static int kcov_ioctl_locked(struct kcov
    if (unused != 0 || kcov->mode == KCOV_MODE_DISABLED ||
    kcov->area == NULL)
    return -EINVAL;
    - if (kcov->t != NULL)
    - return -EBUSY;
    t = current;
    + if (kcov->t != NULL || t->kcov != NULL)
    + return -EBUSY;
    /* Cache in task struct for performance. */
    t->kcov_size = kcov->size;
    t->kcov_area = kcov->area;

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