4.9-stable review patch.  If anyone has any objections, please let me know.


From: Dmitry Vyukov <dvyu...@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-dvyu...@google.com
Fixes: 5c9a8750a640 ("kernel: add kcov code coverage")
Signed-off-by: Dmitry Vyukov <dvyu...@google.com>
Reported-by: Shankara Pailoor <sp3...@columbia.edu>
Cc: Dmitry Vyukov <dvyu...@google.com>
Cc: syzbot <syzkal...@googlegroups.com>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

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

--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -220,9 +220,9 @@ 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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