[PATCH 4.14 034/159] kcov: detect double association with a single task

[Greg Kroah-Hartman]

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

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

From: Dmitry Vyukov <dvyukov@xxxxxxxxxx>

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@xxxxxxxxxx
Fixes: 5c9a8750a640 ("kernel: add kcov code coverage")
Signed-off-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Reported-by: Shankara Pailoor <sp3485@xxxxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 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;