linux-kernel - [PATCH] kcov: detect double association with a single task

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Message-Id: <20180122082520.15716-1-dvyukov@google.com>
Date:   Mon, 22 Jan 2018 09:25:20 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     akpm@...ux-foundation.org
Cc:     sp3485@...umbia.edu, andrew.aday@...umbia.edu,
        Dmitry Vyukov <dvyukov@...gle.com>, syzkaller@...glegroups.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH] kcov: detect double association with a single task

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.

Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
Reported-by: Shankara Pailoor <sp3485@...umbia.edu>
Fixes: 5c9a8750a640 ("kernel: add kcov code coverage")
Cc: syzkaller@...glegroups.com
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
---
 kernel/kcov.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 7594c033d98a..2c16f1ab5e10 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -358,7 +358,8 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
 		 */
 		if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
 			return -EINVAL;
-		if (kcov->t != NULL)
+		t = current;
+		if (kcov->t != NULL || t->kcov != NULL)
 			return -EBUSY;
 		if (arg == KCOV_TRACE_PC)
 			kcov->mode = KCOV_MODE_TRACE_PC;
@@ -370,7 +371,6 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
 #endif
 		else
 			return -EINVAL;
-		t = current;
 		/* Cache in task struct for performance. */
 		t->kcov_size = kcov->size;
 		t->kcov_area = kcov->area;
-- 
2.16.0.rc1.238.g530d649a79-goog