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Subject[PATCH] kcov: detect double association with a single task
Date
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@google.com>
Reported-by: Shankara Pailoor <sp3485@columbia.edu>
Fixes: 5c9a8750a640 ("kernel: add kcov code coverage")
Cc: syzkaller@googlegroups.com
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.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
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